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AB - PLATFORM 1: Neurodegenerative Disease 1 1 Combining Postmortem Single Cell Analysis With An Induced Pluripotent Stem Cell Model to Study Dysregulated Pathways In FTD Osama Al Dalahmah1, Tristan Winters1, Aayushi Mahajan1, Nelson Humala1, Trang Nguyen1, Rebekka Kühn1, Michael DeTure2, Dennis Dickson2, Jean Paul Vonsattel1, Markus Siegelin1, Vilas Menon1, James Goldman1, Peter Canoll1, Gunnar Hargus1 1Columbia University Medical Center; 2Mayo Clinic, Jacksonville, Florida Frontotemporal dementia (FTD) is a heterogeneous group of early-onset dementias leading to an impairment of behavior, language and cognition. FTD can be caused by mutations in the MAPT gene encoding the microtubule-associated protein tau resulting in pronounced atrophy of the frontal and temporal lobes, basal ganglia and brain stem areas. Here, we performed single nucleus RNA sequencing (snRNA-seq) on postmortem brain tissue from FTD patients carrying the MAPTN279K mutation and from healthy control individuals to identify dysregulated pathways in patient neural cells at single cell resolution. Amongst others, we found significant changes in pathways related to cell metabolism and neuroinflammation in patient neurons that we tested further in a stem cell model of FTD using patient-derived and control individual-derived induced pluripotent stem cells (iPSCs). Patient iPSC-derived neurons with the MAPTN279K mutation demonstrated tau pathology, an impairment of neurite outgrowth and an increased but reversible oxidative stress response to inhibition of mitochondrial respiration. FTD neurons also showed altered metabolic profiles with an increased basal mitochondrial respiration, increased ATP production and an increased maximal respiratory capacity as measured by neuronal oxygen consumption indicating an increased energy demand in these cells. Interestingly, iPSC-derived FTD neurons also had a significant effect on the survival of host neurons and on glial cell responses when transplanted into the brains of immunocompromised mice indicating a potential immunomodulatory role of patient neurons in vivo. These findings demonstrate that a combinatorial approach applying snRNA-seq on patient brain tissue and a dynamic iPSC cell model comprises a powerful tool to identify disease phenotypes in neural cells at risk in FTD. Such stem cell model of FTD could also be used as a cellular platform for high-throughput drug screening assays to identify potential therapeutic targets in FTD. 2 Glial Responses to Passive Anti-tau Immunotherapy in FTLD-tau: A Human Post-Mortem Study Boram Kim1, Bailey Mikytuck1, Eunran Suh1, Garrett Gibbons1, Vivianna Van Deerlin1, Sanjeev Vaishnavi1, Meredith Spindler1, Lauren Massimo1, Murray Grossman1, John Trojanowski1, David Irwin1, Edward Lee1 1Perelman School of Medicine at the University of Pennsylvania Tau immunotherapy is currently being tested as a potential disease-modifying treatment for tauopathies. Gosuranemab (BIIB092) is a passive immunotherapy using a humanized monoclonal antibody that directly binds to the N-terminus of tau. While Gosuranemab failed to demonstrate clinical efficacy for patients with PSP in a phase 2 trial, its neuropathologic effects have never been described. In this study, we performed immunohistochemistry on post-mortem human brains of three subjects treated with Gosuranemab. Passive anti-tau immunotherapy was not associated with appreciable clearance of FTLD-tau inclusions. However, a distinctive vesicular tau immunoreactivity which colocalized with lysosomal markers was observed within perivascular astrocytes in all cases treated with Gosuranemab. Based on the morphology and their anatomical distribution, we termed this type of tau-positive astrocyte “perivascular vesicular astrocytes” (PVAs). PVAs were absent from unimmunized cases, and were morphologically and immunophenotypically distinct from tufted astrocytes seen in PSP, granular fuzzy astrocytes (GFA) seen in aging, and astrocytic plaques seen in corticobasal degeneration (CBD). Finally, Gosuranemab-treated cases also demonstrated reactive astrocytes with an unusual bushy morphology, and abundant numbers of rod-shaped microglia. Although Gosuranemab did not appear to clear FTLD-tau aggregates, these neuropathologic findings suggest that Gosuranemab treatment may be associated with glial responses, perhaps associated with altered tau homeostasis. 3 Pathologic and Clinical Variability in LATE: Focus on Quadruple-Misfolded Proteinopathy Peter Nelson1, Erin Abner1, Shama Karanth1, Merilee Teylan2, Gregory Jicha1, Matthew Cykowski3, Yuriko Katsumata1 1University of Kentucky; 2University of Washington; 3Houston Methodist Hospital Autopsy studies indicate that ∼1/4th of octogenarians’ brains harbor limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (LATE-NC). A variety of pathologic comorbidities and clinical manifestations have been described in individuals with LATE-NC. Here, we analyzed autopsy cohort data focusing on the subset of LATE-NC cases with quadruple misfolded proteins (QMP), defined by having four comorbid proteinopathies: TDP-43, A-beta, Tau, and alpha-Synuclein. Detailed neuropathologic and longitudinal clinical data were analyzed from autopsied subjects followed at the University of Kentucky Alzheimer’s Disease Research Center (UK-ADRC; n=375 included) and separately from the multicenter-derived National Alzheimer's Coordinating Center database (NACC; n=495 included, all with TDP-43 proteinopathy). Subjects with LATE-NC lacked the clinical features of FTD in almost all cases. In the community-based UK-ADRC cohort, the QMP pattern of co-pathologies was observed in 19.2% of demented subjects, equal to the prevalence of “pure” Alzheimer’s disease (AD) pathology. Among pathology-defined groups, QMP subjects had the highest dementia frequency and the lowest final MMSE scores. Longitudinal assessments revealed that persons with eventual autopsy-confirmed QMP traversed through MCI relatively quickly (1.7 years vs 2.9 years for pure AD). In the NACC analyses, clustering algorithms indicated the existence of four subgroups of TDP-43+ cases based on clinical features and co-pathologies. There was a distinct QMP-enriched cluster of TDP-43+ subjects characterized by younger age of dementia onset, swifter disease progression, more likely to have Lewy and AD co-pathologies, and less likely to have neocortical TDP-43 proteinopathy. Clinical FTD and FTLD-TDP were rare in this group. Both cohorts (UK-ADRC, NACC) showed enrichment for the APOE-e4 genotype in QMP cases, implying that different pathologies have common upstream mechanisms. Although “pure” LATE-NC (lacking AD and Lewy pathologies) may present with a mild amnestic condition among the oldest-old, the QMP pathologic pattern is often seen in younger subjects with a relatively aggressive disease course. 4 Diverse Classes of Somatic Mutations Accumulate in Individual Neurons during Human Aging Michael Miller1, Lovelace Luquette2, Zinan Zhou3, Craig Bohrson2, Alon Galor2, Javier Ganz3, Sara Bizzotto3, Michael Lodato3, Charles Gawad4, Jay West5, Christopher Walsh3, Peter Park2 1Brigham and Women's Hospital; 2Harvard Medical School; 3Boston Children's Hospital; 4Stanford University; 5BioSkryb As humans age, cells undergo a broad array of changes, affecting metabolism, membrane function, protein synthesis, epigenetics, and other processes. While classic models assumed that the genome sequence itself is unvarying across cells and during aging, recent studies have found that certain cell populations carry somatic single nucleotide variant (SNV) mutations that accumulate with age, including neurons, with consequences in neurodegenerative disease. To examine the effect of age on the genome, we performed single cell whole genome sequencing on neurons isolated from postmortem brain across human lifespan. In this study, we applied a recently developed whole genome amplification method, primary template-directed amplification (PTA). The PTA method improved the evenness of genome amplification over existing methods, elevating experimental throughput and facilitating more sensitive and specific identification of variants in single neurons. We found that neurons show increased numbers of somatic mutations with age, including SNV and insertion and deletion (indel) classes. Mutational signature analysis indicates that these somatic mutations reflect multiple clock-like age-related processes. In particular, indel signatures reflect mutational forces previously observed in human cancers but not abundant in other aging cell populations. Furthermore, these mutations affect gene function, with indels showing a particularly pronounced impact due to disruption of trinucleotide codon reading frames. The accumulation of somatic mutations of diverse classes highlights genomic variation during neuronal aging, which compounds with other cellular insults in neurodegeneration. 5 Multigranular Topological Analysis of Single Cells Integrates the Glial Landscape of Retinal and Brain Degeneration Marcello DiStasio1, Manik Kuchroo2, Eda Calapkulu3, Maryam Ige4, Le Zhang5, Amar Sheth4, Brian Hafler6, Smita Krishnaswamy7, Scott Gigante8, Jessie Huang9, Rahul Dhodapkar4, Bastian Rieck10, Guy Wold11, Madhvi Menon12 1Department of Pathology, Yale School of Medicine; 2Department of Neuroscience, Yale School of Medicine; 3Department of Ophthalmology and Visual Science, Yale School of Medicine; 4Yale School of Medicine; 5Department of Neurology, Yale School of Medicine; 6Departments of Pathology and Ophthalmology, Yale School of Medicine; 7Departments of Computer Science and Genetics, Yale University; 8Computational Biology, Bioinformatics Program, Yale University; 9Department of Computer Science, Yale University; 10Department of Biosystems Science and Engineering, ETH Zurich; 11Department of Mathematics and Statistics, Université de Montréal; 12Division of Infection, Immunity and Respiratory Medicine, Manchester Age-related macular degeneration (AMD) is a progressive neurodegenerative disease of the retina. Though many of the changes of the retina in AMD are distinct from those seen in neurodegenerative diseases of the brain, the immune system of the retina shares many features with that of the rest of the central nervous system. We therefore hypothesized that microglia and astrocytes in the early and late stages of AMD, Alzheimer disease, and multiple sclerosis may share a transcriptional landscape that could be exploited to reveal targetable glial states. Glia are known to have multiple possible functional polarizations depending on the nature of the pathology affecting the tissue in which they reside. To allow us to make meaningful comparisons between states of glia as assessed by single nucleus RNA sequencing, we developed and applied a novel population discovery pipeline centered around a topological data analysis approach called ‘diffusion condensation’ (DC). This method sweeps through all levels of analysis granularity and, together with a single cell differential expression analysis tool called MELD, is able to identify, in an unbiased manner, comparable subpopulations in disparate diseases. We sequenced 50,498 single cells from AMD retinas in early (‘dry’) and late (neovascular or ‘wet’) stages as well as controls. In this data set we identified microglia and astrocyte populations enriched in the early phase of disease, and we validated their presence in retina using RNAscope. Applying our framework to single cell data generated from Alzheimer’s disease and multiple sclerosis, we found transcriptionally related populations enriched in the early phases of these diseases as well. We also identified an AMD-specific proangiogenic astrocyte state promoting neovascularization in advanced AMD, the likely target of anti-VEGF therapy. Finally, by mapping AMD-associated genes to glial states, we identified key signaling interactions centered around C3 and APOE, providing targets for therapeutic intervention. 6 Charactering the Heterogeneity of Adult-Onset Leukoencephalopathy with Axonal Spheroids: A Digital Spatial Profiling Study Peter Liu1, Chelsey Zhao1, Murad Alturkustani2, Lee Cyn Ang1, Qi Zhang1 1Pathology and Laboratory Medicine, Western University, Ontario, Canada; 2Pathology, King Abdulaziz University, Jeddah, Saudi Arabia Introduction: Adult-onset leukoencephalopathy with axonal spheroids (ALAS) is a group of hereditary, progressive, neurodegetative disorders involving primarily the central nervous system white matter (WM). ALAS is characterized by patchy, asymmetrical myelin loss and axonal destruction in the WM, predominantly involving the frontoparietal regions. The subcortical U-fibers are usually spared. The discovery of mutations in colony stimulating factor 1 receptor (CSF1R) gene suggests microgliopathy as a potential mechanism for this disease. However, the asymmetrical and heterogenous involvement of different brain regions remains poorly characterized. Methods: In this study, five autopsy-confirmed ALAS cases were examined. Nanostring GeoMX Digital Spatial Profiling (DSP) was performed to investigate the region-specific expressions of 60 proteins, across neural cell profiling, glial cell subtyping, immune activation status, autophagy and MAP kinase signaling. The region of interests (ROIs) were selected based on the expression of myelin basic protein (MBP) and Luxol Fast Blue (LFB) stain, representing subcortical U-fiber (ROI-1), subcortical WM immediate adjacent to U-fiber (ROI-2), WM with extensive degeneration (ROI-3), WM with no or mild degeneration (ROI-4), cerebral cortex above ROI-3 (ROI-5), and cerebral cortex above ROI-4 (ROI-6). Results: Homeostatic/resting microglia marker (TMEM119) was significantly higher in WM with no/mild degeneration (ROI-4), whereas the polarized markers (CD80, CD163, GPMBP, SPP1, and CD44) are enriched in WM with severe degeneration (ROI-3). CD9, a tetraspanin protein expressed by oligodendrocyte progenitor cells and pre-myelinating oligodendrocytes, shows increased expression in U-fiber (ROI-1). BAG3, an antiapoptotic and co-chaperone protein, is highly expressed in ROI-3. There are no significant differences identified between the cortical ROIs. Conclusions: Using a high-plex and high-throughput method, we provide evidence of regional heterogeneity in ALAS, particularly involving key markers of microglia composition, glial cell subtype and macroautophagy. 7 Quantitative TDP-43 Burden and Distribution in Old Age High and Low Probability Alzheimer’s Disease and Genetic FTLD-TDP-43 Marina Buciuc1, Jennifer Whitwell2, Matthew Baker3, Rosa Rademakers3, Dennis Dickson3, Keith Josephs1 1Department of Neurology, Mayo Clinic, Rochester, MN; 2Department of Radiology, Mayo Clinic, Rochester, MN; 3Department of Neuroscience, Mayo Clinic, Jacksonville, FL Background: TDP-43 inclusions are observed in genetic frontotemporal lobar degeneration (gFTLD-TDP), in Alzheimer’s disease (AD-TDP), and in brains of patients without other advanced co-pathologies (pure-TDP). While phenotypic presentations of these three groups of patients might differ, it is unclear whether clinical presentations and TDP-43 burden and distribution differ among these three groups in “old patients”. Methods: The brain bank at Mayo clinic, FL was queried for cases ≥75 years old at death and having TDP-43 inclusions in middle frontal cortex. Cases meeting criteria were split into the following groups: 1) gFTLD-TDP (n=15) – 7 with progranulin (GRN), 8 with C9ORF72 mutations; 2) AD-TDP (n=10) – cases with median Braak neurofibrillary tangle (NFT) stage VI, amyloid-beta Thal phase V; 3) pure-TDP (n=10) –cases with median Braak NFT I and Thal phase I. Demographic and clinical data were abstracted from medical records; TDP-43 burden was calculated using digital pathology for hippocampal subfields, entorhinal, and middle frontal cortex. Results: Amnestic Alzheimer’s dementia was the clinical diagnosis in ≥50%, regardless of group. The distribution of TDP-43 burden in gFTLD-TDP and AD-TDP, but not pure-TDP, was limbic-predominant. gFTLD-TDP showed higher TDP-43 burden in entorhinal cortex compared to those with AD-TDP (p=0.047). TDP-43 burden in middle frontal cortex did not differ between the three groups. Within gFTLD-TDP, C9ORF72 cases had higher TDP-43 burden across all regions, reaching significance in the entorhinal cortex (p=0.045), but similar limbic-predominant distribution. Conclusions: In old age, it is challenging to clinically and pathologically differentiate mutation associated FTLD-TDP from Alzheimer’s associated and pure TDP-43 cases based on TDP-43 burden or distribution. Like AD-TDP, old age mutation-associated FTLD also have a limbic-predominant TDP-43 distribution. The fact that amnestic Alzheimer’s dementia was the most common clinical diagnosis regardless of group, suggests that TDP-43 directly and indirectly targets limbic regions. 8 Comorbid Neurodegenerative Pathologies in Brains with Huntington Disease Richard Hickman1, Ramita Dewan2, Etty Cortes3, Bryan Traynor2, Jean-Paul Vonsattel1 1Columbia University Irving Medical Center; 2National Institute on Aging, USA; 3Mount Sinai School of Medicine Although Huntington disease (HD) is a monogenetic disorder driven by pathogenic CAG repeat expansion of the Huntingtin (HTT) gene, there is variation in disease severity and life expectancy. Comorbid neurodegenerative pathologies (CNP) commonly occur in older individuals with neurodegenerative disease, however, few reports document CNP in HD. HTT gene expansion has also been associated with frontotemporal lobar degeneration/ amyotrophic lateral sclerosis (FTLD/ALS) (1). We therefore reviewed 2 independent HD autopsy cohorts (n=751) to explore the frequency of CNP and their associations. Neuropathologic data from brains with a pathological diagnosis of HD from the New York Brain Bank (discovery, n=132) and the personal files of one of the authors (replication, n=619). Brains followed a standardized protocol of at least 14 blocks. HD brains with Alzheimer disease neuropathologic change (ADNC), Lewy body disease (LBD), and FTLD/ALS were deemed CNP. In the discovery cohort, 19.7% of individuals had CNP (16.7% ADNC, 3.8% LBD, 1.5% ALS). Likewise, 20% of HD brains in the replication cohort had CNP. CNP were more common in older individuals with lower CAG repeat expansions and pathologic grade than those with pure HD. No significant difference between the CAG-age product (CAP) score was found in pure HD versus those with CNP. Collectively, ALS co-occurred in 6 HD brains (0.8%), two of which were immunostained and found to harbor both TDP-43 and HTT aggregates. One HD brain in the replication cohort had FTLD-tau. The frequency of ALS in HD appears greater than that reported in population datasets (0.006%). CNP is frequent in older HD patients with lower CAG repeat expansions. Consistent with prior reports, ALS is more frequent in HD than expected and suggests genetic pleiotropy in pathogenic HTT repeat expansion. 1. Dewan R, Chia R, Ding J, Hickman RA, Stein TD, et al. Neuron. 2021 Feb 3;109(3):448-60. PLATFORM 2: Muscle/Nerve, Inflammatory 9 Epidermal SIRT1 Modulates Mechanical Allodynia in Diabetic Neuropathy Cheng-Ying Ho1, Jennifer Holler1, Mohammad Salimian2, Yanni Kevas1, Julianna Remark3, Catherine Lu3, Krish Chandrasekaran1, James Russell1 1University of Maryland; 2Orlando Health; 3New York University Introduction: Diabetic neuropathy (DN) is a debilitating disorder characterized by sensory loss and pain. Although common, DN has no effective treatment. A notable pathologic finding of DN is loss of sensory apparatus in the skin, causing sensory abnormalities and pain. Given that diabetic patients frequently develop skin complications, we hypothesize that skin microenvironment is important for the pathogenesis of DN. Methods: Our investigation focused on a skin molecule epidermal sirtuin 1 (SIRT1), which is an NAD+-dependent deacetylase known to regulate metabolism and senescence. To address the role of epidermal SIRT1 in neuroprotection against DN, we created a tamoxifen-inducible epidermal SIRT1 knockout (KO) and a doxycycline-inducible epidermal SIRT1 overexpression (OE) mouse model. The KO and control mice were placed on high-fat diets (HFDs), and were subsequently assessed by behavioral, morphologic and transcriptome analyses. SIRT1 overexpression was induced in mice after three months of HFDs. Results: The DN phenotype was greatly exacerbated by depletion of epidermal SIRT1, as mice developed extreme mechanical allodynia after HFD. There was also evidence of large-fiber neuropathy, including loss of Meissner corpuscles, tail sensory nerve conduction defects and degeneration of large-diameter axons, while small nerve fibers and the corresponding nociception were largely intact. The phenotype could not be rescued by treatment with the NAD+ precursor nicotinamide riboside. In comparison, induction of epidermal SIRT1 overexpression alleviated the diabetic mechanical allodynia in mice. One potential mechanism of achieving epidermal SIRT1-mediated neuroprotection is increasing the expression of epidermal brain-derived neurotrophic factor (BDNF), which could preserve the morphologic and functional integrity of Meissner corpuscles. Conclusions: Our data suggest an important role of epidermal SIRT1 in maintaining skin sensory apparatus and preventing mechanical allodynia in the setting of diabetes. The findings also highlight epidermal SIRT1 as a promising therapeutic target for DN due to easy accessibility of SIRT1 in skin keratinocytes. 10 Neuromuscular Pathology in Congenital Onset, Fatal Hereditary Spastic Paraplegia (SPG61) due to ARL6IP1 Pathologic Variants Nicole Becker1, Karra Jones1, Steven Moore1 1University of Iowa Department of Pathology This case reports on the light microscopic and ultrastructural pathology in the muscle and nerve biopsies from a patient with hereditary spastic paraplegia due to pathologic variants in the ARL6IP1 gene (SPG61). The biopsies are from a 5-month-old boy who presented at birth with hypotonia, respiratory distress, and weak suck reflex. At the time of biopsy, SMN1 testing had failed to identify a pathogenic variant. Chromosomal microarray showed 7.7% homozygosity, consistent with consanguinity. On physical exam, he had weak head control, absent distal extremity movement, and absent deep tendon reflexes. The quadriceps muscle exhibited grouped muscle fiber hypertrophy and hypotrophy in the pattern of classic spinal muscular atrophy. Intramuscular nerve twigs contained only rare myelinated axons. Myelinated axons were absent from the sural nerve biopsied at the ankle; ultrastructural evaluation revealed numerous bands of Büngner. Subsequent whole exome sequencing identified homozygous pathologic nonsense variants in the ARL6IP1 gene, c.346C>T, p.R116*. This gene encodes for ADP-ribosylation-like factor 6-interacting protein 1, a tetraspan membrane protein composed of highly conserved hydrophobic hairpin domains. The protein is implicated in the formation, structural maintenance, and function of the endoplasmic reticulum. The neuropathologic abnormalities associated with pathogenic variants in this gene have only rarely been described in the literature. Prior cases with the same or similar truncation variants in ARL6IP1 survived from 4 months to at least 12 years (Cao Y et al., Clinical Genetics. 2020:1-4). Our patient and his affected sibling died at 28 and 7 months, respectively. This case demonstrates congenital onset of severe sensorimotor neuropathy (or perhaps neuronopathy) in hereditary spastic paraplegia, SPG61. 11 Novel Variants in the Riboflavin Transporter Gene SCL52A2 Associated With Progressive Axonal Sensorimotor Neuropathy Angus Toland1, Michael Lopez2, Han Phan2, Hannes Vogel1 1Stanford University; 2University of Alabama at Birmingham and Children's Hospital of Alabama A 7-year-old female was initially diagnosed at 1 year of age with axonal Guillain-Barré syndrome based on nerve conduction/electromyography and cerebrospinal fluid albuminocytological dissociation. After 6 years, she progressed to include respiratory failure and dysphagia in spite of treatment for presumed chronic inflammatory demyelinating radiculoneuropathy. The neurological examination demonstrated normal intellect with generalized facial and extremity weakness. The weakness was proximal and distal with upper extremities more severely affected. Myostatic reflexes were absent in upper extremities and trace at the patella. Sensation was diminished in a non-length dependent manner. ANA panel, heavy metals, inflammatory markers, serum and urine protein electrophoresis, and urine porphobilinogen were unremarkable. Serum vitamin B2 and acyl-carnitine profiles were also normal. NCS/EMG testing showed a severe and generalized axonal polyneuropathy. Genetic testing demonstrated two variants of uncertain significance (VUS) in trans in the SCL52A2 gene encoding the riboflavin transporter. The variants of uncertain significance in SCL52A2 were c.1025T>C (p. L342P) and c.449G>A (p. G150D). Both variants are at highly conserved residues and not reported in normal databases (ExAC or gnomAD). Vastus lateralis muscle biopsies showed advance non-selective atrophy with marked fiber type grouping and numerous overly-dark fibers by esterase enzyme histochemistry. Sections of the sural nerve demonstrated moderate loss of myelinated fibers with occasional regenerative clusters and foci of Wallerian degeneration. She began empiric high dose riboflavin therapy and experienced incremental improvement. Riboflavin transport deficiency (RTD) due to homozygous or compound heterozygous mutations in the transporter gene SCL52A2 have been reported as rare causes of amyotrophic lateral sclerosis-like syndrome responsive to high-dose oral riboflavin supplementation. The putative mechanism of neurodegeneration is reported to be secondary to mitochondrial dysfunction. Our case reports novel VUS which likely account for a rare pediatric presentation of axonal, sensorimotor polyneuropathy with bulbar involvement that represents a treatable condition. 12 COVID-19-Associated Immune-Mediated Necrotizing Myopathy: A 3-Case Series Daniel Sullivan1, Calixto-Hope Lucas1, Dorukhan Bahceci1, Biswarathan Ramani1, Henry Sanchez1, Marta Margeta1 1University of California-San Francisco Symptomatic infection with SARS-CoV-2 (COVID-19) affects multiple organ systems including skeletal muscle; elevated creatine kinase levels are reported in up to 30% of cases. However, the nature of COVID-19-associated muscle injury has not been studied in detail to date. Here, we report histologic findings in three cases of necrotizing myopathy following infection with SARS-CoV-2. In this study, we examined three skeletal muscle samples from patients with confirmed recent (1-4 months) COVID-19 diagnoses and either remote or concurrent history of statin use. Two specimens were thigh muscle biopsies submitted for evaluation of rhabdomyolysis, while the third was psoas muscle sampled during autopsy of a patient who died from COVID-19 pneumonia. All cases showed similar findings, with abundant necrotic and regenerating fibers (20-50% of total) and no endomysial lymphocytic inflammation. Immunohistochemistry for autophagic markers LC3 and p62 showed frequent fibers with dense sarcoplasmic puncta in all cases. The two biopsy samples (for which frozen tissue was available) also demonstrated diffuse upregulation of MHC1 in muscle fibers and complement C5b9 deposition in the sarcolemma of viable fibers. Dystrophic calcifications were present in two cases. Ultrastructural analysis by electron microscopy was performed on one biopsy sample and did not demonstrate SARS-CoV-2 viral particles; reflex immunohistochemistry for SARS-CoV-2 was negative. Laboratory testing for anti-SRP was performed for the two biopsy cases and was negative; anti-HMG-CoA-reductase was performed for one case and was also negative. These findings indicate that some patients with COVID-19 develop a severe immune-mediated necrotizing myopathy either concurrently or after presenting with other COVID-19 symptoms, suggesting a para/postinfectious immune-related mechanism of muscle damage rather than direct viral toxicity; a similar pattern of muscle injury was observed in limited studies of SARS cases from early 2000s. Additional research is necessary to evaluate the specific mechanism and risk factors that elicit this immune-mediated response. 13 Characterization of Cerebrospinal Fluid Immune Cell Types in Neuroinflammatory Conditions Using Single-cell RNA Sequencing Tina Roostaei1, Claudiu Diaconu1, Hanane Touil1, Dheeraj Malhotra2, Claire Riley1, Vilas Menon1, Philip De Jager1 1Columbia University Irving Medical Center; 2F. Hoffmann-La Roche Ltd Immune cells play an important role in the pathogenesis of neuroinflammatory disorders. Single-cell RNA-sequencing (scRNA-seq) provides new means for discovery and characterization of immune cell types and states by simultaneous measurement of expression levels of thousands of genes. Here, we investigated the immune cell composition of cerebrospinal fluid (CSF) as the most accessible immune compartment in contact with the central nervous system, by performing scRNA-seq on 27 fresh CSF samples collected at the time of diagnostic lumbar puncture for suspected neuroinflammatory conditions (13 untreated and 6 treated multiple sclerosis, and 8 other neuroinflammatory disorders including optic neuritis, transverse myelitis, migraine, and neurosarcoidosis). After removing doublets, RBCs, and low-quality cells, 64,106 cells remained for analysis. Top-level clustering identified distinct clusters for CSF major cell types: T-cells (86%), myeloid cells (10%), NK-cells (2%), B-cells (1%), plasma-cells/plasmablasts (0.5%), plasmacytoid-DC (0.5%). Mapping our cells to the Azimuth peripheral blood CITE-seq atlas suggested that: neuroinflammatory CSF T-cell compartment mainly consisted of CD4+T-central memory (52%), CD8+T-effector memory (20%) and CD4+T-naïve (9%); B-cells consisted of B-intermediate (56%), B-memory (38%) and B-naïve (6%); and 50% of NK-cells were CD56bright. As previous scRNA-seq studies comparing blood and CSF had shown additional microglia-like clusters only present in CSF, we further characterized our myeloid cells in reference to two extra human scRNA-seq datasets: (1) Villani dataset of peripheral monocytic and dendritic-cells, (2) our published brain microglia dataset (16,242 cells). Our findings suggested that CSF myeloid cells mostly consisted of cells resembling microglia-cluster1 (homeostatic microglia, 30%) microglia-cluster8 (cells with low RNA content and down-regulated transcription factors, 29%), CD1C+ DC (23%), and monocytic cells (12%). Our data offer a new level of resolution in cell populations present in CSF (including detailed characterization of 19 T-cell and 11 myeloid clusters) and can be leveraged in further mechanistic studies on the pathophysiology of neuroinflammatory disorders. 14 In Situ Transcriptome Analysis Of The Brainstem During Systemic Inflammatory States Daniel Marker1, Clayton Wiley1 1University of Pittsburgh Medical Center There can be significant cognitive consequences associated with systemic infection, immune effector therapy, or autoimmune disease. Acute alteration of mental status followed by long-term cognitive deficits can occur in absence of definitive radiologic or neuropathologic abnormalities and may reflect peripheral cytokine induced neuronal dysfunction. While in vitro and in vivo animal models have made some progress identifying potential neuroprotective therapeutic targets, meaningful evaluation of human tissues has been lacking. We leveraged the emerging technology of digital spatial profiling (DSP)-based transcriptomics to assess changes in inflammatory gene expression in the human brainstem. Briefly, DSP allows assessment of gene expression in microscopically defined regions of interest directly on formalin fixed paraffin embedded sections. We utilize this technology to discover the expression of inflammatory genes in brainstem tissue using routine autopsy tissues. Differentially expressed genes were then targeted for traditional immunohistochemical and in situ hybridization studies. We examined cases of sudden death (normal control), bacterial sepsis, and patients treated with cell based immune effector therapy (CAR-T). DSP discovered altered gene expression in the cases of systemic inflammation compared to control cases of sudden death. The gene expression profiles differed by the etiology of the inflammatory state. Interestingly, there were also gene expression differences between peripheral cerebrospinal fluid-exposed brainstem and central brainstem within the same tissue section. Differential expression of select genes was confirmed by dual-color in situ hybridization. These data provide interesting insights on the effect of systemic inflammatory states on the central nervous system transcriptome and provide a basis for potential therapeutic intervention. 15 A Clinicopathologic Outcome Study of CNS Post-transplant Lymphoproliferative Disorder (PTLD) Ekin Guney1, Calixto-Hope Lucas1, Melike Pekmezci1, Sanda Alexandrescu2, Bret Mobley3, Serguei Bannykh4, Susanne Powell5, Angus Toland6, Hannes Vogel6, Christian Davidson7, Kristian Schafernak8, Janna Neltner9, Daniel Boué10, Robert Ohgami1, Andrew Bollen1, Tarik Tihan1, Arie Perry1, David Solomon1, Kwun Wah Wen1 1University of California San Francisco; 2Boston Children's Hospital, Harvard Medical School; 3Vanderbilt University Medical Center; 4Cedars-Sinai Medical Center; 5Houston Methodist Hospital; 6Stanford University Medical Center; 7University of Utah Health; 8Phoenix Children’s Hospital; 9University of Kentucky Chandler Medical Center; 10Nationwide Children's Hospital and The Ohio State University Background: Post-transplant lymphoproliferative disorder (PTLD) is a significant complication of organ transplants. Destructive PTLDs can be polymorphic (P-PTLD) or monomorphic (M-PTLD). Methods: The clinicopathologic features of 19 M-PTLD and 6 P-PTLD of the CNS were retrospectively studied. Results: Twenty-one patients received solid organ transplants (most commonly kidney n= 14, followed by liver, n = 8) and 3 were bone marrow recipients. Strikingly, 23 patients had isolated CNS PTLD lesions and 2 also had gastrointestinal involvement. Disease was predominantly multifocal (n= 15, 60%) with supratentorial (100%) and rare infratentorial (n=2, 8%) involvement. Five patients (25%) were treated with chemoradiotherapy and 15 (75%) were treated with chemotherapy only. M-PTLD patients demonstrated a median survival (MS) of 122 months, while P-PTLD patients did not reach MS at 145 months. Pathologically, all cases exhibited perivascular and parenchymal involvement with neoplastic cells showing variable nuclear-to-cytoplasmic ratios. Other than two M-PTLD, majority of the cases (92%) were Epstein-Barr virus (EBV)-positive. Almost all M-PTLD cases (18/19; 95%) showed DLBCL morphology, whereas one was marginal zone lymphoma type. Of the DLBCL type with available IHC stains (n = 11), 91% were of non-germinal center (Non-GC) origin and only one case was of germinal center GC origin (9%). Seven cases (64%) were non-double protein expressor (non-DPE) and four (36%) were DPE. Hodgkin/Reed-Sternberg (HRS)-like cells were present in 5 (26%) M-PTLD. All P-PTLD cases were EBV-positive and 40% contained HRS-like cells. Conclusions: CNS PTLD were highly enriched for EBV and non-GC (in cases of M-PTLD DLBCL type). M-PTLD demonstrated a median survival (MS) of 122 months while P-PTLD patients did not reach MS at 145 months. 16 Elevated Oxidative Stress and DNA Damage in Cortical Neurons of Chemotherapy Patients Matthew Torre1, Adwitia Dey1, Jared Woods1, Mel Feany1 1Brigham and Women’s Hospital and Harvard Medical School, Boston, MA Background: Up to 80% of cancer patients treated with chemotherapy develop deficits in cognitive domains including memory and executive functioning. This clinically underrecognized phenomenon, termed chemotherapy-related cognitive impairment (CRCI), contributes to significant morbidity. To better understand potential mechanisms underlying the neurotoxicity of chemotherapy, we evaluated markers of oxidative stress and DNA damage in frontal lobe cortical neurons of cancer patients treated with chemotherapy compared to control patients. Design: We reviewed our institution’s autopsy archives for cancer patients treated with chemotherapy, cancer patients who did not receive chemotherapy, and patients without history of cancer (or chemotherapy). FFPE sections of frontal lobe from these three patient cohorts were stained for markers of oxidative stress (nitrotyrosine and 4-hydroxynonenal (4-HNE)) and DNA damage (pH2AX and pATM) using routine immunohistochemistry/immunofluorescence. Two-hundred cortical neurons were evaluated per stain per case. The average percent of positive cortical neurons per cohort for each marker was calculated. Comparisons between cohorts were performed using one-way ANOVA with the Holm-Sidak’s multiple comparisons test. Results: Cancer patients treated with chemotherapy (n=15) had a higher percentage of nitrotyrosine-positive cortical neurons (63.4%) compared to controls (cancer patients without chemotherapy (n=10), 43.3%, p<0.01; patients without cancer (n=10), 49.3%, p<0.05) and a higher percentage of 4-HNE-positive neurons (48.0%) (cancer patients without chemotherapy, 33.3%, p<0.05; patients without cancer, 35.9%, p=0.057). In addition, cancer patients treated with chemotherapy had a higher percentage of cortical neurons with pH2AX-positive foci (28.8%) compared to controls (cancer patients without chemotherapy, 12.8%, p<0.01; patients without cancer, 16.2%, p<0.05) and a higher percentage of pATM-positive neurons (80.0%) (cancer patients without chemotherapy, 38.3%, p<0.05; patients without cancer, 38.0%, p<0.05). Conclusions: Cancer patients treated with chemotherapy have elevated markers of oxidative stress and DNA damage in frontal lobe cortical neurons, suggesting that these pathways may be relevant to the pathophysiology of CRCI. PLATFORM 3: Glial Tumors 17 Common Glial Progenitor Signature is Predominantly Recapitulated Across GBMs and Enriched Within the Infiltrative Edge Zarmeen Mussa1, Susana Ramos1, Kristin Beaumont1, Robert Sebra1, Alexander Tsankov1, Nadejda Tsankova1 1Icahn School of Medicine at Mount Sinai Glioblastoma (GBM) cells exploit developmental programs to sustain their proliferation and infiltration. However, the relationship between these programs and fetal gliogenesis remains poorly understood due to insufficiency of data from late gestation, when glial proliferation and migration increase. We generated a comprehensive single nuclei RNA sequencing (snRNA-seq) dataset of approximately 180,000 nuclei taken from the germinal matrix and the cortical plate of 15 neurotypic fetal postmortem samples, ranging from 17 to 41 gestational weeks, capturing prenatal gliogenesis with high spatiotemporal resolution. Through unbiased clustering and differential expression analyses, we identified several neuronal and glial progenitor populations, some transiently present during fetal development and absent in adult, and defined their signatures across both regions and four developmental stages. Lineage inference and directionality analyses highlighted a distinct intermediate glial population (GPC/g-IPC), marked by EGFR expression, that appears to be a common progenitor to both oligodendrocyte progenitor cells (OPC) and astrocytes (AC). We then sequenced the transcriptiome of approximately 62,000 nuclei taken from the core and infiltrating edge of six surgically resected GBM samples with diverse genomic alterations, associated with classical, proneural, and mesenchymal subtypes. Unbiased clustering revealed distinct neoplastic and non-neoplastic populations within each GBM sample which, when integrated, clustered by cell-type, irrespective of patient origin. Projecting our previously defined developmental cell type signatures onto the integrated GBM clusters revealed enrichment of GPC (43%), AC (19%), transit amplifying (14%), and outer radial glia (10%)-like cells in tumor clusters, with minor contributions from neurogenic progenitor (6%) and OPC (2%) -like cells. Relative to tumor core, glioblastoma cells within the infiltrative edge displayed greater GPC signature enrichment, irrespective of the tumor’s genomic alterations. Developmental states are driven by potentially targetable regulatory networks and resolving their unique contribution within GBM’s infiltrative niche may provide new avenues for anti-invasive therapy. 18 H3F3A G34 Mutation Frequency in High-grade IDH-wildtype Diffuse Glioma in Adult Patients Jorge Trejo-Lopez1, Corinne Praska1, Cinthya Zepeda Mendoza2, Thomas Kollmeyer1, Asha Nair1, Aditya Raghunathan1, Caterina Giannini1, Rachael Vaubel1, Aivi Nguyen1, Mark Jentoft1, Kliment Donev1, Gang Zheng1, Margaret DiGuardo1, Benjamin Kipp1, Robert Jenkins1, Cristiane Ida1 1Mayo Clinic; 2University of Utah According to cIMPACT-NOW update 6, IDH-wildtype diffuse glioma (IDHWT-DG) harboring a missense mutation involving codon G34 of histone H3.3 protein (H3.3_G34-DG) should be included in future WHO CNS tumor classification. H3.3_G34-DG occurs in young adults, partially overlapping with the lower age range of adult-type IDH-wildtype glioblastoma (IDHWT-GBM). Herein, we estimate the H3F3A G34 mutation frequency in a series of adult high-grade IDHWT-DG to assess how often an H3.3_G34-DG might be misclassified as IDHWT-GBM based solely on a negative IDH result. Cases included 952 unique patients ≥18 years with IDHWT-DG showing microvascular proliferation and/or necrosis who underwent clinical testing (2017-2020) using a 50-gene mutation (n=193) or 219-gene mutation and fusion (n=759) targeted NGS panel (including H3F3A, HIST1H3B, HIST1H3C, IDH1 and IDH2), and chromosomal microarray (n=375). Twelve H3F3A G34 mutations (11 G34R, 1 G34V) were identified. Median age was 24.5 years (range, 18-50). H3F3A G34 mutation frequency was 1.3% (12/952), being 4.3% (12/282) in patients 18-50 years and 0% (0/670) in patients >50 years. All H3.3_G34-DG tumors were supratentorial non-midline, frequently showing primitive morphology (58%; 7 of 12). Clinically relevant ATRX mutations were detected in all 12 cases, frequently associated with loss of expression by immunohistochemistry (8 complete loss, 3 partial loss and 1 preserved expression). Additional recurrent abnormalities included mutations in TP53 (n=11) and PDGFRA (n=9). All evaluated cases (n=4) had complex genomes with partial to whole-arm gains and losses overall distinct from IDHWT-GBM. In conclusion, H3F3A G34 testing should be considered for 18-50 year-old patients, particularly in cases showing primitive morphology and/or loss of ATRX expression, while the negligible frequency of H3F3A G34 mutation in high-grade IDHWT-DG among patients >50 years indicates that tumors in this age group may be classified as IDHWT-GBM following a negative IDH result without additional H3F3A G34 testing, especially if ATRX protein expression is preserved. 19 The Ketogenic Diet is Ineffective in Preclinical Models of IDH1 Wild-type and IDH1 Mutant Glioma Craig Horbinski1, Rodrigo Javier1 1Northwestern University Despite decades of intensive research, infiltrative gliomas are still usually lethal and challenging to treat. A subset of gliomas contains mutations in isocitrate dehydrogenase 1 (IDH1mut), which disrupts cellular biochemistry; such gliomas are generally less aggressive than their IDH1 wild-type (IDH1wt) counterparts. Some preclinical studies have suggested that a ketogenic diet (KD), characterized by low-carbohydrate and high-fat content, may be beneficial against a variety of cancers, including gliomas. However, not all studies have shown promising results, and to date, no study has addressed the sensitivity of glioma cells to KD in the specific context of the endogenous IDH1mut metabolic landscape. The aim of the current study was to compare the effects of KD in preclinical models to IDH1wt versus IDH1mut gliomas. In vitro treatment of patient-derived IDH1wt and IDH1mut glioma cells with the ketone body β-hydroxybutyrate showed no significant effect on cell proliferation in a low glucose culture environment. Likewise, the in vivo flank growth rates of these patient-derived IDH1wt and IDH1mut glioma xenografts showed no significant difference when mice were fed KD versus regular diet (GBM12 P=0.98, GBM164 P=0.4, GBM196 P=0.11). Finally, KD had no effect on the survival of mice orthotopically engrafted with isogenic Sleeping-Beauty transposase-engineered IDH1wt (median survival 22 days for control versus 23 days for KD, P=0.23) or IDH1mut glioma cells (median survival 26.5 days for control versus 26 days for KD, P=0.81). These data suggest that IDH1mut gliomas are not inherently more responsive than IDH1wt gliomas to KD, and that clinical trials further exploring KD in this subset of glioma patients are probably not warranted. 20 Single Nucleus RNA Sequencing Identifies Cell Type Specific Alterations At the Margin of Glioma Osama Al-Dalahmah1, Aayushi Mahajan1, Jeffrey Bruce1, Vilas Menon1,Peter Canoll1 1Columbia University Irving Medical Center Glioblastoma is an aggressive diffusely infiltrating brain malignancy. Glioma cells at the infiltrative margins that escape surgical resection give rise to recurrence and are the target of adjuvant therapy. Furthermore, glioma-margins contain a diversity of non-neoplastic brain cells, including astrocytes and myeloid cells, which may contribute to disease progression. Characterizing the abundance and transcriptional alterations of the different cell types at the margins of glioblastoma remains an important challenge. To this end, we performed single-nucleus RNA-sequencing of surgical samples from cores and margins of glioblastomas and identified clinically relevant transcriptional signatures. While most nuclei from glioma-core samples harbored copy number variations (CNV+), indicative of transformed cells, most nuclei from the glioma-margin samples were CNV-. Unbiased clustering identified six CNV+ glioma-states and fourteen CNV- cell types with distinct lineage-specific signatures. Survival analysis revealed that enrichment of gene signatures from both CNV+ and CNV- clusters significantly influenced survival. Interestingly, untransformed astrocytes expressed genes previously incriminated in glioma prognosis, poor survival, and resistance to therapy, identifying astrocytes as potential drivers of disease progression. Deconvolution of bulk-transcriptomics from spatially localized samples resolved the landscape of cellular phenotypes spanning from core to margin and demonstrated that untransformed astrocyte and glioma cells showed reciprocal patterns of abundance. Indeed, gene expression analysis revealed that glioma margin samples were predominantly enriched for untransformed astrocytes signature and depleted for glioma gene signature. Notably, untransformed astrocytes and microglia/myeloid cells were enriched for neurodegenerative gene signatures, revealing common alterations across different neurological diseases. 21 Computational Algorithm Predicts cIMPACT-NOW Glioma Diagnoses and Molecular Classifications from Frozen Section MacLean Nasrallah1, Junhan Zhao2, Cheng Tsai2, David Meredith3, Jeffrey Golden4, Kun-Hsing Yu5 1University of Pennsylvania; 2Harvard Medical School; 3Brigham and Women's Hospital; 4Brigham and Women's Hospital and Cedars-Sinai Medical Center; 5Harvard Medical School and Brigham and Women's Hospital Intra-operative diagnosis and grading of gliomas, crucial for guiding surgery, can be difficult. In addition to verifying the presence of lesional tissue to guide extent of surgery, understanding the subtype of glioma, including grade and molecular features, is increasingly necessary to guide treatment and allocation of fresh tissue. Treatment may include intra-operative therapy, as clinical trials have begun to utilize intra-operative components. Furthermore, the ability to predict molecular changes intraoperatively could provide opportunities for novel clinical trials. To achieve intraoperative diagnostics that could assist in guiding treatments and clinical trials, we developed machine learning approaches to diagnose the digitized slides from two institutions (n=223 from Brigham and Women’s Hospital; n=148 from the University of Pennsylvania) and digital images from The Cancer Genome Atlas (n=1131). Matched whole-exome or targeted sequencing results were utilized to develop molecular predictions. Our algorithm utilizes transfer learning methods to enable high-performance convolutional neural networks for different histology and molecular classification tasks, with fine-tuning for enhancing the models’ generalizability. Our models identify glioma histologic grades defined by 2016 WHO Classification (patient-level Accuracy: 0.887 ± 0.056, AUC: 0.959 ± 0.041). In addition, our models identify IDH mutational status (patient-level Accuracy: 0.793 ± 0.038, AUC: 0.878 ± 0.03). Finally, our models subclassify IDH-mutant gliomas according to cIMPACT-NOW updates (patient-level Accuracy: 0.834 ± 0.041, micro-average AUC: 0.895 ± 0.045, macro-average AUC: 0.875 ± 0.065), defined as Class 1: Oligodendroglioma with IDH1 or IDH2 mutation and 1p/19q codeletion, Class 2: Astrocytoma with IDH1 or IDH2 mutation and TP53 mutation, Class 3: Astrocytoma with IDH1 or IDH2 mutation, TP53 mutation, and CDKN2A or CDKN2B homozygous deletion, and Class 4: Glioblastoma with IDH1 or IDH2 mutation. These results suggest deployment of deep learning on frozen section tissue can contribute to intraoperative diagnostics, providing an opportunity for early and novel clinical trials in gliomas. 22 Targeting ATR and the ERK Pathway in High-grade Solid Tumors with Concurrent NF1 and ATRX Loss Ming Yuan1, Christine Pratilas1, Jaishri Blakeley1, Christine Davis1, Alan Meeker1, Christopher Heaphy2, Fausto Rodriguez1 1Johns Hopkins University School of Medicine; 2Boston University Neurofibromatosis type 1 (NF1) is an inherited genetic syndrome characterized by the development of benign and malignant tumors affecting the central and peripheral nervous systems. Prior work from our laboratory has uncovered a high frequency of ATRX alterations and the alternative lengthening of telomeres (ALT) in subsets of NF1-associated glioma, as well as malignant peripheral nerve sheath tumors (MPNST). Preclinical work by others has uncovered a biologic vulnerability of ALT positive cells (which are proficient in homologous recombination) to ATR inhibition, a regulator of homologous recombination. To identify the biologic relevance of ATRX loss in NF1-associated tumorigenesis we studied the phenotype of combined NF1 and ATRX deficiency in glioma and MPNST. For these experiments we used NF1-deficient sporadic glioblastoma cell lines (U251, SF188), a NF1-associated ATRX mutant glioblastoma cell line (JHH-CRC64), and two NF1-deficient MPNST cell lines (ST88-14, NF90-8). Cells were treated with ATR inhibitors (AZD6738 and VE-822) and a MEK inhibitor (AZD6244). ATRX knockout (KO) and TERC knockout (KO) led to ALT-like properties and sensitized U251 cells (but not SF88) to ATR inhibition (AZD6738 and VE-822) but not MEK inhibition (AZD6244). Similar effects were noted using MPNST cell line NF90-8 after ATRX knockdown/TERC KO (but not in ST88-14). JHH-CRC64 cell line demonstrated sensitivity to AZD6244 (MEK inhibition) but not AZD6738 (ATR inhibition). Our study supports the feasibility of targeting ATR and ERK pathways in subsets of NF1-deficient and associated tumors, but further investigation into the variable responses is warranted. 23 Multiple Lines of Evidence for Chromosomal Instability as an Underlying Factor in Malignant Behavior in Astrocytoma Subsets Timothy Richardson1, Kalil Abdullah2, Mariano Viapiano3, Kanish Mirchia3, Matija Snuderl4, Kimmo Hatanpaa2, Jamie Walker1 1UT Health San Antonio; 2UT Southwestern Medical Center; 3SUNY Upstate Medical Center; 4NYU Langone Health Chromosomal instability (CIN) is an underlying mechanism for tumorigenesis and malignant progression in a wide variety of cancers, perhaps best characterized with the APC mutation in colorectal carcinoma. The effect of this process in brain tumors is less understood, with relatively few studies examining the effects of CIN, chromothripsis, and mutations in genes with primary functions related to the maintenance of overall genomic stability. Here, we use multiple converging techniques to investigate indirect and direct lines of evidence for the presence and impact of chromosomal instability in large institutional and publicly-available IDH-mutant and IDH-wildtype astrocytoma cohorts. These data demonstrate that IDH-mutant astrocytomas undergo progressive destabilization of the genome with mounting deleterious copy number variation (CNV) as these WHO grade II tumors progress to glioblastoma, and this molecular process frequently precedes traditional histologic hallmarks of higher grade and correlates to more aggressive behavior. Molecular signatures of CIN, including mRNA expression panels and mutations in genes known to be involved with the maintenance of chromosomal integrity are reflective of directly measured CNV. These findings correlate to clinical outcome as measured by Karnofsky performance status, recurrence/progression-free survival, and overall survival in both IDH-mutant and some IDH-wildtype cohorts. In addition, multiple small-scale single-cell sequencing studies, multi-region autopsy sequencing studies, and studies of recurrent tumors appear to directly confirm the presence of ongoing CIN in select IDH-mutant astrocytoma cases. In conclusion, we demonstrate that CIN in low-grade IDH-mutant gliomas is an early indicator of more rapid and aggressive progression and malignancy and further investigation may reveal therapeutic targets that leverage CIN in glioma. 24 Genome-wide Copy Number Alteration Signatures Reliably Predict IDH Mutational Status in Diffuse Astrocytic Gliomas Nicholas Nuechterlein1, Eric Holland2, Linda Shapiro1, Patrick Cimino3 1Computer Science & Engineering, University of Washington, Seattle, WA; 2Human Biology Division, Fred Hutchinson Cancer Research Center, Seattle, WA; 3Laboratory Medicine and Pathology, University of Washington, Seattle, WA Background: Diffuse astrocytic gliomas harboring mutations in IDH1/2 portend significantly better clinical outcomes than IDH-wildtype gliomas and knowledge of IDH mutational status is necessary to interpret any investigational study of diffuse gliomas. While DNA sequencing is the gold standard for determining IDH-mutational status, genome-wide methylation arrays and gene expression profiling have been used for surrogate mutational determination. Previous studies by our group suggest that IDH-mutational status can be predicted by genome-wide SNP-array derived somatic copy number alteration (SCNA) data alone, however a rigorous model to accomplish this task has yet to be established. Methods: In this study, we use genome-wide SCNA data from 634 diffuse astrocytic gliomas with known IDH mutational status in The Cancer Genome Atlas (TCGA) to train machine learning models to predict IDH mutational status. To determine model efficacy, we evaluate our models on a second cohort of 163 glioblastomas in the TCGA dataset whose IDH mutational status is inferred from whole-genome methylation patterns. We then apply these models to a cohort of REMBRANDT study subjects for whom SCNA data, but not IDH mutational status, is available. Results: We can differentiate IDH mutational status in our training set with cross-validated AUC=0.989±0.01. When evaluating our models on 163 additional glioblastomas with methylation-inferred IDH mutational status, we achieve an AUC=0.968. Finally, IDH-predictions on the REMBRANDT dataset show survival trajectories with similar overall survival (wildtype: 1.2 vs 1.1 years; mutant: 2.4 vs. 2.8 years) and hazard ratio (1.15 vs. 1.46) when compared to tumors in the TCGA. Conclusions: Using genome-wide SNP-array derived SCNA data, we successfully trained machine learning models to robustly predict IDH mutational status in diffuse gliomas. These models confidently assign IDH mutational status to tumor samples of retrospective diffuse glioma cohorts, such as the REMBRANDT study, whose participants have SCNA data but no IDH information. PLATFORM 4: Developmental/Pediatrics/Vascular 25 Developing Hindbrain Motor Neurons Show Spatial and Temporal Transcriptomic Diversity Mapping to Wiring Decisions Matthew Rose1, Alan Tenney2, Tammy Ray3, Daniel Creighton3, Alon Gelber2, Max Tischfield3, Evan Murray4, Tommy Collins3, Alicia Nugent5, Phillip Ang3, Sarah Izen3, Matthew Bauer5, Wentao Huang3, Rahul Satija6, Orit Rozenblatt-Rosen4, Evan Macosko4, Fei Chen4, Aviv Regev4, Elizabeth Engle3 1Harvard Medical School, Boston Children's Hospital, Brigham & Women's Hospital and Broad Institute; 2Boston Children's Hospital and Broad Institute; 3Boston Children's Hospital; 4Broad Institute; 5Harvard University and Boston Children's Hospital; 6New York Genome Center, New York University The brainstem ocular motor neurons (OMNs) mediate eye movements and are differentially affected in some disorders, compared with other motor neurons (MNs). In congenital cranial dysinnervation disorders (CCDDs) such as Duane Syndrome, OMN subpopulations show disrupted or aberrant innervation, while in Amyotrophic Lateral Sclerosis (ALS), OMNs continue to function while other MNs degenerate. Here we define unique gene expression patterns among developing MNs, and generate a toolbox of protocols and genetic markers to help study these disorders. We combine various mouse genetic reporter lines with intersectional temporal and spatial transcriptomics (bulk-, single cell-, and single nuclei RNA-seq, and Slide-seq) to isolate and compare eight distinct mouse MN populations from embryonic days E9.5-E18.5: the three ocular motor nuclei (CN3, CN4, CN6) and the other primary MN types (CN5, CN7, CN9/10, CN12 in brainstem, and spinal MNs). Gene expression was validated with database analysis, in situ hybridization, antibodies, and genetic axonal labeling. We correlate gene expression differences with cell age by both EdU labeling and tamoxifen-mediated temporal CreER induction, and visualize iDISCO- and EyeDISCO-cleared whole embryos by light sheet microscopy. Each MN population shows a unique genetic fingerprint, including novel markers of spatially- and temporally-distinct OMN subpopulations. Some OMN nerve branches correspond with cell birthdate and selectively contribute to specific aberrant branches in the Mafb-knockout mouse model of Duane Syndrome. Overall, this MN transcriptomic atlas uncovers distinct developmental gene expression patterns and markers of the various cranial motor neurons, and provides new tools to study their differential vulnerability in the CCDDs and other motor neuron disorders. 26 Neuropathology of Chiari Malformation II (CMII) with Chromosome X Alterations: An Autopsy Study in a 17-month-old Xi Wang1, Victoria Habet2, Nalin Leelatian1, Raffaella Morotti1, Sarah Kandil2, Armine Darbinyan1 1Department of Pathology, Yale School of Medicine; 2Department of Pediatrics, Yale School of Medicine Background: CMII is characterized by downward displacement of cerebellar tonsils, vermis and spinal myelomeningocele. Understanding the neuropathology of this rare condition is limited due to few autopsy reports. Here we present an autopsy study in a 17-month-old female patient with CMII and a structurally abnormal X chromosome (Turner syndrome variant). Clinical Presentation: The patient was born at 34 weeks and 5 days, with prenatal imaging diagnosis of myelomeningocele, CMII, ventriculomegaly and partial agenesis of corpus callosum (CC). She underwent myelomeningocele repair after birth, followed by Ventricular Peritoneal shunt placement. The hospital course was further complicated by vocal cord dysfunction requiring tracheostomy, and feeding difficulties. The patient was able to be discharged home but was readmitted months later and unfortunately passed away. Genetic Analysis: Exome sequencing showed an entire deletion of Xp and an entire duplication for Xq, (46, X, i(X)(q10)). No clinically significant variants among candidate genes for spina bifida were identified. Autopsy Findings: Postmortem examination showed a Luchenschadel skull, partial agenesis of the CC and the absence of the cingulate gyrus, descent of the cerebellum and brainstem associated with cerebellar hypoplasia, and elongation of the lower pons and the medulla. Microscopic examination showed decreased volume and structural anomalies of different regions of brain, including the insula and basal ganglia, diffuse gliosis in cerebrum and chronic ischemic changes in the brainstem. Focal segmental Purkinje cell loss and Bergman gliosis were identified in the cerebellum. Interestingly, syringomyelia was formed in the spinal cord, with a unique “dual column T-shaped” dilated central canal. Additional findings included aspiration pneumonia, tracheitis and peritonitis. Conclusion: We reported a rare case of CMII patient with structural chromosome X alteration, who survived 17 months after multiple surgeries and interventions. To our knowledge, this is the first report with this specific genetic alteration in CMII population. 27 A Pediatric Case of Lupus Cerebellitis Leyla Canbeldek1, Janina Markidan1, Cinthia Drachenberg1, Heather Ames1 1University of Maryland School of Medicine Lupus cerebritis is a rare but life-threatening complication of systemic lupus erythematosus (SLE). It is better understood and more often seen in adults, and presentation in pediatric patients is exceedingly rare. Here, we report a rare case of lupus cerebellitis in a pediatric patient. The patient is an 11-year-old male with a history of SLE for six years complicated by lupus nephritis. Additionally, he had an episode of suspected autoimmune demyelinating disease at age 4, resulting in total left-sided blindness. He has had long term immunosuppressive treatment including steroids, rituximab, mycophenolic acid, and hydroxychloroquine. The patient presented with a one-day history of severe headache and dizziness. MRI findings were suggestive of acute right cerebellitis with severe mass effect and edema causing obstructive hydrocephalus as well as tonsillar herniation. A stereotactic biopsy of the right cerebellum and dura mater was performed. Histologic sections showed acute hemorrhage, numerous macrophages, Purkinje cell loss, and Bergmann gliosis. Additionally, the vasculature showed mural inflammation with lymphocytes, fibrinoid necrosis, and neutrophilic dust as well as intravascular fibrin thrombi. Immunostaining showed dense C4d and IgG endovascular deposits. CD3 and CD20 immunostains showed a polytypic lymphocytic infiltrate. Additional staining for viral, bacterial, and fungal disease was negative. A diagnosis of lupus cerebellitis/cerebritis was made. He was treated with a course of steroids and rituximab and with a return to functional baseline in two weeks. Cerebellar involvement in systemic lupus erythematosus has rarely been described as one of the neurologic manifestations of this disease and is nearly absent from the pediatric literature. This case presented a specific challenge due to the presence of possible demyelinating disease and potential infectious or neoplastic complications of long-term immunosuppression. Lupus cerebritis/cerebellitis, though rare, should be considered in pediatric patients with a history of SLE presenting with new-onset neurologic deficits. 28 Pathologic Alexander Disease with Normal GFAP Sequencing Abigail Alexander1, Lauren Massingham2, Swee Lim3, Oliver Phillips3, Mary-Kathryn Chambers2, John Donahue1 1Department of Pathology and Lab Medicine, RI Hospital/Alpert Medical School; 2Division of Medical Genetics, Hasbro Children’s Hospital/Alpert Medical School; 3Department of Neurology, RI Hospital/Alpert Medical School Alexander Disease (AxD) is a rare and fatal neurodegenerative leukodystrophy characterized by eosinophilic protein aggregates (Rosenthal fibers) in astrocytes. Imaging reveals demyelination of major tracts within the cerebral cortex. It is caused by a heterozygous pathogenic variant in GFAP, the gene encoding for glial fibrillary acidic protein. Most cases are caused by de novo variants; however parent-to-child transmission has been described. There are four main subclassifications of AxD: neonatal, infantile, juvenile, and adult-onset. The neonatal, infantile, and juvenile types typically present in infancy or childhood with developmental delay or regression, megalencephaly, and failure to thrive. Adult-onset type presents in the 4th or 5th decade of life (range adolescence- adulthood) with a dysarthria, dysphonia, and/or ataxia. Some individuals may also have relapsing remitting hemiparesis. GFAP sequencing detects 98% of pathogenic variants in Alexander disease. Here, we describe a 58-year-old woman who initially presented after a fall and was found to have the hallmark symptoms of adult-onset AxD including acute onset of weakness and history of dysphagia. Imaging was also highly suggestive of AxD with brain MRI findings of profound volume loss with gliosis in the medulla, peri-dentate regions, and upper cervical cord. Family history was notable for “mobility concerns” in her mother and brother, raising concern for an autosomal dominant condition. Surprisingly, GFAP sequencing was normal. Additional ataxia molecular testing was also nondiagnostic. She died at age 62 without a diagnosis. At autopsy, there was an abundance of Rosenthal fibers observed in the medulla and spinal cord, indicating she had pathologic AxD. Possible explanations for nondiagnostic molecular testing include a mosaicism (GFAP change solely in her brain tissue), a nondetectable variant in GFAP such as cryptic splice site variant or a deletion/duplication, or change in another gene in the GFAP pathway causing Alexander disease. 29 Comprehensive Molecular Profiling of Pediatric CNS Malignancies: A Single-Institution Experience Using a Clinical Platform Michael Miller1, Helen Fernandes1, Susan Hsiao1, Mahesh Mansukhani1 1Department of Pathology and Cell Biology, Columbia University Primary CNS tumors in pediatric patients are rare and heterogeneous, and although it is challenging to predict their clinical behavior and establish targeted therapies, molecular integration may provide prognostic, predictive and perhaps diagnostic insight. A clinical whole-exome and transcriptome sequencing platform is used to characterize high risk or rare pediatric cancers at our institution, and since the establishment of this program over 500 pediatric cancers have been evaluated including 159 primary CNS tumors (e.g., 18 CNS-PNET, 35 medulloblastoma, 21 ependymoma, 76 glial/glioneuronal). Hierarchical clustering of the transcriptome data resulted in reasonably good segregation of known subgroups within medulloblastoma, ependymoma and CNS-PNET. This agnostic approach was not effective in segregating glial and glioneuronal tumors into previously known subgroups, with IDH-mutant glioma being an exception. This finding may reflect the molecular and histological heterogeneity of tumors within this category. A pitfall of clustering analysis for diagnostic purposes is that it requires a large mixed reference set. By leveraging publicly available gene-expression data (GSE64415, GSE85217) and calculating the relative enrichment of these genes in each tumor, transcriptome data can overcome this issue. Using this targeted (in silico) approach, non-WNT / non-SHH medulloblastoma and posterior fossa ependymoma were correctly sub-classified in a majority of cases. Applying a similar strategy to CNS-PNET tumors, two CNS ND-FOXR2 tumors and three C19MC-altered tumors were identified. Within the glial and mixed glioneuronal tumors, a cluster of astrocytic tumors, which harbored genetic alterations in RAS/RAF signaling and over-expressed CD34, may reflect PLNTY. While molecular profiling continues to play an important role in establishing targeted therapies, transcriptomic approaches may provide meaningful diagnostic and as a consequence prognostic information. This is particularly relevant to a subset of pediatric CNS malignancies that are believed to be driven by epigenetic alterations instead of single driver mutations. 30 Ultrastructural Assessment of the Filum Terminale in Tethered Cord Syndrome Patients with Ehlers-Danlos Syndrome Comorbidity Abigail McElroy1, John Donahue2, Thomas Brinker3, Petra Klinge1 1Rhode Island Hospital, Department of Neurosurgery; 2Rhode Island Hospital, Department of Pathology; 3Medical School Hannover, Department of Neurosurgery Objective: The filum terminale (FT) is collagenous structure hypothesized to act as a spinal cord stabilizer. Tethered cord syndrome (TCS) occurs secondary to an abnormally inelastic FT, leading to stretch induced injury to the spinal cord. Clinically, TCS is observed in the Ehlers-Danlos syndrome (EDS) population; however, the etiology of TCS in this population is poorly understood. This study sought to use transmission electron microscopy to examine the ultrastructure of collagen in the FT of TCS patients with and without EDS. Methods: Transmission electron microscopy was performed on FT specimens from 79 EDS-TCS and 10 TCS patients obtained during de-tethering surgery. Specimens were evaluated in longitudinal and cross-section and were assessed for collagen fibril structural abnormalities such as fibril disorganization and variation in fibril diameter in cross-section. Specimens were additionally assessed for collagen fibril microdamage such as kinking of the collagen fibrils and loss of D-period banding. Results: Structural abnormalities such as fibril disorganization (69.6% EDS-TCS; 10.0% TCS) and variation in fibril diameter (40.5% EDS-TCS; 11.1% TCS) were significantly (p<.001) more prevalent in the EDS-TCS population. Collagen fibril microdamage such as kinking fibrils (63.3% EDS-TCS; 30.0% TCS) was significantly more prevalent in the EDS-TCS population (p<.05). Loss of D-period banding (68.4% EDS-TCS; 30.0% TCS) was significantly more prevalent in the EDS-TCS population (p<.01). Conclusion: Prior studies have attributed fibril disorganization and variation in diameter to EDS, while loss of D-period banding and kinking of the fibrils is attributed to mechanical overload. While non-EDS TCS patients with low-lying conus have a FT of insufficient length to buffer traction forces, in EDS it is theorized that congenital abnormalities including hypermobility of the spine and congenital collagen fibril pathology, may serve as pathogenic factors exposing the FT to elevated traction forces and leading to the clinical presentation of TCS. 31 Effect of Cerebrovascular Pathology on the Relation Between Lewy Bodies and Parkinsonism Signs in Older Adults Sonal Agrawal1, Sue Leurgans1, Sukriti Nag1, Lisa Barnes1, David Bennett1, Aron Buchman1, Julie Schneider1 1Rush Alzheimer's Disease Center, Rush University Medical Center, Chicago Introduction: Our earlier studies report that Lewy bodies (LBs) and cerebrovascular pathology are related to higher global parkinsonian scores proximate-to-death. This study extended these findings by examining whether any specific vascular pathologies interact with LBs to potentiate the global parkinsonian scores and parkinsonian signs including gait impairment, bradykinesia, rigidity, and tremor. Methods: We studied brain autopsies from 1753 deceased participants (mean age-at-death=89.3 years, SD=6.74; 32% men) from the Religious Orders Study, Rush Memory and Aging Project, and the Minority Aging Research Study who underwent evaluation of parkinsonian signs with a modified version of the motor section of the Unified Parkinson's Disease Rating Scale. Autopsied brains were evaluated for LBs, macroscopic and microscopic infarcts, and the severity of arteriolosclerosis, atherosclerosis, and cerebral amyloid angiopathy (CAA). A series of regression analyses included main effect variables assessed interactions on global parkinsonism scores and parkinsonian signs, adjusted for age, sex, and education. Results: More than 30% of cases showed cerebrovascular pathologies and about 26% had LBs. The interaction between LBs and macroscopic infarcts was associated with higher global parkinsonian scores (β = 0.434, SE = 0.167, p = 0.009) and specifically parkinsonian gait (β = 0.641, SE = 0.236, p = 0.006), such that participants who had macroscopic infarcts and LBs exhibited higher global parkinsonian scores and gait impairment scores compared to participants who had only LBs or macroscopic infarcts. Results were unchanged after controlling for other vascular pathologies. By contrast, there was no interaction between LBs and other cerebrovascular pathologies for global parkinsonian or domain scores. Conclusions: These results suggest a synergistic link between LBs and macroscopic infarcts to further increase parkinsonian signs, specifically parkinsonian gait impairment in older persons, and highlight the impact of mixed vascular and neurodegenerative pathologies on the loss of motor function. 32 Characterization of Microhemorrhages in CADASIL Zesheng Chen1, Alyscia Severance2, Christopher Williams3, Chuo Fang4, Rajesh Kalaria5, Shino Magaki3, Harry Vinters3, Mark Fischer4 1UCLA Division of Neuropathology; 2UCLA David Geffen School of Medicine; 3UCLA Neuropathology; 4UCI Neurology; 5Newcastle University Neuropathology Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the most common genetic small vessel disease (SVD), is the most frequent heritable cause of stroke and vascular dementia. It results from dominant mutations in the NOTCH3 gene which lead to vessel wall thickening and medial degeneration of small arteries and arterioles, predominantly in the subcortical white matter and deep grey matter, and multiple small ischemic infarcts. Although cerebral microbleeds (CMBs) are a common finding on magnetic resonance imaging in subjects with CADASIL, they are also seen with age and other SVDs such as hypertensive arteriopathy and cerebral amyloid angiopathy, albeit with differential patterns of distribution. Furthermore, large intracerebral hemorrhages are uncommon in CADASIL, and the association of CMBs with microhemorrhages on neuropathologic examination is unclear. In this pilot study, we characterized microhemorrhages in CADASIL patients by examining autopsy brain tissue of four subjects from the genetically confirmed Newcastle CADASIL cohort. The distribution and extent of microhemorrhages were assessed on Prussian blue stain in the frontal cortex and subcortical white matter, basal ganglia and cerebellum and was correlated with lacunes and microinfarcts, vessel wall thickening and severity of vascular smooth muscle cell degeneration on immunohistochemistry for smooth muscle actin. All four cases showed multiple lacunar infarcts or microinfarcts and moderate to severe vessel wall thickening. Microhemorrhages were seen in all subjects in all areas, most pronounced in the basal ganglia around small to medium sized arterioles, and did not correlate with severity of vascular changes or presence of infarcts locally. These results demonstrate that microhemorrhages are frequent in the brains of CADASIL patients and suggest that interaction of multiple factors likely underlie the pathogenesis of microhemorrhages in CADASIL. Friday Posters   Tumors 1 33 Molecular Features Associated with Over 36- and 120-Month Survival in Three Large Cohorts of Glioblastoma Patients Timothy Richardson1, Kalil Abdulla2, Kimmo Hatanpa2, Jamie Walker1 1UT Health San Antonio; 2UT Southwestern Medical Center Glioblastoma (GBM; WHO grade IV) represents a molecularly diverse class of infiltrative astrocytomas, primarily affecting adult patients. Initially diagnosed solely on the basis of histologic characteristics, recent work has identified several defining molecular characteristics that have been incorporated into diagnostic and prognostic schemes, in many cases outperforming traditional histologic features. Despite significant treatment advances and progress in understanding the underlying biology of these tumors, the prognosis remains dire; approximately 5% of patients survive longer than 5 years after initial diagnosis, and many publications use 36 months as a guidepost for “long-term survival” (LTS) designation. Using univariate and multivariate statistical tools, we analyze the clinical and molecular features of 3 large independent cohorts (n=492, n=567, and n=246), containing 196 LTS cases and 17 cases with “very long-term survival” (VLTS; survival >120 months). In the general GBM patient population, younger age, low overall copy number variation (CNV) levels, IDH1/2 mutation, MGMT promoter methylation, and lack of CDKN2A deletion are all enriched in LTS cohorts. Within the IDH-mutant cohort, only younger patient age and lower overall CNV were associated with longer survival, although there was a non-significant trend toward MGMT promoter methylation. In the IDH-wildtype cohort, younger patient age, MGMT methylation, and lack of cIMPACT-NOW 3 factors were all significantly associated with survival >36 months. These data agree with our re-analysis of 2,328 previously published cases (LTS n=465) (Richardson et al., 2020). While there is no definitive molecular signature that guarantees long-term survival in glioblastoma patients in this dataset, these results suggest a constellation of clinical and molecular features that may help guide clinical decision making and predict which patients have the best odds of long-term survival. 34 An Integrated Tool to Predict Venous Thromboembolism in Glioma Patients Dusten Unruh1, Michael Drumm1, Jonathan Lamano1, Qazi Haider1, Jonathon Judkins1, Margaret Schwartz1, Yuping Li2, Anh Tran1, Rodrigo Javier1, Kathleen McCortney1, Christina Amidei1, Kirsten Bell-Burdett1, Denise Scholtens1, Craig Horbinski1 1Northwestern University; 2Washington University, St. Louis Background: Venous thromboembolism (VTE) is a debilitating and life-threating condition that is common in patients with cancer, especially glioma. There are no widely-accepted guidelines for antithrombotic prophylaxis in glioma patients, in part because of the risk of iatrogenic intracerebral hemorrhage. Effective VTE prediction models exist for patients with other cancers, but not glioma. Our prior publications suggested a protective role of IDH1 mutations (IDHmut) against VTE, as well as a positive association between elevated circulating Tissue Factor (TF), a procoagulant secreted by cancers, and VTE in glioma patients. Others have recently found a correlation between podoplanin, a platelet activator, and cancer-associated VTE, but this has not yet been proven in gliomas. Our objective was to develop a multidimensional VTE prediction tool to improve glioma patient care, incorporating clinical, blood-based, histologic, and molecular markers. Methods: The Northwestern University Nervous System Tumor Bank provided preoperative arterial blood, tumor tissue, and clinical-pathologic data from 254 grade II-IV glioma patients over a 4-year interval. Molecular profiling was done by GlioSeq NGS. Results: Forty-six out of 254 grade II-IV glioma patients (18%) experienced VTE during their disease course. VTE was associated with worse median overall survival (18 vs. 54 months, P<0.001). Positive risk factors for VTE included advanced patient age, high body mass index, high tumor grade, prior history of VTE, coronary artery disease, hyperlipidemia, hypertension, and elevated circulating TF activity, among other variables. While tumor expression of podoplanin positively correlated with VTE, circulating podoplanin did not. Among molecular markers, the strongest was IDHmut, being associated with greatly reduced VTE risk (OR=0.28; 95% CI=0.12-0.64, P=0.001). Conclusions: This study identified multiple risk factors for glioma-associated VTE. Using these data, we have developed a web-based multivariable integrated prediction calculator to identify glioma patients who would benefit the most from prophylactic anticoagulation. 35 The Epileptic Landscape of Diffusely Infiltrative Gliomas Michael Drumm1, Jessica Templer1, Omar Bushara1, Dusten Unruh1, Jordain Walshon1, Rodrigo Javier1, Kathleen McCortney1, Geoff Swanson1, Craig Horbinski1 1Northwestern University Seizures are among the most prevalent co-morbidities associated with diffuse glioma, and pose a serious threat to patients. Our prior work showed that IDH mutation (IDHmut) was associated with much greater seizure frequency at the time of initial glioma diagnosis. However, less is known about the variables that contribute to seizure risk throughout the course of disease. We therefore collected data from 247 patients with grade 2–4 glioma, and determined seizure risk using Kaplan-Meier survival probabilities and multivariable cox regression analyses. Median follow-up of IDH wildtype (IDHwt) and IDHmut glioma patients was 15 months and 36 months, respectively. Incidence of pre-operative seizures for IDHwt and IDHmut patients was 75/168 (45%) and 60/79 (76%), and incidence of post-operative seizures was 70/168 (42%) and 43/79 (54%), respectively. Patients who had a pre-operative seizure had a shorter time to their first post-operative seizure than patients who never had a pre-operative seizure in both IDHwt (P<0.0001) and IDHmut (P=0.039) cohorts. Among IDHmut glioma patients, those that had subtotal resections developed post-operative seizures faster (median time to first seizure=9.9 months) than those with gross-total resections (median not reached) (P=0.0005), but a similar pattern was not observed in IDHwt glioma patients (P=0.20). Patients with IDHmut astrocytomas more quickly developed post-operative seizures (median=11.1 months), compared to those with IDHwt astrocytomas (24.9 months) or IDHmut oligodendrogliomas (median not reached) (P=0.033). Tumor progression closely followed post-operative seizures in patients with IDHwt gliomas when either their first post-operative seizure occurred longer than 6 months following resection, or when their post-operative seizures worsened in quality. These data suggest the best predictors of post-operative seizures are as follows: (i) the presence of pre-operative seizures; (ii) extent of surgical resection; (iii) IDHmut status. These data will help clinicians better manage glioma patients by identifying those at greatest risk of seizures. 36 Clinical Molecular Profiling of IDH-wildtype Glioblastoma Adult Patients: Old Patterns and New Insights Cristiane Ida1, Corinne Praska1, Cinthya Zepeda Mendoza2, Thomas Kollmeyer1, Asha Nair1, Paul Decker1, Aditya Raghunathan1, Caterina Giannini1, Rachael Vaubel1, Jorge Trejo-Lopez1, Aivi Nguyen1, Mark Jentoft1, Kliment Donev1, Kevin Halling1, Gang Zheng1, Margaret DiGuardo1, Benjamin Kipp1, Robert Jenkins1 1Mayo Clinic; 2Department of Pathology, University of Utah/ARUP Laboratories Adult-type IDH-wildtype glioblastoma (IDHWT-GBM) is morphologically and molecularly heterogeneous. We describe the molecular patterns of 871 unique tumors with integrated diagnosis of IDHWT-GBM (H3.3-G34-mutant and recurrent tumors excluded) in adult patients (≥18 years) that were clinically tested (2017-2020) using a 219-gene mutation and fusion/transcript variant (n=685; 19 mutation-only) or 50-gene mutation (n=186) targeted neuro-oncology NGS panel, chromosomal microarray (n=352) and MGMT promoter (MGMTp) methylation-specific RT-PCR (n=649). SMARCAL1 was only evaluated by microarray. TERT promoter (TERTp) mutation was the most frequent abnormality and delineated 2 subsets: TERTp-mutant (TERTpMUT; n=725, 83%) and TERTp-wildtype (TERTpWT; n=146, 17%). TERTpWT tumors occurred in younger patients (mean±SD age 50±17 versus 60±13 years, p-value <0.001) and involved midline structures more often (10% versus 2.5%, p-value <0.001) than TERTpMUT tumors. By NGS, the most frequent abnormalities (>10% cases) were mutations involving PTEN>TP53>EGFR (also transcript variants)>NF1>RB1 in TERTpMUT and TP53>NF1>PTEN>EGFR (transcript variants)>RB1>ATRX>BRAF in TERTpWT tumors. EGFR and NF1 mutations only rarely co-occurred (0.5%; 4/871). TERTpMUT tumors were enriched for PTEN and EGFR mutations whereas ATRX, BRAF, FGFR1, PPM1D and PDGFRA mutations were more frequent in TERTpWT tumors (p-value <0.001 for all comparisons). Only 3 cases (0.3%) were negative for a clinically relevant mutation (1 case had a ST7-MET fusion and multiple abnormalities including PDGFRA/MET amplification and CDKN2A/B homozygous deletion; 2 cases evaluated by 50-gene mutation panel only). Preliminary copy number data analysis revealed potential alternative copy number-driven telomere maintenance mechanisms involving TERT (n=16), ATRX (n=7) and/or SMARCAL1 (n=5) in 45% (25/55; 2 TERT/SMARCAL1, 1 TERT/ATRX) of TERTpWT tumors with available data. Presence of MGMTp methylation was similar between TERTpMUT and TERTpWT groups (34% versus 29%, p-value 0.38). Clinical molecular profiling of IDHWT-GBM recapitulates and expands the spectrum of previously reported patterns, underscoring the molecular heterogeneity of IDHWT-GBM and providing a valuable dataset to unravel novel patterns and associations. 37 Cytogenetic and Molecular Correlates of Glioblastoma with Unusual Histologies Jared Ahrendsen1, Nancy Hsu1, Christine Bryke1, Hemant Varma1 1Beth Israel Deaconess Medical Center Introduction: Glioblastoma (GBM) is characterized by intra- and inter-tumor histologic variability. Several histologic variants of GBM have been described; however, the underlying cytogenetic and molecular characteristics of GBM histologic variants are poorly understood. Methods: A retrospective review was performed on every GBM case from our institution in which array comparative genomic hybridization and/or targeted next generation sequencing was performed during the years 2016-2020, yielding 71 cases. Centralized review of histologic features was performed for all cases. Clinical data were abstracted and cytogenetic/molecular data were tabulated for each case. Results: Central review of histologic features for each GBM revealed a range of morphologies. Unique histologies included tumors with multinucleated giant cells (gcGBM, n=15), prominent gemistocytes (gemGBM, n=6), spindle cells arranged in streaming fascicles (spindGBM, n=5), primitive-appearing cells with small cell morphology (scGBM, n=3) and ependymoma-like tumors with numerous perivascular pseudorosettes (ependGBM, n=1). Conventional GBM (convGBM, n=41) included cases with more characteristic histologic features or in cases in which other unique histology was present in <30% of the tumor. Compared to convGBM, gcGBM displayed widespread chromosomal haploidization and more frequent chromosomal losses, copy neutral loss of heterozygosity, and TP53 mutations. Most gcGMB lacked combination polysomy 7/monosomy 10 that was frequently observed in convGBM. gemGBM and spindGBM displayed cytogenetic profiles similar to that seen in convGBM. Interestingly, spindGBM cases harbored concurrent mutations in PTPN11, NF1, and TERT promotor, which was not seen in any other group. Finally, ependGBM had molecular features characteristic of IDH-mutant GBM. Conclusions: We demonstrate unique cytogenetic characteristics of gcGBM with widespread haploidization not seen in GBM with other morphologies. Similarly, spindGBM has a unique molecular signature that potentially suggests a correlate with this histologic subtype. Finally, molecular and cytogenetic studies can be helpful in correctly classifying tumors with unusual morphology, such as those with ependymoma-like or primitive/undifferentiated features. 38 Demographic Disparities between Glioblastoma Patients in Clinical Trial and Tumor Bank Enrollment Anthony Tuzzolo1, Phuong Deleyrolle2, Raquel Mctiernan2, Patrick Rickert3, Patricia Sacks4, Kaitlyn Melnick2, Jesse Kresak1 1University of Florida Department of Pathology; 2University of Florida Department of Neurosurgery; 3Washington University Department of Political Science; 4University of Florida College of Medicine Glioblastoma is the most common primary malignant neoplasm of the brain and prognosis remains poor. Although many patients elect to participate in clinical trials or donate tissue to tumor banks, some do not. If demographic differences exist between patients that participate in clinical trials compared to those that do not, this could lead to underrepresentation of certain populations. This study seeks to examine if there is disparity in participation with tumor banking and/or clinical trials for glioblastoma patients in the North Central Florida region. Our sample population consisted of 538 patients diagnosed with glioblastoma between 2016 to January 2021, of which 91.1% were Caucasian, 5.95% were African American, 0.56% were Asian, and 2.42% were designated as “Other Race”. These percentages do not vary considerably from expected values for our catchment area. Of these, 44.5% of Caucasian patients enrolled in clinical trials (218) compared to 25.0% of African American (8), 100% of Asian (3), and 76.9% of Other Race (10) patients. 213 patients were also approached for tumor banking, with 81.9% (177) consenting. Of those that consented, 85.9% of Caucasian patients (171 out of 199) consented compared to 15.3% of African American patients (2 out of 13). Compared to Caucasians, the odds ratios of African American patients enrolling in clinical trials and tumor banking were 0.412 (p<0.05) and 0.030 (p<0.01) respectively. No significant differences were noted for clinical trial or tumor bank enrollment with regards to sex or insurance status. In this study, race was the most significant factor determining whether or not a patient with glioblastoma agreed to enter a clinical trial or consent to tumor banking. 39 New Aspects of FGFR3:TACC3 Fusion-positive Adult GBMs: Metastases and New Fusion Partner Ahmed Gilani1, BK Kleinschmidt-DeMasters2 1University of Colorado Anschutz Medical Campus, Deptartment of Pathology; 2University of Colorado, Departments of Pathology, Neurology and Neurosurgery Background: FGFR3:TACC3 fusion-positive adult IDH-wildtype glioblastomas have been reported to show longer survival and a characteristic histological appearance of cellular monotony, arcuate vasculature and microcalcifications that suggest they may represent a distinct identifiable type of GBM. We recently showed, however, that some FGFR3:TACC3 fusion+ GBMs lack this characteristic morphology and conversely, that some adult IDH-wildtype GBMs do show the reported appearance but lack the fusion. We now report additional features of these tumors. Materials and Methods: Clinical follow up of our original cohort of 7 fusion-positive cases in addition to continued accrual of cases. Results: Additional clinical follow up since our publication revealed shortened survival in most of our patients. 5/7 patients died during the study period with survival durations of 4, 8, 13, 14 and 21 months. 2/7 patients are alive at 12 and 16 months after initial biopsy, one of which developed biopsy-proven dural metastases at 8 months and cervical lymph node metastasis 12 months post -diagnosis. This case further showed a PDZD2:TERT fusion in addition to the FGFR3:TACC3 fusion. A new case (8th in our series) with the reported typical histology has a heretofore unreported FGFR3 ex17-JAKMIP2 ex7 fusion. Conclusion: The role of FGFR3:TACC3 fusion in GBM tumor behavior is still being elucidated as more cases with this alteration are reported. Our exceptional case shows that FGFR3:TACC3 fusion+ GBMs may also be associated with early dissemination and extracranial metastatic spread which is rare in standard GBM. The role, if any, of the additional PDZD2:TERT fusion in metastatic spread is unknown but given the short interval of metastatic spread after diagnosis, longer survival is not responsible. The newly identified fusion+ case suggests that FGFR3 fusion-positive or FGFR3-altered might be superior terminology for this adult GBM type. 40 EWS RNA-Binding Protein 1 (EWSR1) Gene Fusions in Central Nervous System Tumors Samantha Ritacco1, Brennan Decker1, Matthew Hiemenz1, J. Keith Killian1, Shakti Ramkissoon1, Mirna Lechpammer1 1Foundation Medicine, Inc. EWS RNA-binding protein 1 (EWSR1) fusions and rearrangements, along with other alterations, have been reported in a variety of predominantly mesenchymal tumors. Several recent reports have described cases of primary “intracranial extra-axial myxoid mesenchymal tumors” and “angiomatoid fibrous histiocytoma (AFH)” harboring EWSR1 fusions. Here we report, a case series of primary CNS tumors of non-mesenchymal origin with EWSR1 fusions and rearrangements. In this study, we performed a retrospective analysis of the Foundation Medicine comprehensive genomic profiling (CGP) database including approximately 400,000 samples that were sequenced in the course of clinical care. CGP was performed using large DNA or DNA/RNA panels utilizing hybrid-capture based next-generation sequencing assays (FoundationOne, FoundationOneCDx, FoundationOneHeme). Out of 1,277 tumors found to harbor EWSR1 fusions and rearrangements, 15 (1.17%) were identified as primary intracranial CNS tumors. Seven patients were female and 8 were male (age range 2 – 67 years). Four patients were pediatric at the time of diagnosis (2, 9, 12 and 13 years). Among the primary CNS tumors identified to have EWSR1 fusions, 5 were diffuse astrocytoma, 5 were classified as primitive neuroectodermal tumors (PNET) / embryonal tumors, 2 were meningiomas and one of each were: neurocytoma, pleomorphic xanthoastrocytoma (PXA) and ependymoma. The majority of identified EWSR1 fusions were with FLI1 (n=4) and PATZ1 (n=4) genes, while the other fusion partners included ATF1 (n=2), BEND2, CREB1, PLAGL1, NF2 and ZNRF3. All tumors were microsatellite stable (MSS) and tumor mutational burden was predominantly low. Our findings indicate that primary CNS tumors of non-mesenchymal origin may occasionally harbor EWSR1 fusions. With broader application of CGP in the routine neuropathology practice, more of such cases will be identified. This in turn may lead to better understanding of the biomarker signature and clinical features of these neoplasms, and ultimately support genomic classification of intracranial tumors. 41 Cell Origin Of Central Neurocytoma: Immunohistochemical Study Using Thyroid Transcription Factor-1 (TTF-1) Hyunhee Kim1, Sung-Hye Park1, Kayoung Lim1, Jin Woo Park1, Jeongwan Kang1, Jae Kyung Won1 1Department of Pathology, Seoul National University Hospital, Seoul, Korea Background: Central neurocytoma (CN) is a low-grade neuronal tumor often located in the lateral ventricles (LV). In this study, we investigated the expression of several immunomarkers in supratentorial periventricular tumors to know the cell of origin of CNs. Methods: The specimens studied include CN (22), ependymoma (6), pilocytic astrocytoma (5), SEGA (5), subependymoma (5), pituicytoma (2), normal brain (2), and fetal brain (1) obtained from SNUH pathology archives from 2000 to 2020. We investigated the expression of several immunomarkers, including TTF-1, GLUT-1, L1CAM, SSTR2, TMHH3, Olig2, synaptophysin, and NeuN. Results: All 22 cases of CNs arose from the LV (Right: 9, left: 7, bilateral: 5, posterior horn: 1), 3 of which extended to the 3rd ventricle (13.6%). Immunohistochemically, CN showed robust positivity for synaptophysin (100%), GLUT-1 (100%, including focal positivity in 1 case), NeuN (95%), SSTR2 (95%, including focal positivity in 3 cases), TTF-1 (82%), and L1CAM (77%, including focal positivity in 27% of cases); however, they were negative for Olig2 (100%) and TMHH3 (86%). TTF-1 was also positive in SEGAs of LV (100%), pituicytomas of neurohypophysis (100%), and subependymoma of LV (20%). TTF-1 negative CNs (14%, n=3) were located outside the body of the LV, i.e., the anterior horn (n=2) and the posterior horn (n=1). In the fetal brain, TTF-1 was significantly positive in the medial ganglionic eminence, near the foramen of Monro. Conclusions: TTF-1 was positive in the fetal medial ganglionic eminence and can be positive in CN, SEGA, and subependymoma of the LV, close to the foramen Monro. This study strongly suggests that the tumor cell origin of TTF-1 positive CNs is the primitive neuronal cells of the medial ganglionic eminence. New findings in this study also include GLUT-1, SSTR2, and L1CAM positivity, and TMHH3 negativity in CNs, which has not been previously reported. 42 Primary Vertebral Ewing Sarcoma with Predominant Spindle Cell Morphology: An Uncommon Histologic Variant in a Rare Location Ashley Holloman1, Guillermo Aldave Orzaiz2, M Fatih Okcu2, Hatel Moonat2, Ronald Rauch2, Dolores Lopez-Terrada2, Carrie Mohila2 1Houston Methodist Hospital; 2Texas Children's Hospital and Baylor College of Medicine Ewing sarcoma (ES) is a high grade malignant neoplasm of bone and soft tissues and most commonly occurs in children and young adults. Primary vertebral ES involving the non-sacral spine are quite rare. Histologically, classic ES is composed of sheets of poorly differentiated small round blue cells. Atypical ES have non-classic morphology and may rarely show spindle cell features. The spindle cell component usually only comprises a minor component of an otherwise classic ES. We present a 13-year-old boy who presented with a four month history of intermittent back pain with leg weakness and numbness. Spine MRI revealed L2 vertebral body mass with extension into the paravertebral soft tissues and into the epidural space of the spinal canal displacing and severely compressing the thecal sac. Because of worsening lower extremity weakness and urinary retention, emergent decompression of the epidural component was performed. Histologically, the tumor was a high grade spindle neoplasm with foci of necrosis and increased mitotic activity. A minor population of the tumor was composed of small round blue cells. Immunohistochemistry revealed tumor cells were negative for myogenin, myoD1, desmin, S100, SOX10, BCL2, pancytokeratin, and EMA, and were strongly immunoreactive for NKX2.2 and CD99. Fluorescence in situ hybridization (FISH) identified t(11;22)(q24;q12) with resulting EWSR1-FLI1 fusion confirming the diagnosis of ES. This case highlights the importance of including ES in the differential diagnosis of a high grade spindle cell neoplasm of the vertebra particularly in the pediatric age group. This case further emphasizes the importance of integration of morphologic, immunohistochemical, and molecular features for accurate diagnosis. 43 Cerebellar Pilocytic Astrocytoma with a Sacral Drop Metastasis in an Adult Xi Wang1, Marcus Stephens1, Noojan Kazemi1, John Day1, Maher Albitar2, Murat Gokden1 1University of Arkansas for Medical Sciences; 2Genomic Testing Cooperative Introduction: Pilocytic astrocytoma (PA) is a WHO Grade I neoplasm frequently seen in the pediatric age group and commonly in the posterior fossa. Leptomeningeal spread rarely occurs in PA, mostly in pediatric patients. Spinal spread of PA in adults is extremely rare. Here, we present a case of an adult patient who initially presented with back pain and was found to have a concomitant cerebellar and sacral spinal cord PA. Case: An otherwise-healthy 20-year-old woman had a two-year history of back pain and occasional headaches. Spinal MRI revealed a homogenously-enhancing, well-circumscribed 22.6-millimeter intradural S2 mass. Brain MRI, obtained due to location and metastatic appearance of the sacral lesion, showed a homogenously-enhancing mass arising from the vermis cerebelli and occupying the fourth ventricle with ventriculomegaly. The clinical/radiological differential diagnosis included mainly medulloblastoma and ependymoma with drop metastasis, or two independent coincidental neoplasms. Microscopic examination showed a PA with biphasic histology, myxoid and dense glial areas, cytologically bland cells with round-to-oval nuclei, and Rosenthal fibers. Subsequently-resected sacral mass also showed a PA with similar histology. Immunohistochemically, BRAF V600E was negative for the mutant protein. KIAA1549-BRAF fusion was identified by FISH, and fusion protein RNA was identified by next generation sequencing in both neoplasms. A mutation in WDFY3 was also identified in the spinal lesion. Gross total resection was accomplished for both. Three years post-operatively, no recurrences, new lesions, or neurological deficits are present without additional treatment. Conclusion: PA with spinal drop metastasis is rare in adults. Although histologic features were diagnostic, identification of KIAA1549-BRAF fusion in both neoplasms further supports this diagnosis and potentially creates opportunities for targeted treatments, if needed, or in cases not amenable to adequate resection. WDFY3 is associated with autophagy, has been studied in breast and ovarian cancers, but has not been reported in gliomas to our knowledge. 44 Alterations of RECQL4 and Related Helicases in Glial Neoplasms Sarra Belakhoua1, Ming Yuan2, Charles Eberhart2, Liam Chen3, Fausto Rodriguez2 1Faculty of Medicine of Tunis; 2Johns Hopkins University School of Medicine; 3University of Minnesota Background: RECQL4 is a ubiquitously expressed protein that belongs to the RecQ Helicase family. RECQL4 plays a role in maintaining the integrity of the genome and regulating DNA replication. Our prior work reported gene variants of RECQL4 in NF1-associated tumors, sometimes in association with abnormal telomeres. However, the relevance of gene variants in gliomas at large is unclear. Design: Publicly available databases of genetic data were analyzed for alterations in RECQL4 and other related helicases (WRN, BLM). Immunohistochemistry using the anti-RECQL4 antibody was performed on whole tissue sections and tissue microarrays from gliomas. Normal brain tissue was used as controls. Immunoreactivity was recorded and compared with available demographic and genetic data. The H score was used to characterize tissue microarrays. Results: Analysis of the cBIOPORTAL© database of gliomas (TCGA, Cell 2016) demonstrated RECQL4 mutations in 8/794, BLM mutations in 5/794, and WRN mutations in 2/794. 35 gliomas were identified with RECQL4 gene variants by next-generation sequencing at our institution. 7 of these gene variants were possibly pathogenic/somatic. IHC studies of whole tissue sections showed consistent nuclear staining of neurons, a small subset of subcortical glial cells, and glioblastomas. The expression was partially lost in an anaplastic astrocytoma with combined RECQL4 p.L924fs and NF1 mutations. Next, 208 glial tumors of various types and grades were studied using tissue microarrays. The H score (% of cells positive x intensity) was determined for each tumor. The median H score was 120 for grades I and II, 180 for grade III, and 160 for grade IV. Conclusion: Genetic alterations in RECQL4 and related helicases occur in a subset of glial neoplasms. RECQL4 protein expression may be increased in high-grade gliomas and decreased in low-grade gliomas. The significance of these alterations requires further studies. 45 Diffuse Leptomeningeal Histiocytic Sarcoma: Histopathologic and Molecular Findings In An Autopsy Case Chinelo Onyenekwu1, Ashley Cunningham1, Kala Schilter1, Honey Reddi1, Elizabeth Cochran1 1Department of Pathology, Medical College of Wisconsin Primary central nervous system histiocytic sarcoma (HS) with diffuse leptomeningeal involvement and absence of a mass lesion is extremely uncommon. It poses a diagnostic and therapeutic challenge due to its mimicry of other disease entities and the unresectable nature of the lesion. A 42-year-old female with headache, visual changes, and concern for meningitis was admitted for encephalopathy with negative infectious and rheumatologic workup. Magnetic resonance imaging demonstrated leptomeningeal and cranial nerve enhancement with thickening. Biopsy of the trigeminal nerve showed atypical histiocytosis with a negative BRAF V600E (c.1799C>A) mutation analysis. The patient received steroid therapy, as well as treatment for meningitis and presumed Erdheim-Chester disease, with no improvement. She was eventually placed on comfort care and died 90 days after her first presentation. At autopsy, there was thickening of the leptomeninges over the inferior frontal lobes, ventral pons, medulla, and spinal cord with enlarged ventricles. The cranial nerves were thickened, and spinal roots matted together. Histologic examination demonstrated extensive histiocytic proliferation involving the leptomeninges over the cerebrum, brainstem, cerebellum, spinal cord, and extending into the ventricular system. The histiocytic proliferation infiltrated between the axons of the cranial and spinal nerves and displayed variable degrees of atypia with irregular nuclear contour, stippled chromatin, occasional visible nucleoli, and mitotic figures. Frequently, the tumor cells showed preferential perivascular localization. The tumor cells were strongly positive for CD163 and negative for CD1a, CD45 and S100. There was no evidence of an associated lymphoma. Next-generation sequencing revealed variants involving ARID1A, CDKN2A, and SETD2, which have been previously identified in patients with HS; additionally, variants involving BRIP1 and POLE were also identified. Disseminated leptomeningeal HS, although a rare malignant neoplasm with a dire outcome, should be considered in addition to more common disease entities such as meningitis or autoimmune encephalopathy, especially in patients unresponsive to therapy. 46 Molecular Characterization of the Malignant Transformation of a Suprasellar Teratoma Heather Maioli1, Vera Paulson2, Sananthan Sivakanthan3, Ariana Barkley3, Luis Gonzalez-Cuyar1, Manuel Ferreira3, Caitlin Latimer1 1University of Washington, Division of Neuropathology; 2University of Washington, Genetics Division; 3University of Washington, Neurological Surgery Sellar and suprasellar teratomas are rare, comprising approximately 0.5% of all intracranial tumors. These tumors are most frequently encountered during the first two decades of life and have a slight predilection for males. While mature teratomas have a good prognosis with low recurrence rates and a 90-100% 10-year survival with surgical resection and radiotherapy alone, malignant transformation has rarely been reported. We describe a case of a 43-year-old man who initially presented at age 16 with a suprasellar teratoma and who, after multiple resections and radiation therapy, re-presented more than two decades later with vision complaints, headaches, and right facial numbness. MRI showed a heterogeneously enhancing suprasellar mass for which he underwent resection. Examination of the resection specimen revealed adenocarcinoma, the origin of which was uncertain given the rarity of malignant transformation of mature teratoma in the central nervous system. To determine the origin of the adenocarcinoma, a comparison of the 2020 resection with the patient’s initial 1993 resection was undertaken, including both histologic review and molecular profiling using targeted DNA sequencing. The teratoma at initial presentation had histologically similar elements to the recently resected adenocarcinoma, including a prominent mucinous epithelial component, but lacking the complex architecture, cytologic atypia, and mitotic activity. Both neoplasms shared an activating KIT deletion (p.Asn566_Asp572del) and copy gain of chromosome 12p, while the 2020 resection specimen also demonstrated additional copy alterations including FGFR3, CCND1, and MDM2 amplification. Together, the histologic and molecular characteristics support malignant transformation of the mature teratoma. To our knowledge, this represents the first report documenting molecular alterations of a suprasellar teratoma and subsequent malignant transformation. This case also brings attention to the rare, but serious complication of malignant transformation in intracranial teratomas, sometimes occurring decades later, perhaps arguing for longer follow up in some patients based on the molecular signature. 47 Spinal Calcifying Pseudoneoplasm of the Neuraxis (CAPNON) Overlapping and Linking with Calcified Synovial Cysts Jian-Qiang Lu1, Waleed Mohammadi1, Crystal Fong1, Kaiyun Yang2, John Provias1, Snezana Popovic1, Ivan Chebib3, Aleksa Cenic1 1McMaster University; 2University of Toronto; 3Massachusetts General Hospital, Harvard Medical School Calcifying pseudoneoplasm of the neuraxis (CAPNON) is a rare tumor-like fibro-osseous lesion in the neuraxis including the spine. It is diagnosed typically by the presence of the following histopathological features: granular amorphous to chondromyxoid fibrillary cores with calcification/ossification, peripheral palisading of spindle to epithelioid cells, variable fibrous stroma, and foreign-body reaction with multinucleated giant cells, as well as positive NF-L immunostaining in lesion cores. Spinal CAPNON is sometimes classified as tumoral calcinosis that is tumor-like dystrophic calcification usually in the periarticular tissue and also described in calcified synovial cysts (CSCs) or degenerated ligamentum flavum with pseudocystic formation. Our present study aims to examine the similarity and difference, as well as possible link between CAPNON and CSC. We reviewed pathological, radiological and clinical features of 5 spinal CAPNONs and 21 spinal CSCs including 3 recurrent lesions. All CAPNONs exhibited diagnostic histopathological features and prominent NF-L positivity. In contrast, CSCs showed synovial cell lining and variable degenerative changes with granular amorphous areas, calcification/ossification, surrounding spindle to epithelioid cells, and histiocytes including occasional multinucleated giant cells, but no to minimal NF-L positivity except four lesions. These four lesions were clinically and pathologically diagnosed as CSC, but also diagnostic of CAPNON with prominent NF-L positivity and the infiltration of more CD68-positive histiocytes and variable CD8-positive T-cells; one of these lesions was recurrent with more prominent features of CAPNON compared to the primary lesion, possibly in transition from CSC to CAPNON. While the pathogenesis of CAPNON remains elusive but likely reactive/degenerative in association with an inflammatory/immunological process involving NF-L protein deposition, our findings suggest that CAPNON may arise from a degenerated synovial cyst with increasing calcification and other reactive changes. There are radiological and histopathological overlaps between CAPNON and CSC lesions, but NF-L immunostaining is a useful marker to distinguish from CAPNON from CSC. 48 Disappearance of DNA Mismatch Repair-deficient Sub-clones in a High Grade Glioma after Immune Checkpoint Inhibitor Therapy Rimas Lukas1, Christina Amidei1, Nathan Demars2, Arnold Gelb3, Jill Buck2, Sean Sachdev1, Alexander Feldman1, Matthew Tate1, Karan Dixit1, Daniel Brat1, Lawrence Jennings1, Craig Horbinski1, Matthew McCord1 1Northwestern University, The Feinberg School of Medicine; 2Ziopharm Oncology; 3Bristol-Myers Squibb High-grade gliomas remain an unmet medical need. Immune checkpoint inhibitors have shown promise in fighting other types of cancer through stimulating the immune system, but results with gliomas have been inconsistent. Recently, the Controlled IL-12 gene therapy system has shown promise in increasing glioma immunogenicity. This system stimulates IL-12 production through a locally administered adenoviral vector, which delivers genetic information for IL-12 and a transcription switch. An oral activator ligand, veledimex (VDX), controls transcription levels. IL-12 activity leads to production of IFN-gamma, increasing tumor immunogenicity. A recent phase 1 clinical trial showed that Controlled IL-12 can increase expression of PD-1 and PD-L1 in tumor-associated T-cells. This supports investigating Controlled IL-12 in combination with immune checkpoint inhibitors. We describe a patient with a recurrent grade 4 IDH mutant astrocytoma which developed subclones of inactivating DNA mismatch repair (MMR) gene alterations after temozolomide (TMZ) therapy. The patient received Controlled IL-12 plus PD-1 blockade and responded well. Several months later, the tumor recurred again and was re-resected. Analysis showed that the inactivating DNA MMR gene alterations had disappeared. Furthermore, the tumor showed granulomatous inflammation, abundant T cells, eosinophils, and plasma cells. Over one year later, the patient succumbed to the tumor. Post-mortem analysis revealed that DNA MMR alterations were still gone; the previously observed inflammatory infiltrates were also gone. These data suggest that TMZ-driven DNA MMR inactivation is a sub-clonal process, and that MMR-deficient tumor sub-clones are preferentially targeted through immunotherapy. 49 Myeloid Sarcoma Involving the Central Nervous System Matthew Vega1, Natalia Lashmanova1, Paolo Gattuso1, Xinhai Zhang1 1Rush University Medical Center Introduction: Myeloid Sarcoma is a rare pathologic entity, most often seen in patients with pre-existing myeloid disorders. Published medical literature on myeloid sarcoma involving the central nervous system in adults is sparse and mainly confined to single case reports. We report the clinical/pathological findings of a series of adult patients with central nervous system involvement by myeloid sarcoma. Materials and Methods: The surgical pathology files between 1992 and 2019 were searched for myeloid sarcoma and central nervous system. The clinical and pathologic data were reviewed in detail. Results: Between 1992 and 2019 a total of 55 myeloid sarcomas were recorded with 11/55 (20%) involving the brain. There were seven males and four females, with an age range between 43 to 82, mean age 61 years. Five cases were subdural, four cases were epidural and two cases were intraparenchymal lesions (frontal and posterior fossa). 3/11 cases (27.7%) had concomitant CSF examination. The most common clinical presentation of brain involvement by myeloid sarcoma is subdural bleeding 5/11 (45.5%). 6/11 cases (24.7%) of the brain were the primary manifestation of the disease. Concomitant bone marrow biopsy was performed in 7/11 (63.7%) cases, 6 cases were positive for AML and 1 case was negative. The interval time between the primary diagnosis and central nervous involvement was between 3 to 36 months with an average time of 17 months survival. Conclusion: Myeloid sarcoma involving the central nervous system is rarely seen in clinical practice. It is not unusual to have brain involvement as a primary clinical presentation of myeloid sarcoma 6/11 (54.5%). Thus, heightened attention to CNS involvement by myeloid sarcoma should be incorporated into the differential diagnosis of CNS lesions, especially when evaluating subdural bleeding. 50 Characteristics of Adult Diffuse Midline Gliomas, Including a Case with False Negative H3K27M Immunohistochemistry Farah El-Sharkawy1, Allan Wang1, Rachel Kolster1, Richard Phillips1, H Isaac Chen1, Stephen Bagley1, Jason Rosenbaum1, MacLean Nasrallah1 1University of Pennsylvania Since 2016, our institution has diagnosed more than 20 adults with diffuse midline gliomas (DMG) with the H3K27M mutation (HGVS nomenclature: H3F3A p.K28M). The patients’ ages range from 20 to 75 years, with a median of 32 years; male patients outnumber female patients. To date, 8 patients are alive, 14 patients are deceased, and 1 patient is lost to follow up, with a median overall survival of 10 months (range 0.9 to 40.5 months). In addition to the defining H3F3A p.K27M variant, many additional variants were detected in the neoplasms, with variants in NF1, BRAF, ATRX, TERT promoter, TP53 and FGFR1 occurring in multiple tumors. Complete imaging and molecular details as well as survival data are presented. We highlight the case of a 38-year-old female who presented with several weeks of dizziness followed by an acute worsening of mental status. Brain MRI showed a heterogeneous hemorrhagic mass in the left para-midline cerebellum, vermis and pons, measuring 4.8 x 4.2 x 3.8 cm, and obstructing the fourth ventricle. The patient underwent a suboccipital craniotomy for tumor resection, and H&E stained sections demonstrated a cellular infiltrating glial tumor with severe nuclear pleomorphism, focal pseudopalisading necrosis, and microvascular proliferation. The immunohistochemical stain for H3K27M was negative multiple times; however, targeted massively parallel sequencing identified the missense variant in H3F3A at codon 27 converting lysine to methionine (H3F3A p.K27M), as well as a variant of uncertain significance (VUS) in H3F3A (p.K23E), in close proximity and in cis with p.K27. We hypothesize that the VUS interfered with antibody binding, leading to the false negative result on immunohistochemistry. To our knowledge, this is the first reported false negative using H3K27M IHC, a very robust immunomarker essentially 100% sensitive and specific according to multiple reports. 51 Neurotropic Influenza A Virus as an Oncolytic Virotherapy for Glioblastoma and Melanoma Joshua Klonoski1, NIco Contreras1, Jeremy Snook1, Cheryl Palmer1, Christian Davidson1, Matthew VanBrocklin2, Matthew Williams1 1University of Utah; 2Huntsman Cancer Institute After more than two decades of clinical trials and the first FDA approved oncolytic virotherapy, much work remains to realize the potential of using modified viruses to target solid tumors. Recent work with low pathogenicity avian influenza, modified common laboratory strains and seasonal isolates have demonstrated promise for using the influenza A virus to target solid tumors. Herein we used the Wilson Smith Neurotropic virus (A/WSN/33 – H1N1) to examine replication in an immortalized mouse astrocyte (MC41cre), human glioblastoma (SNB19, SNB75, LN229, U251, U373 and SF295) and melanoma (C8161, C32, CHL-1 and A375) as well as congenic mouse melanoma (Yumm 1.1, 1.7D5, 2.1 and 3.2) cell lines. Lytic viral infections were observed in all cell lines except for U373 and Yumm 5.2. Direct comparison of relative oncolytic potential was then performed using common laboratory and recent vaccine strains of influenza. WSN showed significantly enhanced replication compared to common laboratory and vaccine strains in the MC41cre, SNB19, SNB75, LN229, U373, CHL-1, C8161 and Yumm 1.1 cell lines with median tissue culture infectious doses of 3.5, 4.1, 3.6, 4.0, 3.6, 5.6, 3.9 and 4.8 (log/mL), respectively. Importantly, WSN possessed significantly improved replication over A/PR8/34, a contemporary isolate and one of the most common laboratory strains with demonstrated oncolytic potential. WSN also shows significant replication compared to seasonal strains in the Yummer 1.7D5, 2.1 and 3.2 cell lines. Overall, this work suggests that the neurotropic influenza A virus has unique potential as an oncolytic virotherapy and provides rationale for comparative studies in mouse models of melanoma and glioblastoma. 52 High Expression of TACC3 is Associated with a Poor Prognosis in Primary Central Nervous System Lymphomas Yasuo Sugita1, Kotaro Matsuda2, Takuya Furuta2, Koichi Ohshima2, Kenji Takahashi3, Koichi Higaki4, Akiyoshi Kakita5 1Department of Neuropathology, Neurology Center, St. Mary's Hospital; 2Department of Pathology, Kurume University School of Medicine; 3Department of Neurosurgery, Neurology Center, St. Mary’s Hospital; 4Department of Pathology, St. Mary’s Hospital; 5Department of Pathology, Brain Research Institute, Niigata University Transforming acidic coiled-coil containing protein 3 (TACC3) is essential for microtubule growth and stability when localizing to the centrosome during mitosis. Microtubule fusion is necessary for the formation of the mitotic spindles, that segregate chromosomes. Abnormality of microtubules/centrosomes causes mitotic spindle defects and associated with the tumorigenesis of various cancers. The role of TACC3 in primary central nervous system lymphomas (PCNSLs), however, remains unknown. To clarify the exact role of TACC3 in PCNSLs, the present study assessed the expression of TACC3, p53, Ki-67 in 43 PCNSLs, using immunostaining, and the statistical prognostic study of the patients. The expression level of TACC3 was assessed as the proportion of immunostaining cells to the total number of cells from three randomly selected HPF (high power fields). Cytoplasmic staining of TACC3 was evaluated as follows: 0-30% positive cells; low, 30-60% positive cells; moderate, >60% positive cells; high. Regarding p53, Ki67 staining, the average counts from the three areas were recorded as the number of nuclear staining from randomly selected HPF. TACC3 expression was detected in 37 of 43 DLBCLs, of which 12, 10, and 15 were evaluated as high, moderate, and low, respectively. Kaplan-Meier survival curves revealed that high TACC3 expressions groups are associated with lower overall survival and worse patient prognoses compared with moderate and low expression groups (log-rank test, p<0.05). Multivariate analysis indicated that TACC3 expression was an independent prognostic factor for PCNSLs patients (Cox regression analysis, p<0.05, odds ratio=2.374). In addition, compared with the correlation between the expression of TACC3, p53, and Ki67 in tumor cells, respectively, there were positive correlations for TACC3, p53, and Ki67, respectively (Fisher’s exact test, P<0.05). These results indicated that TACC3 protein expression in PCNSLs is beneficial for predicting prognosis for patients and may be a novel therapeutic target for PCNSLs 53 Congenital Rhabdoid Tumor of the Orbit: A Case Report Anat Stemmer-Rachamimov1, Melanie Lang-Orsini1 1Massachusetts General Hospital Rhabdoid tumors are rare highly aggressive childhood tumors that most commonly involve the kidney, and the Central Nervous System (CNS). We report the case of a newborn girl, born at 38 weeks gestation, which at birth was noted to have a large orbital mass. Prenatal ultrasounds at 20 weeks and 33 weeks were normal, but the head was not visualized in the latter. Magnetic Resonance Imaging (MRI) revealed an extensive left orbital and intracranial neoplasm, extending into the cavernous sinus with compression of the internal carotid arteries bilaterally. This resulted in extensive bihemispheric ischemic injury to the brain. The baby died 5 days after birth and an autopsy was performed. Gross examination revealed marked proptosis of the left eye which protruded from the face (6.8cm diameter), with the cornea recognizable on the surface. The mass extended into the cranium, involving the left middle cranial fossa, compressing the left temporal lobe and displacing the left hemisphere to the right. Examination of the body showed innumerable tan-white metastatic nodules in the lungs, liver, heart, pancreas, adrenals, right kidney and soft tissues. Microscopic examination revealed a densely cellular tumor composed of sheets of primitive round cells with scant cytoplasm. Mitotic figures were numerous and there were large areas of necrosis. The tumor was mostly behind and around the globe, and invaded the skull and, focally, the brain. Immunohistochemical staining showed rare GFAP-positive cells, and complete loss of nuclear INI1. Next-generation sequencing revealed a deletion of SMARCB1, confirming the diagnosis of rhabdoid tumor. Mutation analysis of normal tissue showed no germline mutation. While the site of origin cannot be determined definitively, the highest tumor burden was in the orbit, making this the most likely primary site. Congenital orbital rhabdoid tumor is rare and only a few cases are reported in the literature. 54 Secondary Parenchymal CNS Involvement by Lymphoma Including Rare Types: Follicular and EBV+ NK/T Cell Lymphoma, Nasal Type BK Kleinschmidt-DeMasters1, Ahmed Gilani1 1University of Colorado Anschutz Medical Campus Background: Secondary CNS involvement by lymphomas is uncommon, but when it occurs, is usually due to diffuse large B cell lymphoma (DLBCL). Many examples generate leptomeningeal or dural spread, not multifocal parenchymal tumor deposits, yet over the period of 5 weeks, we have encountered 3 such cases. Objective: To report CNS parenchymal involvement by DLBCL, relapsed/refractory stage IV extranodalnatural killer/T-cell lymphoma, nasal type (ENKL), and follicular lymphoma with high-grade transformation. Cases: The DLBCL occurred at 7-year interval from primary in a 54-year-old woman who presented with ocular and stroke-like symptoms; a massive right postcentral gyrus 2.6 x 2.9 x 2.6 cm mass was seen. The ENKL occurred at 25-month interval from nasal biopsy in an HIV-negative Caucasian 45-year-old man with 1 week of altered mental status, slowed processing of information and memory issues and multifocal cerebral and brainstem lesions were identified. The follicular lymphoma occurred at 6-month interval in a 69-year-old woman with 1 month of diplopia and 2 weeks of cognitive decline; multifocal lesions involved temporal lobe, subependymal periventricular areas, brainstem, cerebellum, hypothalamus, corpus callosum and left gyrus rectus. Conclusion: DLBCL CNS relapse occurs in 5-25% of cases, still sufficiently uncommon that many neuropathologists do not encounter such cases. EKNL, nasal type, is an aggressive, locally destructive lymphoma most often occurring in Asian countries or persons of Asian heritage and even then, seldom involves the CNS (<6% of cases), either by direct extension or secondary spread. Follicular lymphoma seldom results in CNS relapse (Ann Hematol 2020; 99:1823-1831) but when it does, is often leptomeningeal or dural, and manifests high-grade transformation as we have previously reported (Surg Neurol. 2006; 65:590-594). All 3 cases generated preoperative diagnostic difficulties, prompted consideration of infections, and all 3 remain instructive for neuropathologists. 55 The Immune-genetics Profiling of the CNS Metastatic Cancers Compared to their Primary Tumors Malak Abedalthagafi7, Sally Al Abdulmohsen1, Lamees Alhabeeb1, Duna Barakeh2, Shahd Almohsen3, Doaa Alayed2, Sara AlAnazi4, Malak AlZahrani2, Ebtehal Alsolme1, Fatimah Alqubaishi5, Amal Almutairi5, Albandari Binowayn5, Sarah AlOtaibi5, Fahad Alkhureeb1, Wafa Al Shakweer1, Hindi Al-Hindi6, Ali Alassiri3 1King Fahad Medical City; 2King Saud University Medical City; 3King Abdulaziz Medical City, Ministry of National Guard; 4Security Forces Hospital; 5King Abdulaziz City for Science & Technology; 6King Faisal Specialist Hospital & Research Centre; 7King Fahad Medical City and King Abdulaziz City for Science & Technology The most common central nervous tumors are metastatic tumors . Over half of the patients die within a few months following the diagnosis of brain metastasis. The management of brain metastases remains a challenge, with radiation therapy playing a vital role in the treatment strategy while surgery and systemic chemotherapy are reserved for failed treatment or palliative care . Characterization of actionable genomic alteration in the brain metastasis would be a more sensible clinical approach for selecting targeted therapy. We performed the Oncomine Comprehensive v3 Assay using the Saudi Human Genome platform on a cohort of 72 patients with matched brain metastases and primary tumor archival paraffin-embedded tissue blocks. Moreover, immunohistochemical studies of PDL1 were done on tissue sections to identify differences between the primary tumor and the brain metastasis. The results have shown an increase in the number of variants of each mutated gene in primary mammary invasive ductal tumors which have significantly decreased in their brain metastatsis counterparts. The genes involved were BRCA1, BRCA2 and RB1. On the other hand, samples of renal cell carcinoma have shown more mutations and more genes involved in brain metastatic samples in comparison to primary tumors. The genes involved were RET, FANCI, NOTCH2, NFE2L2, PIK3CB, RAD50, RET, PTCH1, PTEN, ATM, CHEK1, CDKN1b, FANCA, TP53, CDK12, NOTCH3 and BTK . Metastatic colorectal adenocarcinoma samples have also showed an increase in the number of genes involved along with their variants including NOTCH2, XPO1, SETD2, ATR, FGFR, EGFR, PTCH1, HRAS, BRCA2, NF1, SMARCA4 among others. Our results show distinct differences in genomic profile between the primary tumor and the brain metastasis. Identifying the mutation signatures of brain metastases is therefore necessary for selecting targeted therapy, and this change in clinical management may radically improve the prognosis. 56 Investigating the Use of p16 Immunohistochemistry as a Surrogate Marker for CDKN2A/B Homozygous Deletion in Astrocytomas Benjamin Cho1, Melissa Umphlett1, Nadejda Tsankova1 1Mount Sinai Hospital Introduction: cIMPACT-NOW has recommended that homozygous deletion of CDKN2A/B be a criterion for designating IDH-mutant astrocytomas as WHO grade 4. Prior studies have examined the relationship between p16 immunohistochemistry (IHC) and CDKN2A/B loss, but conclusions have been mixed. In this study, we explore whether semi-quantitative evaluation of p16 IHC could eliminate the need for CDKN2A/B molecular testing in astrocytomas. Methods: From the WHO grade 2-4 astrocytomas diagnosed at our institutions since 2019, 59 unique patient cases were evaluated for p16 expression by IHC, scoring positive nuclear staining as percentage of cells in tumor-rich areas (<1%, 1-10%, 11-20%, etc. up to 91-100%). In 31 of the 59 cases, CDKN2A/B homozygous deletion status was determined by next-generation sequencing (30 cases) or FISH (1 case). Results: The cases with molecular correlation included 21 IDH-wildtype glioblastomas (GBMs); 4 IDH-mutant GBMs; 4 IDH-mutant anaplastic astrocytomas (AAs); 1 IDH-wildtype diffuse astrocytoma (DA); and 1 IDH-mutant DA (19 males, 12 females; 25-76 years of age; 30 supratentorial, 1 spinal cord DA). In all 19 cases with homozygous deletion of CDKN2A/B, p16 expression was 20% or less (8 with <1%; 10 with 1-10%; 1 with 11-20%). In all 9 cases with p16 expression of 21% or greater, CDKN2A/B homozygous deletion was not detected. There were 3 cases with p16 expression of 20% or less in which no homozygous CDKN2A/B deletion was identified: an IDH-wildtype GBM (p16 1-10%); an IDH-mutant AA (p16 11-20%); and the spinal cord IDH-wildtype DA (p16 <1%). Conclusions: In this series of 31 cases, CDNK2A/B homozygous deletion was not found when greater than 20% of cells in tumor-rich areas expressed p16 by IHC. This finding raises the possibility of a threshold of p16 expression beyond which molecular testing for homozygous CDKN2A/B deletion could be reasonably forgone. Additional studies are necessary to precisely define this threshold. 57 IDH-mutant Astrocytoma with EGFR Amplification – Case Series with Review of Literature Melissa Umphlett1, Khawaja Bilal2, Abigail Suwala3, Benjamin Cho4, Sadhna Ahuja4, Omid Rashidopour4, Michael Martini5, Mary Fowkes4, Peter Morgenstern6, Matija Snuderl7, Nadejda Tsankova4 1Department of Pathology, The Mount Sinai Health System; 2Department of Pathology, Mount Sinai West; 3Institute of Pathology, Heidelberg University Hospital, Heidelberg, Germany; 4Department of Pathology, The Mount Sinai Hospital; 5Icahn School of Medicine at Mount Sinai; 6Department of Neurosurgery, The Mount Sinai Hospital; 7Department of Pathology, NYU Langone Medical Center Introduction: IDH-mutant astrocytomas carry significantly better prognosis compared to their IDH-wildtype counterpart. EGFR amplification is associated with aggressive behavior and regarded as a molecular feature of glioblastoma. Although rare, IDH-mutant astrocytomas with EGFR amplification exist but remain poorly understood. Report: We report the clinical and molecular profile of four IDH-mutant glioblastomas (grade4 astrocytomas) with EGFR amplification, evaluated at two institutions between 2015-2020. Case1 was a 59-year-old male with a right frontal tumor with IDH1R132H, TP53, and PIK3CA mutations; EGFR, PDGFRA, and KIT amplifications; and methylated MGMT; who expired two days after initiating temozolomide treatment. Case2 is a 15-year-old male with a left frontal tumor with IDH1R132H, ATRX, TP53, and PIK3CA mutations; EGFR amplification; loss of MTAP and CDKN2A/B; and methylated MGMT; who received temozolomide and adjuvant proton beam radiation and currently has radiographic findings suspicious for CSF dissemination. Case3 is a 28-year-old male with Charcot Marie Tooth syndrome and a left frontoparietal tumor with IDH1R132H, EGFR amplification, and unmethylated MGMT; lost to follow up after Stupp-protocol treatment. Case4 is a 37-year-old male with a left parietal tumor with IDH1R132H and ATRX mutations; EGFR amplification; and unmethylated MGMT; who received procarbazine with 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea and adjuvant radiation, currently in a stable condition. DNA methylation profiling confidently clustered all tumors with “IDH-mutant High Grade Astrocytoma” (0.99 0.997, 0.98, and 0.99 classification score, respectively). Review of the literature confirmed the occasional occurrence of EGFR-amplified IDH-mutant astrocytomas/glioblastomas in four published studies, at 8-19% frequency from total IDH-mutant cases. Most IDH-mutant EGFR-amplified gliomas were MGMT-methylated and showed significantly lower overall survival only in the co-presence of CDKN2A/B loss and/or MYC amplification. Conclusion: Co-existence of IDH mutation and EGFR amplification is occasionally seen in gliomas and should be considered in forthcoming classification paradigms. In our small series, all tumors carried the epigenetic signature of an IDH-mutant astrocytoma. 58 Towards a Single-assay Approach for Routine Infiltrating Glioma Diagnostics Using a Targeted Next-Generation Sequencing Panel Cheyanne Slocum1, James Solomon2, Martin Wells3, Susan Mathew2, Benjamin Liechty2, Wei Song2, David Pisapia2 1Weill Cornell Medical College; 2Department of Pathology and Laboratory Medicine, Weill Cornell Medicine; 3Department of Statistics and Data Science, Cornell University Given the current approach to CNS tumor diagnostics that integrates both histological and molecular features, an increasing number of molecular alterations are being considered as diagnostic criteria for the classification and grading of infiltrating gliomas. This has increased the applicability of targeted next generation sequencing (NGS) to routine CNS tumor diagnostics. We investigated whether diagnostic efficiency could be increased using a targeted NGS panel as a single-modality approach, replacing some of the conventional tools used as part of our standard workup including FISH for 1p/19q and EGFR alterations, and immunohistochemistry for IDH1, p53, and ATRX. Using the Oncomine Comprehensive Panel v2 over 157 infiltrating gliomas, we found that this modality is superior to IHC in detecting IDH1/2 and TP53 mutations. In addition, the Oncomine-based mutational profile is predictive of ATRX status, without directly assessing this gene, in 92% of cases and we find that ARTX immunohistochemical staining rarely provides additional diagnostically relevant information. Based upon copy number analysis of panel genes residing on chromosomes 1 and 19, we are able to determine 1p/19q co-deletion status with 100% sensitivity and 98% specificity relative to FISH. In addition, detection of EGFR amplification is 100% sensitive relative to FISH, and CDKN2A loss is also robustly detected. Over and above the ability to replace alternative diagnostic assays in routine settings, the NGS panel employed here additionally detected alterations with potential prognostic and/or therapeutic relevance including CDK4 amplification and both common and uncommon fusion transcripts, including FGFR3-TACC3 and ETV6-NTRK2. Based on this work, we advocate for the expanded use of targeted panels as stand-alone assays where possible to reduce diagnostic assay redundancy and to streamline the workup of infiltrating gliomas, particularly in laboratories that already employ NGS panels. 59 Correlation of Intraoperative Confocal Laser Endomicroscopy Imaging to Pathology for Brain Tumors Jennifer Eschbacher1, Irakliy Abramaov1, Evgenii Belykh2, Alexander Dru3, Smith Kris4, Randall Porter4, Andreq Little4, Michael Lawton4, Mark Preul4 1St. Joseph's Hospital/Barrow Neurological Institute; 2Rutgers University; 3Department of Neurological Surgery University of Florida; 4Barrow Neurological Institute Objective: This study assesses the feasibility of a FDA-approved confocal laser endomicroscope (CLE) system for intraoperative real-time in vivo identification of abnormal tissue during resection of intracranial neoplasms in 30 patients (21/30 patients acquired). Methods: The CLE system was used in 21 patients to date after intraoperative intravenous injection of fluorescein sodium (FNa). Tissue from imaged sites were acquired using neuronavigation and processed into hematoxylin and eosin (HE) stained slides for direct comparison. Images were classified as interpretable or noninterpretable, based on whether the images showed the presence of histopathologic features similar to the matched HE stained tissue biopsy. These features included cellularity, architecture, nuclear atypia and/or vascularity. A remote system was utilized for 4 cases (Surgery-Pathology Workplace) which allowed intra-operative real-time images to be remotely transmitted to the pathologist. Results: CLE images (7690 total, 366 avg/case) were obtained on all 21 patients (8 male; 13 female; mean age 56.3 yrs). Diagnoses included 6 gliomas, 5 meningiomas, 5 metastases, 1 perineuroma, 1 pineocytoma, 1 radionecrosis, 1 hemangioblastoma, 1 schwannoma, 1 choroid plexus papilloma. Mean duration of intraoperative CLE system use was 6 minutes/case (range 3.1–11.5 min). CLE images were correlated with 32 biopsy specimens from 21 patients. An average of 34.9% of CLE images were interpretable per patient; overall, 2481 vs. 5209 images were interpretable vs. uninterpretable. After CLE initiation, 6 images (average; mean duration 7.0 sec) were acquired before identification of the first interpretable image. For each case, CLE was 100% sensitive for identification of histologically abnormal tissue which shared features with the HE stained section. Surgery-Pathology Workplace allowed intra-operative real-time image remote display and interpretation sharing between the pathologist and neurosurgeon. Conclusions: This ongoing study demonstrates the feasibility of CLE to guide neurosurgery-pathology intraoperative tissue interpretation during tumor resection which may significantly impact surgeon-pathologist workflow in the OR. 60 Atypical Pediatric Glioneuronal Tumor with FGFR1-TACC1 Fusion Elena Daoud1, Jenny Weon1, Jack Raisanen1, Dennis Burns1, Kimmo Hatanpaa1, Jason Park2, Shannon Kelley2, Veena Rajaram2 1University of Texas Southwestern Medical Center; 2Dallas Children's Medical Center Pediatric CNS tumors are biologically distinct from their adult counterparts and may be defined by their molecular alterations. We report a recurrent glioneuronal tumor in a 3-year-old female initially presenting with seizures and arm weakness. MRI revealed a well-defined 1.6 cm solid enhancing mass with a 2.9 cm cystic component in the right precentral cortex. Five weeks later, the patient presented with a 5.9 cm right frontal hematoma and underwent a craniotomy for evacuation and mass resection; a small rim of residual tumor was seen on post-operative imaging. Histology demonstrated a low-grade glioneuronal tumor that could not be definitively classified but had foci suggestive of dysembryoplastic neuroepithelial tumor and a low Ki-67 proliferative index. Notably, no mitotic figures, necrosis, Rosenthal fibers or eosinophilic granular bodies (EGBs) were identified. The tumor grew slowly, and the patient had intermittent seizures. Three years later, family elected to undergo additional debulking. The resection specimen showed a circumscribed neuroepithelial tumor with multifocal calcifications in the adjacent brain. Most of the tumor showed pleomorphic epithelioid glial cells (some with pericellular reticulin deposition), occasional dysmorphic neurons, and a few small foci similar to prior resection. Areas of desmoplasia and EGBs were present. While no necrosis or microvascular proliferation was identified, the mitotic index was multifocally increased to 6/10 HPFs and the Ki-67 proliferative index was approaching 13%. Molecular studies demonstrated an FGFR1-TACC1 fusion, which has been previously reported in a variety of low-grade and high-grade CNS tumors. However, this fusion has not been reported in a mixed glioneuronal tumor. A clinical trial with targeted anti-FGFR therapy may be a treatment option for this patient. This case suggests that pediatric neuroepithelial tumors with mixed histology can harbor the FGFR1-TACC1 fusion. Given the high proliferative index in the residual/recurrent tumor, the grading may depend on its biologic behavior. 61 Recurrent Pediatric Glioma with EP300-BCOR Fusion Eric Goold1, Daniel Sullivan2, Arie Perry2, Joshua Klonoski1, Lorraina Robinson1, Sanda Alexandrescu3, Walter Devine2, Mouied Alashari1, Angelica Putnam1 1University of Utah Department of Pathology; 2University of California, San Francisco; 3Boston Children's Hospital Patient History: A 14 year old boy with autism spectrum disorder presented with progressive verbal skill decline over a few years. He presented with a 2-minute tonic-clonic seizure with postictal aphasia. Imaging: A contrast-enhanced MRI demonstrated a 2.6 x 2.8 x 3.2 cm mass in the left frontal opercular region. The mass had minimal intrinsic enhancement and the overlying frontal bone demonstrated remodeling suggestive of a chronic process. Mass effect on the adjacent sulci was mild with no midline shift or ventricular compression. EEG showed interictal epileptiform discharges in the left frontal region. Surgery/pathology: Surgery was performed for medically refractory seizures. Outside consultation resulted in a diagnosis of a low-grade oligodendroglial neoplasm, favoring a dysembryoplastic neuroepithelial tumor. Follow up: Follow-up imaging at 2 years showed a 2 cm area of recurrence along the posterior margins of the resection cavity. A second surgical resection was performed. Outside consultation showed a histologically similar tumor, but now with increased mitotic activity. The USCF500 panel demonstrated a rare EP300-BCOR fusion. Methylomics and genetic testing performed at the NIH demonstrated a methylation class suggestive of “CNS High Grade neuroepithelial tumor with BCOR alteration” as well as an MSH6 S503C variant of undetermined significance. The final diagnosis was pediatric glioma with high grade features and EP300-BCOR fusion, clinically recurrent. Subsequent testing of the original specimen confirmed the EP300-BCOR fusion. The EP300-BCOR fusion consists of a fusion product of the corepressor BCL-6 and the histone acetyltransferase EP300 leading to aberrant epigenetic regulation. This fusion has been reported in 3 other recurrent pediatric gliomas. Importantly, it is suggested to be associated with recurrence and worse prognosis. Treatment for patients with gliomas harboring this fusion is not well standardized; however, when detected, it may necessitate more aggressive management. Greater experience with this tumor type is needed. 62 Heterogeneous High Grade Pineal Parenchymal Tumor: A Diagnostic, Grading, and Molecular Challenge Merryl Terry1, Aaron Spalding2, Kaylyn Sinicrope2, David Sun2, Fausto Rodriguez3, Hilary Highfield2 1University of Louisville, Department of Pathology; 2Norton Neuroscience Institute, Pathology; 3Johns Hopkins Hospital, Department of Pathology Pineal gland neoplasms are infrequent, including those with a pineal parenchymal phenotype. Pineal parenchymal tumors (PPTs) exist on a spectrum, including the well-differentiated pineocytoma (WHO grade I), the pineal parenchymal tumor of indeterminate differentiation (PPTID, WHO grades II and III), and the primitive pineoblastoma (WHO grade IV). Grading of PPTs has historically proven difficult, particularly for those tumors which fall in the indeterminate category. In addition, there is inconsistent association between histologic grade, appropriate treatment, and patient outcomes. The molecular basis of PPTs is not yet well-elucidated. The authors present a case of a large, heterogeneous, high grade pineal parenchymal tumor with review of the current PPT grading schema and known molecular alterations. A 32-year-old male presented with hydrocephalus. An MRI brain showed 3.5 x 3.4 x 3.1 cm enhancing extra-axial pineal region mass indenting the floor of the third ventricle with ventriculomegaly. CSF cytology demonstrated atypical cells, while total spine MRI was without additional metastases. Biopsy and subsequent partial surgical resection demonstrated a vascular heterogeneous pineal parenchymal tumor, with both well-differentiated and high grade areas. The tumor was immunoreactive for synaptophysin, with retention of RB1 protein and INI-1 nuclear expression. GFAP and H3 K27M immunohistochemistry were negative. Proliferative activity was variable, with up to three mitotic figures in a single high power field, with a corresponding increase in Ki-67 proliferative index, indicative of a high grade pineal parenchymal tumor. Necrosis was absent. Molecular testing revealed the tumor to be wildtype for DICER1, POU4F2, and HOXD13. The combination of these findings supported a diagnosis of pineal parenchymal tumor of intermediate differentiation, corresponding to a WHO Grade III. 63 Diffuse Large B-Cell Lymphoma Resembling Primary CNS Lymphoma with Exclusive Involvement of Peripheral Nerves M. Adelita Vizcaino1, Paul Kurtin1, Caterina Giannini1 1DLMP, Mayo Clinic, Rochester MN While primary CNS lymphoma (PCNSL) and systemic diffuse large B-cell lymphoma (DLBCL) at times extend to cranial/peripheral nerves, involvement limited to peripheral nerve is very rare. We report the clinico-pathological findings of two DLBCL patients with involvement limited to peripheral nerve showing an unusual and peculiar phenotype. Patient 1 presented with involvement of the left brachial plexus and a year later of the right trigeminal nerve, while patient 2 of the left lumbosacral roots and plexus. Neither patient was immunosuppressed. Patient 1, treated with chemoradiation and autologous bone marrow transplant, continued to have disease limited to nerves after 2 years. Patient 2 is currently undergoing primary therapy. In both cases, lymphoma cells diffusely involved the endoneurium with a distinct pattern alongside axons within the Bunger bands accompanied by severe axonal degeneration. Both lymphomas were non-germinal center B-cell by the Hans algorithm, showing CD20, BCL6, MUM1 and MYC immunoexpression. Case 2 also showed BCL2 immunoreactivity. Case 1, not a BCL2/MYC protein “double expresser”, showed BCL6 gene rearrangement and was negative for MYD88 L265P by allele-specific PCR. Case 2, a “double expresser”, was negative for EBER ISH, negative for BCL2, BCL6, MYC and MYC/IGH translocations by FISH, and positive for MYD88 L265P. Collagen IV highlighted the basement membrane delimiting Bunger bands, inside which numerous CD68/CD163 positive macrophages were present. These two cases of DLBCL demonstrate a distinctive pattern with exclusive peripheral nerve involvement, which to our knowledge has not yet been described. The phenotypic and genetic features of these lymphomas resemble those involving immune privileged sites, such as PCNSL. Why the clonal B-cells show distinctive targeting to peripheral nerves, possibly reflecting expression of specific stimulating antigens, remains to be determined. 64 Extraneural Metastasis of Glioblastoma and TP53 Pathogenic Variants Xiaoming Zhang1, Levon Katsakhyan1, Virginia LiVolsi1, Jacquelyn Roth1, Christopher Rassekh1, Stephen Bagley1, MacLean Nasrallah1 1University of Pennsylvania Extraneural metastases of glioblastoma are rare, with an unknown biological. To explore the potential genomic drivers of extraneural metastasis in glioblastoma, we present the molecular features of four extraneural metastatic glioblastomas seen at our institution, and review and analyze previously reported cases that had available molecular characterization. In addition to our 4 cases, 39 patients from 32 publications are reviewed. In addition, the molecular profiles of glioblastoma cases with extraneural metastasis and of the general glioblastoma population are compared using genomic data from 577 glioblastoma samples in The Cancer Genome Atlas database (TCGA). We found that 66.7% (20/30) of the cases with extraneural metastasis that were tested for TP53 changes had at least one TP53 pathogenic variant detected in either one or both primary and metastatic tumors. In contrast, TP53 mutation was significantly less frequent in the unselected glioblastoma from TCGA (22.6%, 54/248) (p = 0.000). In addition, O-6-Methylguanine-DNA Methyltransferase (MGMT) promoter methylation was more common in unselected TCGA glioblastoma cases (48.6%, 170/350) than in cases with extraneural metastasis (28.6%, 6/21), although not statistically significant. Similarly, IDH mutation is an extremely rare occurrence in GBMs with extraneural metastasis; only one case definitively harbored an IDH1 (p.R132H) mutation in our analysis. Our findings not only provide potential biomarkers for earlier screening of extraneural metastasis, but could also suggest clues to understanding biologic mechanisms underlying glioblastoma metastasis, and for the development of therapeutic modalities. 65 Multinodular Vacuolating Neuronal Tumor Associated with Corticobasal Degeneration Shows Relative Exclusion of Tau Pathology Andrew Gao1, Blas Couto2, Ivan Martinez-Valbuena3, Ain Kim3, Seojin Lee3, Anthony Lang2, Gabor Kovacs4 1Laboratory Medicine Program, University Health Network; 2Shulman Movement Disorders Clinic, Toronto Western Hospital; 3Tanz Centre for Research in Neurodegenerative Disease, University of Toronto; 4Department of Laboratory Medicine and Pathobiology, University of Toronto Introduction: Multinodular vacuolating neuronal tumour (MVNT) is a recently described neoplasm or hamartoma characterized by multinodular growth of an abnormal population of vacuolated neuronal cells, variably associated with epilepsy. Methods: We investigated an autopsy case of asymptomatic MVNT in a patient with 4R-tau proteinopathy corticobasal degeneration (CBD) using immunohistochemistry for tau antibodies targeting different phosphorylation, conformational, and isoform epitopes. Results: A 65-year-old man presented with gait apraxia, unilateral spasticity, and bradykinesia and deceased 8 years later. Incidentally, a multinodular lesion was discovered in the left frontal lobe on neuroimaging. At autopsy, the lesion extended from the periventricular white matter to the deep layers of the neocortex. Lesional cells showed neuronal morphology with vacuolation and expressed markers of both neuronal (synaptophysin) and glial (Olig2) lineage, consistent with MVNT. Neurodegenerative changes characteristic of CBD, including atrophy, neuronal loss, and gliosis of the frontotemporal lobes, ballooned neurons, and extensively distributed neuronal tau pathology, oligodendroglial coiled bodies, threads, and astrocytic plaques on tau immunostaining were seen. While the MVNT showed a similar epitope profile of tau-immunoreactivity (tau-ir) as the surrounding brain parenchyma, tumour nodules showed a marked relative reduction in tau-ir process density and absence of hallmark tau-ir lesions of CBD. Conclusions: We describe a rare coincidence of MVNT and CBD. Although MVNT nodules show a similar epitope profile of tau-ir, the decreased density may indicate that the distinct cellular composition of MVNT inhibits the generation/propagation of pathological tau into tumour nodules, with implications for the understanding of tau proteinopathy pathogenesis. 66 Final Histopathologic Diagnoses of Preoperatively Diagnosed Pituitary Macroadenomas Kanish Mirchia1, Kavya Mirchia1, Ola El-Zammar1, Christine Fuller1 1SUNY Upstate Medical University Pituitary adenomas comprise >80% of sellar region masses in most large series, the remainder consisting of craniopharyngiomas, benign cysts, inflammatory lesions, meningiomas, metastases, chordomas, and other rare entities, including posterior pituitary tumors. This review documents the rate of discordance between final histopathology and clinicoradiographic impression in cases with preoperative diagnosis of “pituitary macroadenoma” encountered from 2017 to 2020 at our tertiary care center. All cases with a preoperative diagnosis other than “pituitary adenoma” were excluded. One case with a prior clinical diagnosis of pituitary adenoma, but excision post-therapy was also included and considered to represent post-treatment involution. Of the 86 cases reviewed, 72 (83.7%) were consistent with the clinicoradiographic assessment and had a final histopathologic diagnosis of pituitary adenoma. The remaining 14 discordant cases (16.3%) were comprised of benign pituitary tissue (35.7%; n=5), necrotic tissue (21.4%; n=3), inflammatory lesions including one case of lymphocytic hypophysitis (21.4%; n=3), hyperplastic pituitary tissue (7%; n=1), inflammatory process with IgG4-predominant plasma cells (7%; n=1), and spindle cell oncocytoma (7%; n=1). In all but one case with a discordant clinicoradiographic-histologic diagnosis, the intraoperative diagnosis and final diagnosis were in agreement. One 66-year-old female with acromegaly and elevated serum IGF-1 levels was preoperatively diagnosed with pituitary adenoma. Intraoperative via touch preparation was interpreted as pituitary adenoma, whereas the final histology showed only nodular hyperplasia without a definitive adenoma. This review emphasizes the fact that a small proportion of patients with sellar lesions receiving clinicoradiographic diagnoses of pituitary adenoma will in fact harbor alternate histologic findings, including a variety of neoplastic and non-neoplastic lesions. Surgical sampling yielding normal pituitary tissue may well be contributing to some of this discordance. 67 Characterization of Medulloblastomas Presenting as Primary Leptomeningeal Involvement: Case Report and Literature Review Ryan Rebbe1, Jolee Suddock1, Jon Hallstrom1, Lauren Dvorscak1, Karen Santa Cruz1 1University of New Mexico Medulloblastomas are malignant neuroepithelial tumors that typically arise in the posterior fossa of children. These tumors are known to involve the subarachnoid space and disseminate throughout the leptomeninges. Comparatively, a primary leptomeningeal presentation is controversial and exceedingly rare. A comprehensive literature review revealed six case reports of medulloblastomas identified as primary leptomeningeal involvement without a prominent cerebellar mass lesion. To date, this is the second case report to discuss the molecular alterations accompanying this unique presentation. A 25-year-old woman presented to the hospital with difficulty ambulating, headaches, weakness, and difficulty urinating. CT and MRI demonstrated leptomeningeal enhancement without a primary intra-axial or peripheral mass. Subsequent biopsy revealed sheets of atypical hyperchromatic cells with minimal cytoplasm. The neoplastic cells were positive for chromogranin and synaptophysin and negative for pan-keratin and CD30. The patient rapidly declined and unfortunately died after one cycle of chemotherapy. Autopsy, including dedicated neuropathologic examination, confirmed primary leptomeningeal involvement without intra-axial mass. Immunohistochemical stains showed the neoplastic cells to be positive for synaptophysin, chromogranin, and INSM1. INI-1 was intact and a Ki-67 proliferation index was estimated at 10%. Negative stains included EMA, Myogenin, DUX4, TTF-1, Desmin, SMA, CD99, H3K27M, and tyrosine hydroxylase. Beta-Catenin showed diffusely weak cytoplasmic staining without nuclear staining. Molecular studies revealed methylation class medulloblastoma SHH A and no mutations in TP53. Subgroup SHH-activated and TP53-wildtype is reported to have a more variable clinical outcome compared to the higher risk SHH with TP53 mutations. While no TP53 mutation was detected, there was a promoter variant of TERT (c.1-124C>T). GAB1 and YAP1 staining were inconclusive, but not inconsistent with SHH activation. Outcomes from additional cases are required to further evaluate the significance of these molecular findings in relation to this unique presentation. 68 Primary Central Nervous System Histiocytic Sarcoma Arising in the Clivus Ivette Perez1, Murat Gokden1, John Day1, Hadi Yaziji2, Sergio Pina-Oviedo1 1University of Arkansas for Medical Sciences, Little Rock, Arkansas; 2Vitro Molecular Laboratories, Miami, Florida Introduction: Histiocytic sarcoma (HS) is a rare malignant neoplasm of hematopoietic origin that commonly arises in lymph nodes, intestinal tract, skin and soft tissue. The incidence of primary central nervous system histiocytic sarcoma is rare with only 39 cases reported in the literature. We describe a case of histiocytic sarcoma arising in the clivus, which has not been previously reported at this location to the best of our knowledge. Case: A previously healthy 56-year-old man presented with complaints of headaches and focal neurologic symptoms. Imaging demonstrated a T1-hyperintense and contrast-enhancing mass measuring 2.3 x 1.2 x 0.3 cm involving most of the sphenoid bone, extending inferiorly from the inferior sella turcica to the distal clivus. An endonasal transsphenoidal resection was performed. Histologically, a neoplasm with epithelioid and spindled morphology was identified. Focal areas of high-grade atypia, frequent mitoses, and necrosis were present. The neoplastic cells were immunopositive for CD68 and lysozyme, variably positive for CD4, CD45 and CD163, and negative for markers of epithelial, melanocytic, lymphoid, myeloid, muscle, and dendritic cell origin. Expression of PD-L1 by immunohistochemistry and molecular testing for BRAF V600E mutation were negative. Despite aggressive surgical measures, recurrence was noted less than two weeks after the surgery. The patient refused radiation therapy and succumbed to his illness three months after initial presentation. Conclusion: This report contributes to the English literature showing the first reported case of primary HS arising from the clivus to the authors’ knowledge. HS sarcoma has a poor prognosis and immunohistochemical stains are necessary to confirm the diagnosis and exclude mimics. Unfortunately, experience is limited with this highly-malignant neoplasm due to small number of cases reported, necessitating further research to improve clinical outcomes through targeted therapies. Infectious/Inflammatory 69 Cladophialophora bantiana Brain Abscess: Clinicopathologic and Radiologic Findings Kyriakos Chatzopoulos1, Kathryn Eschbacher1, Pooja Gurram1, Lorenzo Rinaldo1, Amber Milone1, Derek Johnson1, Aditya Shah1, Nancy Wengenack1, Audrey Schuetz1, Ian Parney1, Caterina Giannini1, Jorge Trejo-Lopez1 1Mayo Clinic Cladophialophora bantiana, a ubiquitous dematiaceous fungus, is an uncommon pathogen that infects the central nervous system of immunocompetent or immunosuppressed patients. An 82-year-old man, with recent onset headache and fatigue, was found to have a 4.2 x 3.4 x 3.2 cm right frontal lobe rim-enhancing intra-axial mass with restricted diffusion and extensive surrounding edema, most suspicious for glioblastoma or bacterial abscess. Surgical resection of the lesion was performed via a right frontotemporal craniotomy. Following intraoperative aspiration, which yielded green purulent fluid, the lesion was circumferentially dissected from the surrounding brain and removed. Histologic examination of the resection specimen revealed multifocal necrotizing granulomatous inflammation with pigmented fungal hyphae highlighted by Grocott’s methenamine silver (GMS) and Fontana-Masson histochemical stains. Culture of the aspirate, plated to inhibitory mold agar (IMA), grew many colonies at day 6. A cellophane tape prep showed darkly pigmented dematiaceous hyphae with very long chains of dark spindle shaped conidia, suspicious for Cladophialophora bantiana, which were seen microscopically and were confirmed by D2 rDNA sequencing. Post-operatively the patient was treated with oral voriconazole 200 mg twice daily, combined with intravenous liposomal amphotericin B at 5mg/kg daily for a week until therapeutic levels of voriconazole were achieved. He remained neurologically intact and had an uneventful post-operative course, discharging 9 days after the initial diagnosis with close follow up. This case highlights the importance of multi-disciplinary care approach in patients with Cladophialophora bantiana CNS infection. Because of the rarity of this infection it is not often included in the differential diagnosis but should be considered in infectious brain abscesses and when dark fungal hyphae are seen on hematoxylin and eosin. 70 Co-infection of SARS-CoV-2 and Central Nervous System (CNS) Tuberculosis in the CNS Joseph Fullmer1, Seyedalireza Fatemi1, Mustafa Deebajah1, Olabisi Afolayan-Oloye1 1Beaumont Health, Department of Pathology, Royal Oak, Michigan CNS symptoms and complications occur in individuals with SARS-CoV-2 infections, but relatively few studies have demonstrated the detection of the virus particles in the CNS. To our knowledge, there are no extensive studies on co-infection with Mycobacterium tuberculosis (MTB) in the CNS. We present a previously healthy five-year-old female child with a 6-day duration of fever and severe headache after amoxicillin treatment for group A streptococcal pharyngitis. Chest radiograph was clear. Both parents had respiratory tract infections recently and SARS-CoV-2 IgG was positive after recovery. Head CT scan on day 10 was normal. Meningitis/encephalitis nucleic acid amplification panel using FilmArray ME was negative. SARS-CoV-2 was not detected in the CSF via RT-PCR. CSF bacterial culture was sterile. Day 15 she became lethargic and developed asymmetric pupils with enlargement of the ventricles but SAR-CoV-2 RNA was not detected. She deteriorated, developed severe encephalopathy with minimally reactive, dilated pupils. On day 30, MRI showed edema, cerebellar tonsillar herniation and lack of normal flow at the circle of Willis. A midline suboccipital craniectomy and C1 laminectomy revealed herniated, necrotic, edematous cerebellum. She expired on day 32. Nasopharyngeal swabs were positive for SARS-CoV-2 RNA. Tracheal aspirate grew MTB. Cerebellar brain biopsy was positive for both SARS-CoV-2 RNA (using CDCqPCR) and MTB complex DNA. On histopathology, there were patchy areas of necrotizing granulomatous inflammation and severe vasculitis. Numerous acid fast bacilli were identified, confirmed to be tuberculosis complex via PCR. Ultrastructural studies on material from the brain noted vesicles consistent with SARS-CoV-2 viral particles. A source for the tuberculous infection was not identified; all family contacts had negative interferon-gamma release assays, normal chest radiographs, and no travel history; it is favored to be community based. When she acquired SARS-CoV-2 infection, this may have contributed to the CNS spread of the mycobacteria. 71 The Spectrum of HIV/AIDS Related Neuropathology Encountered in Neurosurgical Practice in Sri Lanka Dewa Lal1, Depal Attanayake2 1University of Colombo; 2National Hospital of Sri Lanka Background: HIV/AIDS is gaining an increasing interest in Sri Lanka as the incidence is growing up. Cerebral Infections and lymphomas are well recognized neurosurgical complications of HIV/AIDS. Currently screening for HIV infection is not routinely carried out on these patients unless the clinical picture is suggestive the possibility of HIV infection. The objective of this study is to evaluate the extent of HIV/AIDS related neurosurgical disease spectrum in Sri Lanka. Methods: HIV status of the sexually active patients who underwent neurosurgical interventions for HIV/AIDS related cerebral pathology over 3 years were evaluated using standards laboratory diagnostics. This was done as a part of the clinical management of the patients and data related to patient’s identity was not included in study. Results: 59 patients (26 females and 33 male, age between 24 to 58 years) have undergone neurosurgical interventions (aspiration, biopsy, excision, debulking) for HIV/AIDS related cerebral pathology. Bacterial abscess, fungal abscess, tuberculous lesions, Toxoplasmosis and lymphoma were the pathology among 26, 04, 08, 09 and 12 patients respectively. HIV infection was diagnosed in one patient with bacterial abscess (3.8%), one patient with fungal abscess (25%) and three patients with toxoplasmosis (33%). No HIV detected in patients with tuberculosis and lymphomas. Conclusion: HIV/AIDS is unlikely to be a significant predisposing factor for cerebral tuberculosis and lymphomas, but it is a definite predisposing factor for fungal infections and toxoplasmosis of the brain. Therefore routine screening for HIV status among patients with cerebral fungal infections and toxoplasmosis is recommended for Sri Lankan population. 72 Parasitic Neoplasm Arising in a Patient with Neurocysticercosis Cheyanne Slocum1, Mark Souweidane2, Philip Stieg2, David Pisapia3 1Weill Cornell Medical College; 2Department of Neurological Surgery, Weill Cornell Medicine; 3Department of Pathology and Laboratory Medicine, Weill Cornell Medicine Taenia solium, the cause of neurocysticercosis, represents one of the more common infectious etiologies encountered in a routine neuropathology service, however little is known about the neoplastic potential of this organism. Here we report the case of a 43-year-old woman who initially presented with clinical symptoms and radiographic findings that were attributed to a frontal arachnoid cyst. While initially managed conservatively, the cyst was reassessed 8 years later in the context of worsening headache, and surgical resection was pursued. A diagnosis of neurocysticercosis was rendered based on the usual parasitic histology in addition to confirmatory PCR analysis detecting T. solium DNA. However, in addition, clusters of atypical, and primitive-appearing cells within the parasitic organism were observed, consistent with a neoplastic process. We noted histologic resemblance of this cell population with those seen in a 2015 New England Journal of Medicine case report detailing the neoplastic transformation of cells derived from the parasite Hymenolepis nana, another tapeworm, that became widely metastatic in an immunocompromised human host. In our case, there was no evidence of neoplastic disease outside the confines of the parasitic parenchyma or anywhere else in the patient. The patient was given a treatment of steroids and albendazole for 6 months and at last known follow-up exhibited no further disease progression. While several parasitic infections have been closely linked to certain cancers, such as Schistosoma haematobium and bladder cancer, and there have been rare reports such as that referenced above of parasite-derived neoplasms affecting humans, to our knowledge this is the first description of neoplastic transformation of T. solium in a human patient. The clinical implications of such a neoplasm seemingly confined to the parasite are unknown, but we suggest that if seen such a phenomenon should be recognized and reported as a potential concern, particularly in the immunocompromised setting. 73 Cranial Hypertrophic Pachymeningitis and Granulomatosis With Polyangiitis: A Case Report And Review Of The Literature Yuan Rong1, Nirag Jhala1 1Temple University Hospital Introduction: Hypertrophic pachymeningitis (HP) is a rare condition characterized by localized, multifocal or diffuse thickening of the dura mater intracranially and/or along the spinal column. The pathogenesis of non-infectious HP is unclear. An autoimmune mechanism has been strongly implicated for such cases and use of immunosuppressive and/or steroid therapy has been beneficial. Here we report a case of HP and granulomatous inflammation of an enlarged left lacrimal gland with positive p-ANCA. Case report: A 31-year-old female initially presented with left upper eyelid swelling. A biopsy of lacrimal gland demonstrated granulomatous inflammation. Two months later, the patient developed fever, leukocytosis, dizziness and bilateral arm numbness. Brain MRI was significant for irregular patchy meningeal thickening and enhancement as well as enlargement of the left lacrimal gland. Serologic testing showed elevated c-reactive protein, erythrocyte sedimentation rate and positive for p-ANCA. A dura biopsy revealed granulomatous inflammation and rare obliterated small vessels. Special stains were negative for microorganisms. IgG and IgG4 immunostains did not show increased IgG4 plasma cells or increased IgG4/IgG ratio. Theses results along with the clinical history and positive p-ANCA are most compatible with HP associated with granulomatosis with polyangiitis (GPA). Discussion: The differential diagnosis of noninfectious HP is broad including autoimmune diseases, sarcoidosis, neoplasm etc. Meningeal involvement by GPA is extremely rare (0.6%). CNS involvement is supposed to develop in later stages in most cases, yet it may occur as the initial manifestation. The neurological symptoms of our patient was resolved and brain imaging showed no active inflammation after receiving Rituximab and prednisone therapy. Conclusion: Dural enhancement is characteristic for HP and can represent a localized form of GPA, even in the absence of systemic symptoms and signs. Granulomatous manifestation affecting CNS structures necessitates a fast workup and therapeutic intervention to prevent or reduce potential damage. 74 CNS Involvement by Wegener’s Granulomatosis of Maxillary Sinus and Trigeminal Neuralgia: Acute Sensorineural Hearing Loss Sunil Manjila1, Nicholas Zacharewski2, Misha Movahed-Ezazi3, Jignesh Modi4, Susan Stocker Giles5, Marc Eisen3, Belachew Tessema3 1St. Vincent's; 2Hartford Hospital/Trinity College; 3Hartford Hospital; 4Hospital of Central Connecticut; 5Trinity Health Introduction: Vascular loops are anatomical variants of cerebellar arteries that lead to compression and ultimately demyelination of the trigeminal nerve. A concurrent cranial neuropathy with Wegner’s granulomatosis is common within the literature. However, cranial neuropathy as a sole, initial clinical symptom in Wegner’s granulomatosis patients is rare and only documented in few case reports. Case Report: A 25-year-old female patient presented with classic facial (left V2- V3) pain, refractory to medical therapy. The patient underwent microvascular decompression for management of trigeminal neuralgia. Intraoperatively, there were acute changes in BAER in addition to sensorineural hearing loss noted profoundly the following morning. Post-operatively her facial pain had completely disappeared. For her significant clinical hearing loss, she was started on oral steroids and her blood pressure was kept elevated to mean arterial pressure above 80 mm Hg. With subsequent intraaural injection of steroids, over a period of time her hearing improved. However, she complained of pressure in the ipsilateral maxillary sinus with subsequent imaging revealing destructive sinus lesions which were histologically proven to be Wegener’s granulomatosis. Discussion: Wegener’s Granulomatosis is a clinically rare form of vasculitis that can cause inflammation of blood vessels in the respiratory system, however the plethora of intracranial involvement is underreported. This is an anecdotal case of association versus causation of a rare vasculitic phenomenon in the setting of compressive cranial neuropathy. Conclusion: We present the rare case of double vascular loops causing trigeminal neuralgia and Wegener’s Granulomatosis in a 25-year-old female patient. The authors also highlight the recovery pattern of acute sensorineural hearing loss from surgery, with the intraaural injection of steroids and time. 75 Acute Disseminated Encephalomyelitis: An Unusual Fatal Case in a Young Adult Sindha Madhav1, Thomas Smith1 1University of Massachusetts Medical School Acute disseminated encephalomyelitis (ADEM) is an immune-mediated demyelinating disorder that may occur as a response to an infection or vaccination. It typically affects children, is self-limiting, and spontaneous recovery is the general rule. The diagnosis is based on a combination of clinical and radiological features and exclusion of diseases that can mimic ADEM. We report a fatal case of ADEM in a previously healthy 32-year-old man following a viral infection. The patient initially presented with altered mental status, headache and a seizure three weeks after being diagnosed with infectious mononucleosis. Serology confirmed the presence of elevated Epstein-Barr viral (EBV) IgM and IgG antibodies. Cerebrospinal fluid showed increased protein and lymphocytic pleocytosis. He rapidly became comatose and developed irreversible cerebral edema leading to brain death. Autopsy showed diffuse brain swelling with cerebellar tonsillar herniation. Microscopic examination revealed extensive perivenular mononuclear inflammation involving predominantly white matter throughout the brain and spinal cord. The perivascular inflammation consisted of CD3+ lymphocytes, mainly CD8+ with relatively fewer CD4+ cells. Many macrophages (CD68+) surrounded these vessels and often extended into adjacent white matter. Luxol fast blue staining showed focal myelin breakdown adjacent to involved vessels with myelin debris in scattered macrophages. No histologic features of encephalitis were present. The relatively few B lymphocytes present around vessels were negative for EBV (EBER). The histologic features were interpreted as most compatible with ADEM, likely precipitated by the patient’s viral illness. This case emphasizes that although ADEM typically has a relatively favorable clinical course, it may rarely be associated with rapid progression which may result in death due to cerebral edema and brainstem involvement. Peripheral Nerve/Muscle 76 Lipomatosis of the Nerve: A Rare Case with Diffuse Involvement of the Brachial Plexus Blake Ebner1, Kathryn Eschbacher1, Dragana Milosevic1, Megan Jack2, Robert Spinner2, Caterina Giannini1 1Mayo Clinic, Department of Laboratory Medicine and Pathology; 2Mayo Clinic, Department of Neurosurgery Lipomatosis of the nerve (LN) is a fibrolipomatous lesion characterized by overgrowth of mature adipose tissue within the epineurium surrounding and separating nerve fascicles, often associated with perineurial thickening and endoneurial pseudo-onion bulb formation mimicking intraneural perineurioma. LN is clinically characterized by progressive sensory loss and paresthesias, followed by pain and weakness involving most frequently the upper extremities and median nerve. As PIK3CA mutations have been recently reported in peripheral nerves from patients with LN with or without nerve territory overgrowth, LN is considered part of the PIK3CA-related overgrowth spectrum disorders. We report the autopsy findings of a 55-year-old woman, with a proximal LN, extensively involving the left brachial plexus associated with soft tissue overgrowth and macrodactyly. The patient experienced paresthesias and weakness involving the affected extremity. Premortem imaging demonstrated septate co-axial cable-like adipose infiltration of the brachial plexus and overgrowth of the ulna, third and fourth digits. Pathological examination revealed gross diffuse enlargement of the proximal and distal branches of the brachial plexus with extensive mature adipose tissue overgrowth, marked perineurial thickening and extensive endoneurial pseudo-onion bulb formation. By digital droplet polymerase chain reaction, we confirmed the presence of a common PIK3CA mutation (p.H1047R) associated with LN, limited to the involved territory. This case is an example of a rare presentation of LN with brachial plexus involvement, unilateral near complete upper extremity changes, and associated distal extremity soft tissue and osseous overgrowth. 77 ERBB2 (V777L) Mutation Causes Localized Hypertrophic Neuropathy: A Case Report Nima Sharifai1, Robert Bucelli1, Susan Mackinnon1, Robert Schmidt1, Joseph Corbo1 1Washington University in St. Louis Background: Localized hypertrophic neuropathy (LHN) is characterized by diffuse enlargement of individual nerves, owing to Schwann cell proliferation with true onion-bulb formation. The etiology of LHN is unknown, however there is evidence that a subset of cases are neoplastic in nature. Here we report a case of localized hypertrophic neuropathy resulting from an activating mutation in the kinase domain of HER2. Case Report: The patient is a 37-year-old woman with a 14-year history of right arm weakness and pain. Neuromuscular ultrasound showed massive and longitudinally extensive enlargement of nerves from the right brachial plexus into the right forearm. Nerve conduction studies showed findings compatible with a right brachial plexopathy/mononeuropathy multiplex, without primary demyelinating features. Nerves of the left upper limb were normal on ultrasound, but spinal MRI showed multiple enhancing masses along the bilateral spinal nerve roots and some intercostal nerves. The patient has no family history or clinical symptoms of neurofibromatosis, and no NF1, NF2, SMARCB1, or SPRED1 mutations on genetic sequencing. An ulnar nerve biopsy showed a hypertrophic peripheral neuropathy with onion bulb formation and foci of Schwannian proliferation, findings confirmed on electron microscopy. Targeted-next generation sequencing of the lesion revealed a mutation in ERBB2 (V777L). DNA sequencing from a salivary sample did not detect this or any other mutations in a panel of neuropathy-related genes, suggesting that the patient’s mutation arose somatically. Discussion: ERBB2 (V777L) is a well-studied activating mutation found in a range of neoplasms. This mutation was also recently reported in a hybrid nerve-sheath tumor. Furthermore, aberrant ERBB2-mediated signaling has been implicated in multiple forms of hypertrophic, demyelinating Charcot-Marie-Tooth disease. The findings in the current case suggest that activation of the HER2 pathway can cause LHN. 78 Blau Syndrome: Peripheral Neuropathy in a Rare Case Ravi Raghavan1, Karthik Bhuvaneswaran1, Nooshin Salehi2, Mahrnaz Hojjati1, Jeffrey Rosenfeld1 1Loma Linda University Medical Center; 2University of California Riverside Introduction: Blau syndrome (BS) is a rare systemic inflammatory disease characterized by early-onset granulomatous arthritis, uveitis and skin rash, due to a NOD2 (CARD15) gene mutation. Neurological manifestations are uncommon. This report highlights a rare manifestation of peripheral neuropathy in BS that responded to immunosuppression. Case presentation: This 36 year old male was diagnosed with BS at the age of 4 presenting with refractory uveitis, polyarthritis and a positive genetic test. He was treated intermittently with methotrexate until 9 years of age, but was lost to follow up. He presented again with new onset numbness, tingling, dysthesias and weakness of lower extremities, that progressed to bilateral foot drop, with numbness and weakness in upper extremities and face. Electrodiagnostic study was remarkable for mononeuritis multiplex. Screening tests were negative for TB, HLA, SPEP, UPEP but HBV core IgG were positive with negative HBV S Ag and PCR. Since neurological complications are unusual in this condition, a sural nerve biopsy followed. He was started on pulse dose corticosteroids along with IVIG therapy with noted improvement of his neuropathy. Results: H&E stained sections revealed patchy moderate perivascular infiltrates of CD3+T & CD20+ B lymphocytes, and few plasma cells, predominantly perineurial, with focal endoneurial involvement. Well defined granulomas were absent. Neurofilament-immunostained sections revealed moderate axonal depletion. On resin-embedded thin sections, moderate to severe depletion of myelinated axons, both large and small was confirmed. The majority of small myelinated fibers were absent on electron microscopy. Myelin ovoids were inconspicuous, and no significant sprouting was observed. Conclusion: Considering the history of BS, a genetically-determined inadequacy of immune/inflammatory response likely contributed to this patient’s progressive axonopathy. A possible role for HBV was excluded by immunohistochemistry, and the absence of immune complexes. No such peripheral neuropathic presentation has been reported in the literature on Blau syndrome 79 A Myopathy with Tubular Aggregates With Mitochondrial DNA Mutations: A Case Presentation Raul Rodríguez1, Darius Adams2, Ada Baisre1 1Rutgers-New Jersey Medical School; 2Atlantic Health System-Morristown Medical Center Tubular aggregate myopathy usually presents in childhood and progresses overtime. It is characterized by distal more than proximal muscle weakness, as well as pain, cramping and stiffness. Mutations in STIM1, ORAI1 and other less common genes have been described in these patients. We present the case of a 51-year-old man without a family history, who complains of a 15-year history of progressive muscle fatigue and weakness, worse in the lower extremities. 5-years later he also noticed leg cramping, particularly after seating for long periods of time, as well as his muscles being smaller. He also reports stiffness and soreness in the morning. On examination he showed muscle weakness, atrophy, and cramping with release of grip. His CK levels were modestly elevated to 313 U/L. A hearing test was performed and was normal. A muscle biopsy was ordered and H&E stained sections showed several subsarcolemmal basophilic inclusions. These inclusions were bright red with Gomori-Trichrome and stained strongly with NADH-TR and esterase, and were most consistent with tubular aggregates. COX negative fibers were not identified on a combined COX/SDH histochemical stain. A pathogenic mutation m.7471dupC, was identified in the MT-TS1 gene with ∼2% heteroplasmy. This mutation is usually seen associated with a phenotype of mitochondrial nonsyndromic hearing loss and deafness, and mitochondrial C-oxidase deficiency. Two other variants of unknown significance were also identified as follows: homoplasmic m.7472A>C, in the MT-TS1 gene and m.15995 G>A with ∼3% heteroplasmy in the MT-TP gene. It is not clear if the combination of m.7471dupC and m.7472A>C may act as a phenotypic modifier. The DMPK (DM1) gene did not harbor any repeat expansion. Variants of unknown significance were also identified in the MYOT, COL6A1 and RYR1 genes. To our knowledge this is the first report of a myopathy with tubular aggregates phenotype with a m.7471dupC MT-TS1 mutation. Ophthalmic Pathology 80 Black and Blue: Eyes and Dyes Raymond Sobel1, Jeff Nirschl1, Phoebe Hammer1, Russell Sanchez1, Suzann Pershing1, Christine Louie1, Jonathan Lin1 1VA Palo Alto/Stanford University School of Medicine A 92-year-old man had a history of hypertension, atrial fibrillation, prostate carcinoma, dementia, and ataxia. Six years prior to death he had cataract surgery of the right eye complicated by iris prolapse, iridodialysis, posterior capsular rupture and vitreous loss. Trypan blue (TBl) (∼100–200 microliters, 0.06%) was injected into the front of the eye during this procedure for lens capsule visualization. It was irrigated out of the eye within 30 seconds. He subsequently developed chronic corneal surface disease and bilateral glaucoma and was treated for ∼6 years with oral minocycline (50 mg bid), topical lubrication and latanoprost in both eyes. Autopsy demonstrated dense black pigmentation of the thyroid attributable to minocycline (Bann, 2014). There was blue-black discoloration of his cranial dura and of an old right parietal infarct. Microscopy demonstrated irregular streaks of blue ink-like pigment in the dura. The infarct had typical features with additional accumulation of brown/black granular pigment in macrophages. He also had cerebral atherosclerosis, Alzheimer disease, and cerebellar atrophy, possibly paraneoplastic. The right eye showed an intact artificial intraocular lens along with extensive loss of iris structures and an overlying scleral scar. Deeply pigmented uveal melanocytes in both eyes were likely secondary to latanoprost (Albert, 2008). Both retinas showed intense GFAP staining of the retinal nerve fiber layer and numerous CD163+ microglia, findings associated with glaucoma. The infarct discoloration was likely secondary to minocycline; dural pigmentation has not been associated with minocycline. When injected into animals, TBl binds dense collagen, particularly dura, and necrotic but not viable brain tissue (King, 1938). Although the TBl was grossly washed out of the eye, we speculate that a small amount may have entered this patient’s circulation during the traumatic cataract surgery. Thus, the precise causes of the discoloration are unclear and may be due to a combination of agents. 81 Visual Symptom Presentation of Intracranial Disease: Spectrum of Non-Stroke Lesions and Locations Marwan Majeed1, Brent Hoffman2, Christopher McMillan2, William Clark2, Mitchell Nash2, Wen Zhong3, K. Stuart Lee4, Jasmin Jo5, John Prenshaw6, Regis Hoppenot4, Richard Dalyia4, Karen Kelly1, Keith Tucci4, Philip Boyer1 1East Carolina University/Vidant Medical Center; 2Brody School of Medicine, East Carolina University; 3University of Pittsburgh Medical Center Presbyterian Hospital; 4Vidant Neurosurgery/Vidant Health; 5East Carolina University; 6White Eye Associates Ophthalmology Background: An eye-related disease process is most common in patients presenting with vision deficits but, in a subset, an intracranial disease is the culprit. Methods and Materials: Cases with intracranial disease presenting with vision deficits were compiled. Cases were selected to illustrate the range of non-stroke disease processes seen in various intracranial locations which can manifest with vision loss and to illustrate delays in diagnosis. Results: Twenty-two cases presenting with vision deficits with subsequent identification of an intracranial lesion were compiled. Ten cases were seen by an optometrist and/or an ophthalmologist prior to brain imaging studies; initial diagnoses included worsening myopia / hyperopia (with new eyeglass prescription), cataracts (with two patients undergoing surgery), diabetic or/and hypertensive retinopathy (with one patient undergoing vitrectomy), and retinal degenerative disease with a delay in head imaging studies. Lesions were associated with optic chiasm and/or nerve compression (10, meningiomas, pituitary adenomas, pituitary metastasis, Rathke cleft cyst, craniopharyngioma); intraaxial or extraaxial neoplasms disrupting optic tract or geniculocalcarine fibers or calcarine cortex (8, primary neoplasms (glioblastomas, pleomorphic xanthoastrocytoma, polymorphous low-grade neuroepithelial tumor of young), metastatic neoplasms, and a meningioma); and periventricular or intraventricular lesions leading to obstructive hydrocephalus and increased intracranial pressure, papilledema, and optic nerve and disc damage (4, autoimmune lymphoproliferative syndrome, medulloblastoma, meningioma, and hemangioblastoma). Conclusions: The primary goal of this project was to provide a survey of intracranial neoplasms that can manifest with vision deficits and 22 cases presenting with visual symptoms with an underlying intracranial neoplasm were compiled. In ten cases, eye-related diagnoses and treatment lead to a delay in obtaining imaging studies, correct diagnosis, and treatment. Given the potential for irreversibility of the visual deficits when such a delay occurs, there should be a low threshold for obtaining a screening brain scan when eye examination fails to fully explain visual symptoms. 82 An Uncommon Cause of Infectious Crystalline Keratopathy Sarah Edminster1, Kyle Hurth2, Rosemary She2, Maria Sibug-Saber2, Anna Mathew2 1Department of Pathology, LAC+USC Medical Center Program, Los Angeles, CA; 2Department of Pathology, Keck School of Medicine of USC, Los Angeles, CA Infectious Crystalline Keratopathy (ICK) is a rare corneal infection associated with hazy, branching stromal opacities in the cornea. ICK is usually secondary to gram positive cocci. Regardless of infectious etiology there is generally an absence of inflammation. There have only been a limited number of fungal ICK cases reported in the literature which include Cladosporium and Candida species. A 78-year-old male presented with history of corneal scar and later a corneal ulcer. He was eventually diagnosed with ICK and ∼3 weeks later the infiltrate had completely resolved. He was scheduled for a penetrating keratoplasty (PKP) after his macular edema and uveitis had been controlled. A week prior to surgery he presented with features highly suggestive of perforation which appeared to be sealed with bandage contact lens in place. He also received an intravitreal steroid injection 1 week prior to surgery. The patient underwent PKP and the patient cornea was not sent for culture. Upon histologic examination, the cornea demonstrated an epithelial ulcer with associated stromal thinning and minimal to absent inflammation. Numerous clusters of yeast were seen in areas of epithelial loss and within the corneal stroma. The presence of yeast forms was supported by GMS and PAS-fungal stains. The size, presence of budding, and their arrangement supported their identification as yeast with Candida Spp being a possibility. We report a unique case of ICK caused by fungi, adding to the limited number of reported cases in the literature. Most cases of ICK are caused by bacteria and are treated empirically with antibiotics. The purpose of this case report is to increase awareness of fungal causes of ICK, and to reiterate the importance of sending patient cornea for culture should there be a clinical suspicion of ICK to help improve patient outcomes. Other Topics 83 Data Elements and Tissue Procurement for COVID-19 Brain Banking Jerry Lou1, Mehrnaz Movassaghi2, Dominique Gordy2, Madeline Olson2, Elyse Singer3, Shino Magaki2, William Yong1 1Department of Pathology, University of California - Irvine SOM; 2Department of Pathology, DGSOM at UCLA; 3Department of Neurology, DGSOM at UCLA Coronavirus disease 2019 (COVID-19) frequently involves the central nervous system, manifesting as a spectrum of neurological disorders. A significant subset of patients may suffer from “Long Neuro-COVID” wherein they have persistent symptoms for months after recovery from the acute phase of the disease. Biobanks aimed at specifically studying Neuro-COVID are in the early stages of development. Brain banks that focus on other disorders such as HIV and dementia may also need to account for SARS-CoV-2 associated clinical complications and neuropathology in their cohorts. Adequate data collection of patient co-morbidities, clinical course, therapies, and neuropathological findings will facilitate meaningful analyses of the banked brains and other biospecimens. Timeline and methodology of COVID-19 testing (e.g. qRT-PCR, rapid antigen test), serology (e.g. ELISA, virus neutralization assay), known or potential risk factors for severe disease (e.g. type 2 diabetes mellitus, hypertension, obesity, smoking, cancer, COPD, chronic kidney disease, cardiovascular disease, immunosuppression), COVID-19 systemic disease, and therapies are important data elements to capture. Neurologic signs and symptoms such as anosmia and dysgeusia are especially critical for clinicopathologic correlation. A literature review of COVID-19 neuropathology papers encompassing 184 patients is used to identify neuropathological features relevant for annotation and include microglial activation, astrogliosis, meningoencephalitis, hypoxic-ischemic change, hemorrhage, microthrombi, Alzheimer Type II astrocytosis, neuronophagy, and demyelination. Brain regions recommended for procurement continue to evolve as a better understanding of Neuro-COVID is achieved, but the medulla, which has demonstrated neuronophagy and microglial nodules, and olfactory bulb, thought to be a portal of entry for the virus, are major considerations for sampling. 84 An ImageJ Toolset for Survival and Cumulative Event Analysis in Longitudinal Live-imaging Experiments Derek Oakley1, Mirra Chung1, Bradley Hyman1, Matthew Frosch1 1Massachusetts General Hospital/Harvard Medical School Single-cell survival analysis is a useful approach for understanding factors that contribute to cell health, particularly in cultured neurons. However, this type of analysis can be difficult to perform due to the relatively large number of data acquisition and analysis steps necessary to produce results. The Single Cell Phenotyping and Survival Analysis toolset provides a simplified approach for survival and cumulative event analysis in cultured cells. Implemented entirely with in NIH ImageJ, the toolset contains a guided methodology to track and phenotype single cells in time lapse imaging experiments and to subsequently produce survival and cumulative event plots as well as montaged images following each tracked cell through time. The output figures produced are comparable to those produced by existing dedicated survival analysis software and include basic statistical comparisons. In addition, several methods for data transformation and migration are included in order to aid in expected analyses. In this work, the Single Cell Phenotyping and Survival Analysis toolset is presented and applied to survival and phenotype tracking in human induced pluripotent stem cell-derived cortical neurons. 85 A Validated Neuroanatomical Segmentation Protocol for the Hippocampal Subfields in Whole-slide Images Esma Karlovich1, Ricardo Insausti2, Gabriel Marx1, Diana Dangoor1, Maggie Krassner1, Marissa Farinas1, Kurt Farrell1, John Crary1 1Icahn School of Medicine at Mount Sinai; 2Universidad de Castilla-La Mancha The hippocampus consists of histologically distinct and functionally specialized subfields that are selectively vulnerable across various neurological and psychiatric diseases, including neurodegenerative diseases, hypoxic-ischemic injury, and epilepsy. Computational approaches utilizing digitized whole-slide images (WSI) are increasingly used to quantify neuropathological features, but neuroanatomical segmentation of the subfields for analysis is challenging on routine stains commonly deployed in neuropathology laboratories. Critically, no validated approach has emerged to clearly delineate the borders of the subfields. The goal of this study was to develop a protocol to reliably and reproducibly define the neuroanatomical boundaries of the hippocampal subfields on WSI to be used for translational pathoanatomical correlative studies. We deployed a series of WSI of formalin-fixed paraffin-embedded sections from the posterior hippocampus from autopsy tissue of individuals with varying degrees of age-related changes and neurodegeneration (n=13) stained with luxol fast blue counterstained hematoxylin & eosin. The team reviewed the literature and stained sections and used key differentiating features to develop a segmentation strategy. Four non-neuroanatomist raters independently annotated the dentate gyrus, CA1, CA2, CA3, and subiculum; then, the segmentations were compared for inter-rater reliability. These annotations were confirmed using expert neuroanatomist annotations and immunohistochemical stains with calbindin, substance P, parvalbumin, and NeuN antibodies, along with cresyl violet counterstained luxol fast blue. We found that this approach is highly reproducible (Dice similarity score > 0.7). In conclusion, this validated protocol is potentially useful for studies addressing the selective vulnerability of the hippocampal subfields to neurodegeneration and other pathologies. 86 The Implementation of a Freezerworks Data Management System into an Extensive Human Brain Bank and Biospecimen Repository Callen Spencer1, Jaclyn Lilek1, Thanapron Athamanah1, Alexis Menias1, Alexander Feldman1, Allegra Kawles1, Grace Minogue1, Tamar Gefen1, Qinwen Mao2, Changiz Geula1, Emily Rogalski1, Robert Vassar1, Marek Mesulam1, Margaret Flanagan1 1Northwestern University; 2University of Utah Banking of human tissue is crucial for furthering biomedical research. To date, there are 120 accredited human tissue banks in the United States. Specifically, the Mesulam Center for Cognitive Neurology and Alzheimer’s Disease banks human brain tissue and related bio-fluid samples, including fixed and frozen brain tissue, paraffin embedded brain tissue, blood, plasma, purified DNA and cerebrospinal fluid samples. Over the span of almost three decades, multiple inventory techniques have been employed at the Mesulam Center by many faculty members and laboratory technicians. In an effort to standardize and streamline the biospecimen sample tracking process, we conducted a comparative analysis of digital barcoding systems and implemented Freezerworks: Ascent Edition. First, a comprehensive inventory of each sample type was completed to establish the specific biospecimen management needs of the bank. Barcoding systems were evaluated on the criteria of cost, digital interface, accessibility, efficiency, and sample capacity, and the Freezerworks system was selected for its cost effectiveness, customization options, and user-friendly interface. The Freezerworks system allows for complete customization of data management and efficiently produces reports of the inventory and transactions. It also tracks samples and aliquot lineage, monitors sample distribution and depletion, and completes simple to complex sample searches pertaining to any and all fields. Implementation of the Freezerworks technology required assigning each individual biospecimen sample with a unique aliquot identifier and subsequently physically labeling all samples with a barcode. Upon completion, our finalized, digitized inventory of the over 10,000 human brain tissue and ancillary samples, will enable a standardized procedure when searching for samples suitable for individual research studies when requested by researchers in addition to tracking remaining amounts of sample per biospecimen type. In conclusion, this biospecimen management inventory technology is beneficial in maintaining banked tissue and biospecimen samples enabling streamlined sample distributions to impactful neurodegenerative research. 87 3D Histopathologic Evaluation for Degenerative White Matter: Cerebral Small Vessel Diseases Rie Saito1, Hiroaki Nozaki2, Kazuki Tainaka3, Masahiro Uemura2, Masahiro Suzuki4, Masaharu Tanaka5, Arika Hasegawa6, Takashi Abe7, Aki Sato8, Hideki Hashidate9, Shuichi Igarashi8, Ryoko Koike6, Osamu Onodera2, Akiyoshi Kakita1 1Department of Pathology, Brain Research Institute, Niigata University; 2Department of Neurology, Brain Research Institute, Niigata University; 3Department of System Pathology for Neurological Disorders, B. R. I., Niigata Univ.; 4Department of Neurology, Mishima Hospital; 5Department of Psychiatry, Mishima Hospital; 6Department of Neurology, NHO Nishiniigata Chuo Hospital; 7Department of Hematology; 8Department of Neurology, Niigata City General Hospital; 9Department of Pathology, Niigata City General Hospital Objective: To clarify the clinicopathologic features of autopsied patients with CADASIL, HTRA1-autosomal dominant disease (HTRA1-AD) and sporadic small vessel disease (sSVD). Methods: From a cohort of 80 consecutive autopsied patients with SVD, we retrieved those with genetically confirmed CADASIL and HTRA1-AD (3 and 3 patients, respectively), and four with sporadic SVD. We examined their clinicopathologic features, and quantitatively evaluated white matter and vascular changes in the frontal portion of the centrum semiovale (CSO) by integrating data obtained from analyses of both conventional 2-dimensional (2D) and chemically cleared 3D tissue. Results: Quantitatively, the white matter pathology, including the density of myelin and axons and the extent of gliosis, was most severe in CADASIL, but unexpectedly sSVD was second in order of severity, followed by HTRA1-AD. The vascular pathology, including arteriole and capillary sclerosis and the extent of the perivascular space, was most severe in CADASIL, whereas the density of smooth muscle actin (SMA) positivity was most decreased in HTRA1-AD. 3D immunohistochemistry for SMA demonstrated two distinct patterns of SMA loss within the vessels distributed in white matter lesions: (1) CADASIL and sSVD: diffuse loss, being particularly prominent in small branches, (2) HTRA1-AD: selective loss in main branches. Conclusion: Extent of white matter and vascular degeneration varies among the types of small vessel disease, and is most severe in CADASIL. These different patterns of SMA loss may be related to the underlying pathomechanisms. 88 Cerebral Amyloidomas Mimicking Vascular Lesions BK Kleinschmidt-DeMasters1, Douglas Ney1 1University of Colorado Health Sciences Center, Aurora, CO Background: Cerebral amyloidomas (CAs) are mass-producing lesions unrelated to cerebral amyloid angiopathy. CAs are congophilic and most commonly due to lambda light chain deposits, contrasting them with light chain deposition disease that has non-polarizable, often kappa light chain aggregates. With the exception of a report of 7 cases with a median follow-up of 21 months, most CAs have been single-case reports with short followup. Neuroimaging features may suggest glioma, although some examples have mimicked granulomatous disease. Objective: To report 2 biopsied CAs which simulated vascular lesions preoperatively and detail unusual histological features plus gross features of a 3rd lesion found at postmortem. Results: 2 woman, ages 56 and 58 years, with right periventricular and right frontoparietal lobe, respectively, lambda light chain CAs were thought to have vascular lesions. Biopsies disclosed amyloidogenic deposits with dystrophic mineralization and multinucleated giant cell reaction, respectively, as well as scant B cells. Case 2 additionally contained one area suspicious for marginal zone B cell lymphoma and had alpha heavy chain amyloid deposition by mass spectometry. Both received low dose (24Gy) cranial irradiation in 12 fractions and have had stable lesions on neuroimaging at 57 and 59 months post biopsy, respectively. A third CA was identified at autopsy as left frontal lobe white matter erythematous, hyperemic discrete lesions; no clinical history was available on this 75-year-old woman. This case contained profuse numbers of plasma cells surrounding the amyloid deposits. Conclusion: These 3 cases illustrate several uncommon neuroimaging, gross, and microscopic features of CAs, as well as provide longer term clinical follow up. 89 The USU Brain Tissue Repository and Neuropathology Core: A Unique Facility in Support of Research on Military TBI David Priemer1, Diego Iacono1, Charles Rhodes2, Daniel Perl3 1Uniformed Services University, Henry M. Jackson Foundation; 2Henry M. Jackson Foundation; 3Uniformed Services University Traumatic brain injury (TBI) is common among military service members and is a major concern of the United States (US) Department of Defense (DoD). Most incidents of military TBI are impact injuries similar to those in civilian populations (motor vehicle accidents, falls, contact sports, etc.). After the 2001 terrorist attacks on the US, approximately 2.6 million US Service Members have deployed to the Middle East where many have been exposed to high explosives (e.g. via improvised explosive devices) by the enemy. While the neuropathologic consequences of impact-TBI are relatively well understood, those of blast-TBI remain unclear, especially long-term consequences. To address this important gap of knowledge, the US DoD, in conjunction with the Uniformed Services University (USU), has established the USU Brain Tissue Repository (BTR), a brain bank that collects, preserves and researches brain specimens derived from deceased active duty and retired service members. The USU BTR currently contains 237 brain specimens, all derived from individuals who served in the military. Many of the donated specimens are from individuals who suffered severe and/or multiple blast exposures while others had careers without battlefield experience. The specimen collection is uniquely young (mean age at death, 47.7 years; range 18-82 years; 58 cases under 40 years). The majority of causes of death represented were sudden, and unrelated to chronic health conditions or prolonged hospitalizations. Using these valuable specimens, we and our collaborators are beginning to identify and characterize the effects of blast-TBI on the human brain. Researchers with an interest in obtaining specimens to support their research may request samples through our web-site: http://www.researchbraininjury.org The opinions expressed herein are those of the authors and are not necessarily representative of the US DoD, USU, the US Army, Navy or Air Force, or the Henry M. Jackson Foundation for the Advancement of Military Medicine. 90 Superficial Siderosis and Beyond: Hemosiderin Deposition in Two Patients with Marfan Syndrome Michael Marshall1, Melissa Krystel-Whittemore1, Sarah Mueller1, Maria Martinez-Lage1 1Massachusetts General Hospital Superficial siderosis (SS) is a rare condition caused by the deposition of hemosiderin within the central nervous system due to chronic subarachnoid hemorrhage. The most common identified etiology is prior trauma or intradural surgery; however, the cause of bleeding is often unknown. Classically, these patients present with sensorineural hearing loss and ataxia. SS has been reported in a patient with Marfan syndrome, an inherited disorder that affects the connective tissue in multiple organs including blood vessels. We describe here two patients, both with Marfan syndrome complicated by aortic dissection requiring multiple surgeries, who were found to have hemosiderin deposition in the brain on post-mortem examination, one with classic SS and the other with a deep distribution of perivascular hemosiderin and mild leptomeningeal cerebellar hemosiderin. Patient 1 was a 47-year-old woman who suffered from altered mental status soon before death, electroencephalographic seizure activity, and a prior episode of lower extremity weakness with features of spinal dural ectasia on imaging. Prominent yellow-orange discoloration along the pial surface of the posterior fossa and cervicothoracic cord was grossly seen at autopsy. On histologic examination, beyond these areas, there was significant hemosiderin deposition in the central portion of both optic nerves and in the frontal cortex. Patient 2 was a 43-year-old man, with a history of paraplegia resulting from anterior spinal artery syndrome, who presented with cardiac arrest. Neuropathological examination revealed moderate diffuse perivascular hemosiderin deposition with a predominant white matter distribution, with mild leptomeningeal hemosiderin in the cerebellum. As a result of prior aortic dissection, both patients were chronically anticoagulated, which may have been a contributing factor in the development of siderosis. These two cases add to the possibility of Marfan syndrome being a risk factor for developing SS. 91 Multilobar Focal Cortical Dysplasia Type IIA in a Child Presenting with Febrile Infection-Related Epilepsy Syndrome (FIRES) Colin Kanach1, Nupur Lala2, Ivana Delalle2, Mayra Montalvo2, Sarah Welsh2, William Brown2, Luca Bartolini2, Rachit Patil2 1Rhode Island Hospital/Brown University; 2Brown University FIRES is a new onset refractory status epilepticus preceded by febrile infection starting between 2 weeks and 24 hours prior to onset of seizures. Outcomes include catastrophic epilepsies with significant morbidity and mortality in children. The pathogenesis of FIRES is not understood due, in part, to the paucity of brain tissue available for histopathologic analysis. Here we describe clinical and autopsy findings in a child with a new onset and prolonged refractory status epilepticus preceded by infection. A 7-year-old girl with normal development and type 1 diabetes presented with seizure and encephalopathy following fever and sore throat for 1 week, resulting in altered mental status and respiratory failure requiring intubation. Seizures arising in the right occipital region were noted, with progression to refractory status epilepticus. Autoimmune work up was unremarkable. MRI brain showed subtle hyperintensity in bilateral occipital lobes that may be linked to seizure activity. On Day 12, the decision for compassionate extubation was pursued. Postmortem neuropathology exam was performed. Neuropathological examination revealed a developmentally normal brain for age weighing 1,228 g. Findings included mild cytoarchitectural abnormalities comprised of laminar disruptions, microcolumns, and microfoci devoid of cortical neurons. These findings were evident within the left prefrontal, bilateral parietal, and the right parieto-occipital cortexes. Immunohistochemical stains for SMI-31 showed positive neurons within the left subiculum of the hippocampus, left occipital, bilateral parietal, and the right parieto-occipital lobes. Additionally, an inflammatory infiltrate comprised of predominately CD3+ was present within the deep gray matter of the brain, along with focal subpial gliosis. Post-mortem examination of the brain revealed changes consistent with FCD type IIa in cortical regions harboring epileptogenic foci on EEG. The co-occurrence of FIRES and FCD within areas of seizure activity, raises the possibility that FIRES syndrome may be related to post-infectious seizures arising in seizure-prone areas of the brain. 92 Two Patients with Temporal Lobe Sclerosis and a History of Seizure in Early Childhood Masashi Mizutani1, Suguru Yokosako2, Naoki Ikegaya3, Taiju Hayashi4, Yukio Kimura2, Terunori Sano1, Akihiko Ishiyama4, Noriko Sato5, Masayuki Sasaki4, Masaki Iwasaki2, Masaki Takao1 1National Center of Neurology and Psychiatry, Laboratory Medicine; 2National Center of Neurology and Psychiatry, Department of Neurosurgery; 3Department of Neurosurgery, Yokohama City University School of Medicine; 4National Center of Neurology and Psychiatry, Department of Pediatrics; 5National Center of Neurology and Psychiatry, Department of Radiology; 6National Center of Neurology and Psychiatry, Department of Pediatrics Temporal lobe sclerosis (TLS) is considered part of the spectrum of mesial temporal sclerosis. Neuropathologic characteristics of TLS include loss of neurons in layers II/III and gliosis with hippocampal sclerosis. Clinically, TLS is characterized by a history of febrile seizure. We present two patients with TLS who experienced febrile seizure in early childhood and were successfully treated with epilepsy surgery. Case 1: A 43-year-old woman presented with drug-resistant focal impaired awareness seizures since age 8 years. She had a febrile seizure at age 3. T2-weighted magnetic resonance imaging (MRI) showed atrophy and increased signal intensity in the right hippocampus and temporal pole. Neuropathologic analysis of the resected specimen showed focal cortical dysplasia type IIIa with hippocampal and temporal lobe sclerosis characterized by neuronal loss and gliosis in cortical layers II/III. The patient’s seizure frequency decreased after surgery. Case 2: An 11-year-old girl presented with tonic seizures since age 4 years. At age 11 months, she had an episode of acute encephalopathy with biphasic seizures. T2-weighted MRI showed atrophy and increased signal intensity in the left hippocampus and temporal pole. Neuropathologic analysis of the resected specimen showed focal cortical dysplasia type IIIa and dispersion of granule cells in the dentate gyrus. The patient’s seizures ceased after surgery. Both patients had precipitating insult in early childhood and pathologic findings consistent with TLS. TLS may represent a neuropathologic phenotype of intractable temporal lobe epilepsy. Further studies to clarify the pathologic mechanisms of TLS are warranted. 93 Leigh Disease-Like Neuropathology in an Adult Following Covid-19 Infection and Global Anoxia Raymond Sobel1, Benjamin Dulken1, Richard Reimer1, Christine Louie1 1VA Palo Alto/Stanford University School of Medicine A 72-year-old man with history of hypertension, hyperlipidemia, DM2, smoking, and obesity had Covid-19 two months prior to death (PTD). He recovered symptomatically but was hospitalized briefly 5 weeks PTD for possible bowel ischemia or infection; he tested Covid+ at that time. Two weeks later he presented with abdominal pain and fever. During this hospitalization he suffered an unwitnessed cardiopulmonary arrest. Despite return of systemic circulation he was deeply comatose off sedatives and without metabolic derangements. Head CT scans at 24 hours showed old encephalomalacia and at 10 days showed diffuse cerebral edema and anoxic brain injury. On transfer to the VA, he remained deeply comatose, with asymmetric fixed pupils, and rhythmic jaw movements. Serum lactate was elevated twice. He died 2 weeks after admission to hospice. Autopsy showed atherosclerotic vascular disease; lungs showed chronic inflammation and interstitial fibrosis. Neuropathologic examination demonstrated old traumatic encephalomalacia and the expected diffuse subacute hypoxic-ischemic injury to cerebral cortex, hippocampi and cerebellum. Additionally, there were bilaterally symmetric circumscribed areas of softening in putamen, globus pallidus, mamillary body, thalami, peri-aqueductal region, substantia nigra, and medulla. These showed sheets of macrophages, microvascular proliferation, hemorrhage, gliosis and demyelination with neuron preservation; some were necrotic. There were extensive CD163+ microglia/macrophages and focally numerous CD3+ T lymphocytes within and adjacent to lesions. There were similar lesions in anterior horns; there were microinfarcts in the anterior pituitary. Bilaterally symmetric subacute necrotizing lesions in deep gray matter, brainstem, and spinal cord are characteristic of Leigh disease (Lake, 2015). Similar findings were reported in a healthy adult following an unexplained collapse (McKelvie, 2012). We hypothesize that our patient may have had an underlying mitochondrial mutation (as in Leigh disease) (Saneto, 2020), or other metabolic process that manifested as a crisis of energy generation triggered by the Covid infection and/or respiratory arrest. 94 Cocaine-induced Multifocal Leukoencephalopathy: A Case Report Ruihe Lin1, Upasana Joneja2, Hamza Shaikh3, Lawrence Kenyon1 1Department of Pathology, Thomas Jefferson University; 2Department of Pathology, Cooper University Health Care; 3Department of Neurointerventional Surgery, Cooper University Health Care Cocaine induced brain injury is often secondary to hypertension resulting in ischemic or hemorrhagic infarction. Cocaine may also rarely cause a vasculitis. An additional rare cause of cocaine induced brain injury is multifocal demyelination. We report a case of a 57-year-old woman with a history of long-term cocaine use who was in her usual state of health the day prior when she was found unresponsive at home. Brain MRI showed restricted diffusion involving bilateral middle white matter tracts throughout the supratentorial brain, indicating toxic leukoencephalopathy. A urine drug screen on admission was positive for cocaine metabolites. She never regained consciousness and eventually died three weeks later secondary to multi-organ failure. Postmortem neuropathological examination identified multiple deep white matter lesions that did not include the corpus callosum or posterior poles of the occipital lobes. Unlike the demyelination described from inhalation of heroin vapor (Chasing the dragon), the brainstem and cerebellum were spared. Similarly, the lack of involvement of the occipital lobe white matter excludes posterior reversible encephalopathy syndrome (PRES). Microscopic examination confirmed widespread multifocal demyelination, consistent with cocaine-induced leukoencephalopathy, very similar to that described in other patients whose only risk factor was recent cocaine use. Improved recognition of this rare consequence of cocaine toxicity will hopefully result in appropriate early treatment, as the condition is not uniformly fatal. In some reported cases, patients have been successfully treated with intravenous methylprednisolone and plasma exchange. 95 Cerebellar Developmental Gene Mutations Co-occurring with PTEN Mutation Result in Lhermitte-Duclos Disease Saman Ahmadian1, Hannes Vogel1 1Stanford University Medical Center Background: Cowden syndrome (CS) is an autosomal dominant disease associated with a germline mutation in PTEN. CS increases the risk for malignancies and hamartomas in multiple organs. It remains unclear as to why certain tumors arise in some patients and in particular locations. Lhermitte-Duclos disease (LDD) or dysplastic gangliocytoma of the cerebellum is a hamartomatous tumor often associated with CS. We report NGS results in three LDD patient cases and propose a novel explanation for their occurrence. Design: Patients undergoing resection in LDD were studied using Stanford's Solid Tumor Actionable Mutation Panel (STAMP). Results: Case 1: 43-year-old female with CS having multiple trichilemmomas, hypothyroidism, breast cancer, and megacolon. Histologic sections confirmed the LDD diagnosis. NGS indicated PTEN, NF1, EPHA2, and PPP2R1A mutations. Case 2: 46-year-old female with SLE and thyroid disease and headaches. NGS indicated PTEN, FGFR3, and GATA3 mutations. Case 3: 62-year-old female with benign thyroid nodules and headaches. NGS indicated PTEN and FBXW7 mutations. VUS mutations were also identified in ERBB2, GATA3, MDM4, and MYC. Conclusion: Among the multiple mutations found through NGS testing, each case has at least one mutation affecting cerebellar development in addition to PTEN mutations. NF-1, mutated in Case 1 acts on proliferation and migration of granular neuron progenitors. FGFR3, mutated in Case 2 affects the differentiation of Bergman glia and deep cerebellar nuclei during early postnatal development of the cerebellum. The third patient has a mutation in FBXW7 that controls neural stem cell differentiation and apoptosis during cerebellar development. PTEN mutation is the critical genetic factor in Cowden Syndrome; the presence of a second mutation involved in cerebellar development for these three cases appears to be the predisposing factor for LDD. This “two-hit” sequence involving germline mutation and superimposed presumed somatic mutation is the first report to possibly explain organ-specific tumorigenesis in CS. 96 Histologic and Clinical Features of Nasal Glioneuronal Heterotopia (Nasal Glioma) Ahmed Gilani1 1University of Colorado Anschutz Medical Campus, Department of Pathology Nasal Glioneuronal heterotopia (NGH), also referred to as nasal glioma, is a rare lesion encountered in the nasal soft tissue. NGH likely represents a congenital or developmental abnormality rather than a true neoplasm. However few studied have systematically reviewed the histologic and clinical characteristics of these lesions. We reviewed our experience with this entity reviewing 6 cases encountered at our Childrens hospital over the past 20 years. Unlike encephalocele, none of the NGH cases showed any intracranial extension on MRI. Location of the lesion varied from sub-centimeter subcutaneous mass on the nose in 3 cases (1 on nasal apex, 2 on nasal bridge) to 3 cases with nasal cavity masses. 3 cases presented within the first week of life and the other 3 at 4, 7 and 8 months. Resection was curative with only a single case showing local recurrence. Histologic evaluation revealed prominent gemistocytic astrocytes surrounded by GFAP+ glial fibers. Prominent fibrosis and collagenization separating glial tissue into nests were seen in 3/6 cases. Synaptophysin was focal and faint. A minority of cases showed NeuN+ neurons. Proliferative activity was low with absent mitoses and MIB-1 positivity of less than 2%. Multinucleation and absence or scarcity of neurons also distinguished NGH from encephlaocele, a leading clinical consideration in many cases. Disorganized leptomeningeal tissue was found in 2 cases. BRAFV600E stain was negative in all cases. In conclusion, we highlight the unique radiologic and histologic features of nasal glioneuronal heterotopia which distinguish these lesions from glial/ glioneuronal neoplasms on the one hand and encephalcoele on the other. PLATFORM 5: Neurodegenerative Disease 2 97 Age-related Progression of Alzheimer Disease Neuropathologic Change (ADNC) in Cognitively Normal Individuals Jamie Walker1, Shiva Kazempour1, Jeff Schaffert2, William Goette2, Timothy Richardson1, Charles White2, Habil Zare1 1UT Health San Antonio; 2UT Southwestern The strongest risk factor for the development of Alzheimer disease neuropathologic change (ADNC) and the associated cognitive decline is age. Herein we demonstrate the age-related progression of ADNC in all individuals (cognitively impaired and normal, n = 4,659) as well as in only cognitively normal individuals (CDR = 0, n = 542). With formulated plots generated from these data, we aim to establish standard lines or curves (similar to a growth chart) that may be utilized to measure the extent to which an individual’s AD pathology varies from the estimated normal range of pathology in cognitively normal individuals. Braak et al. previously demonstrated the progression of Braak stage and Thal phase with age. However, cognitive status was not included in that particular study. We have replicated the findings from the Braak study with our analysis of individuals at all cognitive levels and have developed separate graphs for cognitively normal individuals. Interestingly, we found that although Braak stage and Thal phase progressively increase with age in normal controls, the CERAD neuritic plaque (NP) score and ADNC remain at low levels in cognitively normal individuals. This suggests that an increasing burden of neuritic plaques is a strong predictor of cognitive decline. Whereas, neurofibrillary degeneration and β-amyloid (diffuse) plaque deposition, both to some degree, are normal pathologic changes of aging that occur in all individuals regardless of cognitive status. Furthermore, with linear models, we are able to identify deviations from normal such that we can define the amount of neuropathologic change in cognitively normal individuals that would qualify them to be “resilient” against the pathology (significantly above the normative values) or “resistant” to the development of pathology (significantly below the normative values). 98 Caspase-6 Truncated Tau Play A Major Role In Alzheimer's Disease: Diagnostic And Therapeutic Implications Panos Theofilas1, Antonia Piergies1, Petersen Cathrine1, Chao Wang2, David Butler3, Song Hua Li1, Brian Chin4, Teddy Yang4, Shireen Khan5, Ramond Ng5, Salvatore Spina1, William Seeley1, Bruce Miller1, Li Gan6, Jason Gestwicki1, Celeste Karch7, Sally Temple3, Michelle Arlin1, Lea Tenenholz Grinberg1 1UCSF; 2Gladstone Institute of Neurological Disease; 3Neural Stem Cell Institute, Albany, NY; 4Shanghai ChemPartner; 5ChemPartner San Francisco; 6Weill Cornell Medicine; 7Washington University School of Medicine Background: Tau truncation by active caspase-6 facilitates the formation of neurofibrillary tangles. We previously demonstrated that neuronal active caspase-6 co-occurs with phosphorylated (p-tau) tau during the early stages of Alzheimer’s disease (AD). Here, we explored the relationship between caspase-6 activation, caspase-6 cleavage of tau, and the formation of p-tau aggregates in human brains affected by AD and other tauopathies and in iPSC-derived neurons with MAPT V337M mutation and isogenic controls (iNeurons). Method: We developed novel neoepitope antibodies against tau truncated by caspase-6. We performed 5-plex immunofluorescence on tissue microarrays from two neocortical areas and quantified neuronal and glial positivity for active caspase-6, tau truncated at residue D402 (D402) and D13 (D13), and p-tau (Ser202, CP13) and their co-occurrence in AD, AGD, CBD, PiD, PSP, and healthy aging controls. We also characterized the temporal appearance of caspase-truncated and other tau species in iNeurons and interrogated changes in phenotype after treatment with caspase inhibitors Results: Percentages of neurons positive for D402 and D13 were markedly higher in AD, followed by PiD, relative to the 4-repeat tauopathies. Surprisingly, in AD, only ∼44.25% of these neurons showed p-tau positivity. Mutated iNeurons showed a significant higher amount of caspase-truncated tau than controls by 3 months. Treatment with caspase-inhibitors rescued the phenotype of mutated iNeurons. Conclusions: Caspase-6-cleaved tau, which is neurotoxic in experimental models, seems to be a prominent feature of sporadic tauopathies with a 3-repeat tau component. Moreover, time-dependent accumulation of caspase-6 cleaved tau in V337M MAPT neurons promoting neurotoxicity was reversed by caspase inhibition. Altogether, early modulation of caspase-6 activation and truncated-tau levels could represent a promising therapeutic strategy in AD, warranting further development of caspase-6 inhibitors. Caspase-cleaved tau-based biomarkers. Finally, labeling p-tau pathology AD is insufficient to map the extent of AD-tau pathology and identify the most relevant selectively vulnerable neuronal populations. 99 Tau Phosphorylation Sites Differ in Chronic Traumatic Encephalopathy and Alzheimer Disease SpiroAnthony Stathas1, Victor Alvarez1, Weiming Xia1, Raymond Nicks1, Michael Alosco1, Jesse Mez1, Ann McKee1, Thor Stein1 1Boston University School of Medicine Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease which has been associated with exposure to repetitive head impacts (RHI), typically sustained by contact sport athletes. CTE is characterized by accumulation of tau pathology; however, the phosphorylation sites of tau involved in CTE, and the similarities and distinctions from Alzheimer disease (AD), are not well understood. We measured quantitative levels of phosphorylated tau (p-tau) species within the dorsolateral prefrontal cortex from post-mortem brains (n=473) with neither CTE nor AD (controls), CTE, AD, and both CTE and AD. Specifically, we focused on quantifying levels of Thr181 (p-tau181), Ser202 (p-tau202), Thr231 (p-tau231), and Ser396 (p-tau396), as well as amyloid-beta (Aβ) species Aβ1-38, Aβ1-40, and Aβ1-42. Of the four p-tau epitopes, p-tau202 was the most upregulated phosphorylation site in CTE, and the only epitope that was significantly predicted by total years of contact sport participation (p=0.001), a proxy for RHI. Conversely, p-tau396 was the most increased epitope in AD and also was most closely associated with Aβ1-42 levels (p<0.001). The ratio of p-tau202:p-tau396 was significantly increased in CTE and CTE-AD compared to AD, even between early CTE and AD disease stages (p=0.018). Overall, within the frontal cortex, p-tau202 is associated with RHI and CTE, while p-tau396 is more associated with Aβ and AD. These results may aid in the neuropathological discrimination of CTE and AD as well as the development of clinical biomarkers for CTE. 100 Phosphorylated-tau Comparisons in Synaptosomal Fractions from Human Brain Tissue in Alzheimer’s Disease Progression Jaclyn Lilek1, Alexander Feldman2, Kaouther Ajroud2, Sesha Krishamachari3, Tamar Gefen1, Callen Spencer1, Qinwen Mao1, Jessica Tranovich4, Changiz Geula1, Clifford Jack, Jr.5, Robert Vassar1, Marsel Mesulam1, Ross Reichard6, Melissa Murray4, Dennis Dickson4, Robert Petersen7, Michael Koob3, Dezhi Liao8, Michelle Mielke9, Kathyrn Nelson10, Margaret Flanagan1 1Mesulam Center for Cognitive Neurology and Alzheimer’s Disease; 2Department of Pathology, Northwestern University, Chicago, IL; 3Department of Laboratory Medicine and Pathology, University of Minnesota; 4Department of Neuroscience, Mayo Clinic, Jacksonville, FL; 5Department of Radiology, Mayo Clinic, Rochester, MN; 6Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN; 7Department of Neurology, Mayo Clinic, Rochester, MN; 8Department of Neuroscience, University of Minnesota, Minneapolis, MN; 9Department of Health Science Research, Mayo Clinic, Rochester, MN; 10Department of Medicinal Chemistry, University of Minnesota, Minneapolis, MN Introduction: Intracellular inclusions of tau proteins correlate with, and precede, cognitive deficits in neurodegenerative disorders, including Alzheimer’s disease (AD). Molecular mechanisms by which intracellular tau disrupts synaptic function and impairs cognition, however, remain incompletely elucidated. We used a highly sensitive, high throughput single molecule array (SIMOA) assay to quantify phosphorylated (phospho-) and total tau in synaptic fractions and assessed differences stratified by Braak neurofibrillary tangle (NFT) stage. Methods: Frozen tissue was used from entorhinal and middle frontal cortices from 50 age- and sex-matched individuals (Mayo Clinic and Northwestern Alzheimer’s Disease Centers and Mayo Clinic Study of Aging). Inclusion criteria required the full spectrum of AD Neuropathologic Change, while excluding significant co-existing lesions. A fractionation protocol was performed on human brain tissue. Tau was quantified in each separate fraction (S2 – cytosolic, S4 – presynaptic, P4 – postsynaptic) using Quanterix Simoa-HD1 Platform and Quanterix Tau 2.0 and p-Tau231. Western blotting ensured enrichment of proteins in appropriate fractions. Results: Phospho-tau ratios of P4 to S4 fractions were compared, stratified across Braak NFT stages. Spearman’s Rho coefficients were statistically significant in both middle frontal and entorhinal cortices (coefficients: 0.38 and 0.49, respectively). When stratified by Braak NFT stage, the entorhinal cortex showed a statistically significant decrease in the ratio of S4 phospho-tau to total phospho-tau (coefficient: -0.44). The middle frontal cortex, however, showed a statistically significant increase in the ratio of P4 phospho-tau to total phospho-tau (coefficient: 0.40). Conclusions: Phospho-tau shows differences across pre- and post-synaptic fractions when stratified by Braak NFT stage. This appears to be driven by a relative decrease in pre-synaptic phospho-tau (compared to total phospho-tau) in the entorhinal cortex, and a relative increase in post-synaptic phospho-tau (compared to total phospho-tau) in the middle frontal cortex. Further studies are necessary to uncover the underlying mechanisms behind these findings. 101 Pure Nigral Degeneration: An Uncommon Cause of Parkinsonism that Warrants Search for Genetic Determinants Dennis Dickson1 1Mayo Clinic The most common pathologic findings in the substantia nigra in patients presenting with Parkinsonism with or without cognitive impairment are either α-synuclein or tau pathology. In a series of 450 cases in a brain bank for neurodegenerative disorders collected from 2000 to 2020, we characterized the frequency of substantia nigra pathologic changes. Cases with cognitive impairment (n=237) were compared to cases without cognitive impairment (n=213). The frequency of α-synuclein, tau, or other pathology was 91%, 7%, 2% for those with cognitive impairment and 84%, 11% and 5% for those without. Those with cognitive impairment had higher Braak NFT stage, higher Thal amyloid phase and more frequent TDP-43 pathology. There was no difference in the frequency of cerebrovascular pathology. Neither tau nor α-synuclein pathology was detected in 11 cases without cognitive impairment and in 5 cases with cognitive impairment. Of those with cognitive impairment, 3 had cerebrovascular pathology (vascular parkinsonism), one had post-infectious encephalitis and 2 had TDP-43 proteinopathy. Of the 11 without cognitive impairment, 6 have vascular parkinsonism, 1 had hydrocephalus and 1 had spinal posterior column degeneration. Pure nigral degeneration was detected in the remaining three cases. All three cases with pure nigral degeneration had genetic factors that were likely related to their Parkinsonism (LRRK2 p.R1441C, LRRK2 p.V414I and POLG p.E856K). The results suggest that pure nigral degeneration is a rare form of Parkinsonism and when detected, efforts should be made to characterize family history and consider genetic studies. 102 Vacuolar Tauopathy: A Novel Hereditary Tauopathy Nabil Darwich1, Jessica Phan1, Boram Kim1, EunRan Suh1, John Papatriantafyllou2, Lakshmi Changolkar1, Aivi Nguyen1, Caroline O'Rourke1, Zhuohao He1, Silvia Porta1, Garrett Gibbons1, Kelvin Luk1, Sokratis Papageorgiou2, Murray Grossman1, Lauren Massimo1, David Irwin1, Corey McMillan1, Ilya Nasrallah1, Camilo Toro3, Geoffrey Aguirre1, Vivianna Van Deerlin1, Edward Lee1 1University of Pennsylvania; 2University of Athens; 3NIH Undiagnosed Disease Program, National Human Genome Research Institute Genetic forms of frontotemporal lobar degeneration with tau inclusions (FTLD-tau) are rare and generally associated with MAPT mutations. Other dominant genetic causes of FTLD-tau have not been described. We identified multiple kindred with an autosomal dominant pattern of inheritance of behavioral variant of frontotemporal degeneration. Neuropathologic and neuroradiologic studies revealed a novel form of FTLD-tau with neurofibrillary tangles and neuronal vacuolization which we have named vacuolar tauopathy (VT). VT is associated with a p.Asp395Gly mutation in VCP which is distinct from other VCP mutations that are known to be associated with mutlisystem proteinopathy. VCP is a AAA+ ATPase which hydrolyzes ATP in order to segregate proteins from various macromolecular complexes. In silico and in vitro biochemical studies demonstrated that the p.Asp395Gly results in a partial loss of ATPase activity. Moreover, VCP appeared to exhibit disaggregase activity against polyubiquitinated tau. Finally, the p.Asp395Gly mutation inhibits disaggreegase activity in vitro, and is associated with increased tau aggregation in cellular and animal models. These findings suggest that different mutations of the same gene (VCP) can lead to different underlying neuropathologies (tau versus TDP-43) but the same clinical presentation (FTD), a remarkable instance of allelic heterogeneity. These findings also demonstrate that a partial loss of protein homeostasis (proteostasis) can lead to neurodegeneration and raise the possibility that VCP may be a novel target for the treatment of aging-related neurodegenerative diseases. 103 Distribution Of Neurofibrillary Tangle Pathology Mediates Age Related Clinical Heterogeneity In Sporadic Alzheimer Disease Denis Smirnov1, David Salmon1, Douglas Galasko2, Lawrence Hansen3, Steven Edland4, Gabriel Léger1, Guerry Peavy1, Diane Jacobs1, Robert Rissman5, Donald Pizzo3, Annie Hiniker6 1Department of Neurosciences, University of California San Diego; 2Department of Neurosciences, University of San Diego and VA San Diego; 3Department of Pathology, University of California San Diego; 4Department of Neurosciences, Family Medicine, University of California San Diego; 5Department of Neurosciences, University of California San Diego and VA San Diego; 6Department of Pathology, University of California San Diego and VA San Diego Sporadic Alzheimer’s Disease (AD) patients with earlier age of onset are more likely than those with later age of onset to present with atypical clinical and cognitive features. The pathologic basis of these age-related clinical differences is unknown, but they could be related to differences in the distribution of tau-containing neurofibrillary tangles (NFTs) across age of symptom onset. We examined relationships between distribution of NFTs, presence of non-AD co-pathology, and clinical features in a cohort of patients with sporadic autopsy-confirmed severe (NIA-Reagan “high”) AD and age of onset of 51-60 (n=40), 61-70 (n=41), and >70 (n=40) years. Global cognitive measures at baseline did not differ by age of onset, but those with an earlier age of onset were more likely to present with non-memory complaints, exhibit more psychiatric symptoms, and show greater functional impairment. At autopsy, α-synuclein copathology did not differ by age of onset, but both TDP-43 and microvascular pathology were less common in those with earlier onset. Importantly, the burden of NFT pathology in the midfrontal (MF) cortex relative to the hippocampus was greater in cases with earlier onset, driven by an inverse relationship between midfrontal NFT density and age of onset. In contrast, NFT density in the hippocampus was not related to age of onset, but was greater in those with an APOE ε4 allele or concomitant TDP-43 pathology. On detailed neuropsychological evaluation, patients with earlier onset showed greater impairment in executive function and visuospatial abilities, and exhibited faster longitudinal decline than those with later onset. Mediation analyses showed that the MF / Hippocampal tangle ratio, but not the concomitant non-AD pathologies, mediate the effects of age of onset on executive function and its decline. This suggests that greater cortical NFT burden in earlier onset patients may contribute to agerelated differences in the clinical presentation of AD. 104 Pathologic and Genetic Heterogeneity in Limbic-Predominant Age-Related TDP-43 Encephalopathy (LATE) Matthew Cykowski1, Anithachristy Arumanayagam1, Suzanne Powell1, Andreana Rivera1, Erin Abner2, Gustavo Roman1, Peter Nelson2 1Houston Methodist Hospital; 2University of Kentucky Sanders-Brown Center on Aging Limbic-predominant age-related TDP-43 encephalopathy (LATE) is a common pathology of brain aging. The earliest site of LATE neuropathologic change (LATE-NC) is the amygdala region, but the range of pathologic heterogeneity, and its associations with other pathologies and risk genotypes, are areas in need of further investigation. We examined the pathologic spectrum in the amygdala region of 107 autopsied patients (n=55 women, n=52 men) with a median age of 85 years. Pathologic assessments were made blinded to clinical, pathologic, and risk genotype data (ABCC9, TMEM106B, KCNMB2, GRN, and APOE), using H&E, modified Klüver–Barrera, N-terminal TDP-43 (non-phosphorylated) and Phospho(Ser409/410)-TDP (pTDP). TDP-43 proteinopathy was seen in 57% of cases. Common, and sometimes overlapping, patterns included NFT-like (type “Beta”) TDP-43 inclusions in transentorhinal and entorhinal cortex and amygdala, FTLD-like (type “Alpha”) TDP-43 proteinopathy in lamina II of cortex with associated short neurites, and neurites in periventricular/perivascular white matter and in subpial corticomedial amygdala. Less common forms included granular pre-inclusions by N-terminal TDP-43 in cases with a widespread, severe TDP-43 proteinopathy, and oligodendroglial and/or astrocytic TDP-43 pathology. The presence of LATE-NC was associated with older age at death, hippocampal sclerosis, severity of cell loss in entorhinal cortex, prominent fibrillary astrocytosis, and myelin loss in periventricular white matter. LATE-NC was also associated with a TMEM106B risk allele, with the caveat of the small sample size for other genetic association analyses. Among LATE-NC pathologic subtypes, NFT-like TDP-43 inclusions were significantly associated with presence of an APOE risk allele. Granular pre-inclusions by N-terminal TDP-43 were associated with an FTLD-like pattern involving lamina II and comorbid hippocampal sclerosis, and perivascular TDP-43-immunoreactive neurites in white matter were associated with severe venous collagenosis with white matter rarefaction and abundant corpora amylacea. Our findings highlight the heterogeneity of LATE-NC and the need for further refinement of LATE subtypes in larger samples. PLATFORM 6: COVID19 and the CNS 105 Brain Histopathology in Subjects with COVID-19 Disease Thomas Beach1, Dennis Dickson2, Michael Deture2, Jessica Walker1, Richard Arce1, Michael Glass1, Daisy Vargas1, Lucia Sue1, Anthony Intorcia1, Courtney Nelson1, Javon Oliver1, Aryck Russell1, Katsuko Suszczewicz1, Claryssa Borja1, Jaclyn Papa1, Malaya Sahoo3, Haiyu Zhang3, Daniel Solis3, Thomas Montine3, James Zehnder3, Benjamin Pinsky3, Geidy Serrano1 1Banner Sun Health Research Institute; 2Mayo Clinic Florida; 3Stanford University Department of Pathology The coronavirus SARS-CoV-2 (SCV2) causes pandemic COVID-19 disease. To date, although there have been many clinical and autopsy-based reports that describe a broad range of SCV2-associated neurological conditions, it is unclear what fraction of these have been accompanied by unequivocally-related histopathological changes in the brain, and whether these were due to direct viral brain invasion versus indirect effects caused by systemic reactions to critical illness. We autopsied 20 subjects that died of Covid-19 disease. Subjects ranged in age from 38 to 97 (mean 77) with 9 females and 11 males. Four subjects (20%) had SCV2 RNA in one or more brain regions. Two subjects had neuropathology directly attributable to their Covid-19 illness, one with a large acute cerebral infarction several days after symptom onset, and one with hemorrhagic encephalitis; only the latter case was also SCV2-positive in brain tissue. Most of the 18 other subjects had typical age-related neurodegenerative and cerebrovascular disease. Common additional findings were focal b-amyloid precursor protein white matter immunoreactivity and sparse perivascular mononuclear cell cuffing. Careful comparison with neuropathological findings in subjects who did not have SCV2 infection will be critical for determining whether these and other histopathological features are substantially more likely in COVID-19 disease, and whether they represent direct or indirect viral effects. Supported by a COVID-19 Supplement to a National Institute on Aging grant, (3P30AG019610-20S1), to the Arizona Alzheimer’s Disease Core Center 106 Mapping of SARS-CoV-2 Brain Invasion in COVID-19 Disease Geidy Serrano1, Jessica Walkera1, Richard Arce1, Michael Glass1, Daisy Vargas1, Lucia Sue1, Anthony Intorcia1, Courtney Nelson1, Javon Oliver1, Jaclyn Papa1, Aryck Russell1, Katsuko Suszczewicz1, Claryssa Borja1, Malaya Sahoo2, Haiyu Zhang2, Daniel Solis2, Thomas Montine2, James Zehnder2, Benjamin Pinsky2, Dennis Dickson3, Michael Deture3, Thomas Beach1 1Banner Sun Health Research Institute; 2Stanford University Department of Pathology; 3Mayo Clinic, Florida The coronavirus SARS-CoV-2 (SCV2) causes pandemic COVID-19 disease. To date, although there have been many clinical and autopsy-based reports that describe a broad range of SCV2-associated neurological conditions, it is unclear what fraction of these have been due to direct CNS invasion versus indirect effects caused by systemic reactions to critical illness. Still critically lacking is a comprehensive tissue-based survey of the CNS presence and specific neuropathology of SCV2 in humans. We conducted an extensive neuroanatomical survey of RT-PCR-detected SCV2 in 16 brain regions from 20 subjects who died of COVID-19 disease. Targeted areas included those with cranial nerve nuclei, such as the olfactory bulb, medullary dorsal motor nucleus of the vagus nerve and the pontine trigeminal nerve nuclei, as well as areas possibly exposed to hematogenous entry, including the choroid plexus, leptomeninges, median eminence of the hypothalamus and area postrema of the medulla. Subjects ranged in age from 38 to 97 (mean 77) with 9 females and 11 males. Four subjects (20%) had SCV2 RNA in one or more brain regions including the olfactory bulb, amygdala, entorhinal area, temporal and frontal neocortex, dorsal medulla and leptomeninges. Like other human coronaviruses, SCV2 can invade the brain in susceptible patients. Much remains to be understood, including what viral and host factors influence SCV2 brain invasion and whether it is cleared from the brain subsequent to the acute illness. 107 Neuropathological Findings in COVID-19 Kathryn Eschbacher1, Rachel Larsen1, Ann Moyer1, R. Reichard1 1Mayo Clinic Department of Laboratory Medicine and Pathology Reports of neuropathological findings in cases of COVID-19 infection are limited. A wide spectrum of findings have been reported, ranging from minimal hypoxic ischemic changes, brainstem predominant microglial activation, multifocal and territorial acute infarcts, lymphocytic meningitis, perivascular and parenchymal lymphocytic infiltrate, and acute disseminated encephalomyelitis (ADEM)-like appearance. However, it is unclear if these findings are specific to tissue infection with SARS-CoV-2 or if they represent a consequence of a general state of severe illness. Additionally, there has been variable success in the detection of SARS-CoV-2 in central nervous system tissue by various methodologies. We identified 54 patients who died of complications of COVID-19 (n = 42) or had recovered from COVID-19 shortly before death (n = 12) and had autopsies performed at our institution (39 males, 15 females; median age at death 78 years, range: 28 to 95 years). Digital droplet polymerase chain reaction for the detection of SARS-CoV-2 was performed (cases: n = 17; specimens: n = 27) on sections of the brainstem (medulla), deep gray structures (thalamus or basal ganglia), and cortex (frontal). All cases were negative. Histologic examination demonstrated acute to subacute infarcts (non-territory, n = 9), hypoxic ischemic injury (n = 11), fibrin microthrombi (n = 3), subarachnoid hemorrhage (n = 4), and axonal injury (n = 3). Findings of cerebrovascular disease, including remote infarcts (n = 15) small vessel arteriolosclerosis (n = 50), and large vessel atherosclerosis (n = 45) were identified. 34 cases demonstrated findings of neurodegenerative disease. Our findings suggest that the presence of co-morbid cerebrovascular or neurodegenerative disease are common and may obscure more subtle findings reported in COVID-19. 108 Neuropathologic Autopsy Findings in Patients with COVID-19 Samantha Champion1, Anat Stemmer-Rachamimov1, Matthew Frosch1, Maria Martinez-Lage1 1Massachusetts General Hospital COVID-19 emerged in December 2019 and has since affected millions worldwide. Studies reporting neuropathologic findings have shown variable results. We describe findings in patients from our institution. 20 patients with COVID-19 were evaluated at autopsy. Age at death was 21-91 years (average 64); 16 were males and 4 females; 11 were white, 6 Hispanic or Black, 3 of unknown ethnicity. Neuropsychiatric diagnoses included dementia (4/20), schizophrenia (2/20) and bipolar disorder (1/20). Seven patients suffered from acute encephalopathy. Neuropathologic examination showed arteriolosclerosis in most cases (4- mild; 9-moderate; 3- moderate to severe). Nine demonstrated subacute/remote infarctions and/or hemorrhages (three with cerebral amyloid angiopathy). Two showed acute microscopic ischemic lesions. There were petechial hemorrhages in two cases (including in one case with acute ischemic lesions). Periventricular demyelinating lesions of uncertain origin were present in two cases. 12 cases were examined in detail with immunohistochemistry for CD3, CD68, CD163, and in-situ hybridization (ISH) for COVID-19/SARS-CoV-2 in addition to routine LH&E/H&E, and compared with five age-matched control patients who died from pneumonia. Sections of the cerebellum, frontal and temporal lobes were the most involved by an inflammatory infiltrate. Mild-to-moderate perivascular and leptomeningeal CD68/CD163-positive macrophages and activated microglia (white matter predominance) with sparse to moderate CD3-positive T cells were present in all cases. The age-matched controls showed similar degree of inflammatory activation. All cases were negative for negative for SARS-CoV-2 genomic material by ISH. Neuropathological examination of patients who died with COVID-19 showed a limited inflammatory activation in all cases, similar to that seen in age-matched controls who died of pneumonia. Acute microscopic ischemic/hemorrhagic lesions were only present in a small subset of cases (3/20). This supports an indirect systemic inflammatory reaction and/or cytokine response, associated with microvascular injury in some cases, involving the nervous system in cases with systemic COVID-19 viral infection. 109 Neuropathology of COVID-19, Single Institutional Postmortem Case Series at Icahn school of Medicine at Mount Sinai New York Sadhna Ahuja1, Nadeja Tsankova1, John Crary1, Dushyant Purohit1, Melissa Umphlett2, Clare Bryce2, Mary Fowkes2 1Icahn School of Medicine at Mount Sinai New York; 2Mount Sinai Hospital New York COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a global pandemic leading to major mortality and morbidity. Although it mainly affects the respiratory tract, neurological symptoms are often reported as well. We performed neuropathological examination of 40 COVID19 positive postmortem cases across the Mount Sinai Health System between 02/2020 to 05/2020. Formalin fixed paraffin embedded samples from olfactory bulbs, cortex, basal ganglia, and brainstem were processed and stained with hematoxylin and eosin. Mean age of the patients was 66 years (57% male) with mean brain weight of 1223 g. The circle of Willis showed mild-to-moderate arteriosclerosis in 80% of cases. The most notable histological abnormality seen were microinfarcts typically associated with microthombosis in the parenchyma (40% of cases) and occasionally in leptomeningeal vessels (2 cases), highlighted further with CD61 Immunohistochemical stain. Larger acute/subacute infarcts in the MCA and PCA distribution (20% of cases) and older parenchymal infarcts (7.5% of cases) were encountered as well. Additionally, one case demonstrated innumerable punctate hemorrhagic white matter lesions, histologically manifesting as perivascular zones of demyelination with mild focal acute perivenular inflammation and hemorrhagic necrosis, most consistent with acute disseminated encephalomyelitis/acute hemorrhagic leukoencephalitis (ADEM/AHLE). Other non-specific findings included marked redundancy of the parenchymal vessels, and mild perivascular T-cell (CD8>CD4) lymphocytic inflammation. The olfactory bulbs were examined in 62% of cases and revealed minimal-to-mild perivascular T-cell inflammation. Diagnostic evidence for meningoencephalitis was not seen in any of the cases. How SARS-CoV-2 infection leads to neurological symptoms and whether and how the virus gains access to the CNS is not well understood. The two main recognizing hypotheses are based on neurotropism and direct viral invasion into the CNS and indirect mechanisms of CNS injury mediated by SARS-CoV-2-induced cytokine storm. Careful neuropathological studies are essential to disentangle which changes are attributable to SARS-CoV-2. 110 Adult Human Brain Slice Cultures in the Investigation of SARS-CoV-2 CNS Infection Glaucia Almeida1, Niele Mendes2, Marcelo Volpon3, Guilherme Podolsky-Gondim3, Ricardo Oliveira3, Thiago Cunha4, Eurico Arruda5, Adriano Sebolella6, Luciano Neder2 1Department of Biochemistry and Immunology/Virology Research Center, Ribeirao Preto Medical School, USP; 2Department of Patholology and Forensic Medicine, Ribeirao Preto Medical School, USP; 3Division of Neurosurgergy, Department of Surgery and Anatomy, Ribeirao Preto Clinics Hospital, FMRP-USP; 4Dept. of Pharmacology, Ribeirao Preto Medical School, USP; 5Department of Cell and Molecular Biology/Virology Research Center, Ribeirao Preto Medical School, USP; 6Department of Biochemistry and Immunology, Ribeirao Preto Medical School, USP COVID-19, a disease caused by the infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has currently affected more than 100 million people worldwide, and led to more than 2 million of deaths. In addition to respiratory syndrome, neurological symptoms have also been linked to SARS-CoV-2 infection, including anosmia and memory deficits. Relevant discoveries on cellular and molecular mechanisms underlying brain diseases, including CNS infection, rely on the use of powerful experimental models. Animal models have proved to be of remarkable importance, but differences in cellular receptors structure and distribution, among others, limit their application as disease models, and in some cases, impose the use of human brain-derived models. In the present study, taking advantage of the expertise accumulated in a previous work that evaluate the neural infection by the Oropouche virus, we are using brain slice cultures from adult humans to better understand the pathogenesis of SARS-CoV-2 CNS alterations in a preserved tissue context. SARS- CoV-2 is not only capable to infect but also replicates in human mature CNS cells, according to our RT-PCR results and immunolabelling of double-strand-RNA, a marker of RNA viruses’ replication. More interesting, we have found an increase of RNA- expression of pro-inflammatory cytokines, such as IL-6 and IL-8 after SARS-CoV-2 tissue slice infection. Moreover, preliminary analysis on double-immunolabeling revealed that mature neuroepithelial cells such as astrocytes and even neurons in a lesser extent can harbor SARS-Cov-2 virus particles. We are now directing efforts to evaluate possible ultrastructural alterations induced by SARS-CoV-2 infection in adult human brain slices using transmission electron microscopy. Given the uncertainties on both acute and log-lasting neurological consequences of SARS-CoV-2 brain infection, we do believe that the present demonstration of SARS-CoV-2 infection in adult human CNS cells would be of high interest to the neuroscience community. 111 Mechanism of Olfactory Dysfunction in COVID-19 Infection Cheng-Ying Ho2, Mohammad Salimian1, Jennifer Holler2, Allen Burke2, Heather Ames2, Julia Hegert1, Cinthia Drachenberg2 1Orlando Health; 2University of Maryland Background: Olfactory dysfunction is an early and common presentation of COVID-19 infection. Approximately 30-70% of COVID-19 patients have reported some degree of olfactory dysfunction in the course of disease. Although it has been speculated that viral infection of olfactory neurons may be the culprit, the exact mechanism is unknown due to the paucity of in vivo data. Methods: Olfactory bulb and/or olfactory tract tissues were collected from 9 deceased persons with RT-PCR confirmed COVID-19, including 3 cases of pneumonitis, 3 cases of pneumonitis complicated by diffuse alveolar damage, 2 cases of mild infection and one incidental case identified by postmortem testing. Also collected were tissues from 7 control cases. Routine histopathological examination, immunofluorescence (IF) studies and electron microscopy (EM) were performed. The axon and vascular pathology was further evaluated by quantitative analysis. Results: Among the 9 COVID-19 cases, two cases demonstrated striking axonal degeneration and one case demonstrated a marked loss of axons in additional to axonal degeneration. The remaining 6 cases had axonal pathology ranging from subtle changes to moderate severity. All 9 COVID-19 cases were notable for concomitant endothelial injury of the microvasculature. Common patterns of endothelial injury included cytoplasmic swelling, vacuolization, structural damage of mitochondria and subendothelial edema. Cases with severe endothelial injury, showed narrowing of the capillary lumen, increased lysosomes, rupture of plasma membrane and evidence of microhemorrhage. The severity of the axonal pathology appeared to correlate with the vascular pathology, but was unrelated to the severity of the infection. Of note, evidence of SARS-CoV-2 infection was not detected by IF studies or EM. Conclusions: Our observations in olfactory bulb suggest a mechanism akin to vasculitic neuropathy for COVID-19-associated olfactory dysfunction. The striking axonal pathology in some cases indicates that olfactory dysfunction in COVID-19 infection can be severe and permanent. 112 Neuropathology in COVID-19 Autopsy Examinations – A Single Institutional Experience Michelle McDonald1, Meenakshi Bhattacharjee1 1McGovern Medical School at UT Health Science Center at Houston Background: In 2020 we performed autopsies in 40 patients with COVID-19 infection, 17 of which included brain dissection. We herein report the salient gross and microscopic neuropathologic findings in our institutional cohort. Patient characteristics: 8 males and 9 females, age range from 36 to 71 y (mean=57.4, SD=11.37). 10 were Hispanic, 4 white, 2 black, and 1 Asian. Body mass index (BMI) range 20.4 to 48.8 kg/m2, average of 32.2 (SD=7.14). Five were overweight (BMI: 25 to < 30), and nine were obese (BMI ≥ 30). Common comorbidities were hypertension (n= 8, 47%), diabetes mellitus type 2 (n= 7, 41%), cerebrovascular accident (n= 4, 24%), hyperlipidemia (n= 4, 24%), cancer (n= 3, 18%), dementia (n= 2, 12%), chronic obstructive pulmonary disease (n= 2, 12%), and coronary artery disease (n=2, 12%). Other individual comorbidities were variable. All patients were tested for SARS-CoV-2 by nasopharyngeal swab. Hospitalization ranged from 1 to 69 days, average of 26 days (SD=20). 15 patients were ventilated, 11 received dexamethasone, 9 received convalescent plasma, 8 received Remdesivir, and 2 received hydroxychloroquine, and 4 patients received ECMO. Neuropathological findings: Fixed brain weights ranged from 1050 to 1500 g (mean=1300, SD=136.5). 8 patients had cerebral edema, 8 had cerebrovascular atherosclerosis, 5 had herniation, 4 had atrophy with ex-vacuo hydrocephalus, and 3 had hemorrhages. Microscopic: Intravascular fibrin thrombi in small and medium vessels, petechiae, microscopic and larger acute/subacute infarcts, ring and ball hemorrhages and infarcts, and acute hypoxic-ischemic changes were common findings. Chronic changes included: hypertensive vasculopathy, remote large vessel strokes, Alzheimer disease, metabolic gliosis, and other pathologies specific to individual patients. Notably, the olfactory bulbs and tracts showed no pathologic changes. Conclusion: Large and small vessel cerebral infarcts and hemorrhages in patients that would not be expected based upon their age and co-morbidities suggest an underlying vasculopathy or coagulopathy. PLATFORM 7: Glioneuronal and Non-glial Tumors 113 Intracranial Mesenchymal Tumor With FET-CREB Fusion Is Composed Of Two Distinct Epigenetic Subgroups Emily Sloan1, Rohit Gupta2, Christian Koelsche3, Andreas von Deimling3, Jason Chiang4, Javier Villanueva-Meyer2, Sanda Alexandrescu5, Jennifer Eschbacher6, Wesley Wang7, Manuela Mafra8, Nasir Ud Din9, Emily Carr-Boyd10, Michael Watson10, Michael Punsoni11, Angelica Oviedo12, Ahmed Gilani13, Bette Kleinschmidt-DeMasters13, Dylan Coss14, M. Beatriz Lopes14, Corey Raffel2, Alyssa Reddy2, Sabine Mueller2, Biswarathan Ramani2, Sean Ferris2, Julieann Lee2, Jeffrey Hofmann2, Soo-Jin Cho2, Andrew Horvai2, Melike Pekmezci2, Tarik Tihan2, Andrew Bollen2, Fausto Rodriguez15, David Ellison4, Arie Perry2, Susan Chang2, Mitchel Berger2, David Solomon2 1MedStar Georgetown University Hospital; 2University of California San Francisco; 3Heidelberg University Hospital; 4St. Jude Children's Research Hospital; 5Boston Children's Hospital; 6St. Joseph's Hospital and Medical Center; 7The Ohio State University; 8The Portuguese Institute of Oncology; 9Aga Khan University Hospital; 10ADHB LabPlus; 11University of Nebraska Medical Center; 12Burrell College of Osteopathic Medicine; 13University of Colorado Anschutz Medical Campus; 14University of Virginia Health System; 15Johns Hopkins University School of Medicine Background: Intracranial mesenchymal tumors with FET-CREB fusions occur primarily in children and young adults and have been termed intracranial angiomatoid fibrous histiocytoma (AFH) or intracranial myxoid mesenchymal tumor (IMMT). Clinical outcomes are variable, ranging from long-term recurrence-free survival after resection alone to mortality despite radiation and chemotherapy. Here we use DNA methylation array profiling to further study the ontology of these tumors and identify prognostically relevant epigenetic subgroups. Methods: We performed genome-wide DNA methylation array profiling of 20 intracranial mesenchymal tumors with EWSR1-ATF1 (n=8), EWSR1-CREB1 (7), EWSR1-CREM (4), or FUS-CREM (1) fusion. Epigenomic data was correlated with clinicopathologic features and analyzed by unsupervised hierarchical clustering and dimensionality reduction together with epigenomic data from other relevant intracranial and extracranial tumors. Results: These tumors resolved into two distinct epigenetic subgroups that were both divergent from all other analyzed intracranial neoplasms and soft tissue sarcomas, including meningioma, solitary fibrous tumor, Ewing sarcoma, desmoplastic small round cell tumor, extraskeletal myxoid chondrosarcoma, clear cell sarcoma of soft tissue (CCS), and AFH of extracranial soft tissue. The first subgroup (Group A, 16 tumors) clustered nearest to solitary fibrous tumor and extracranial AFH of soft tissue, whereas the second epigenetic subgroup (Group B, 4 tumors) clustered nearest to CCS but lacked expression of melanocytic markers (HMB45, Melan A, or MITF) characteristic of CCS. No significant difference in patient age, sex, tumor location, fusion partner, or histologic features including stromal mucin content was apparent between the two epigenetic subgroups. However, the Group B tumors had inferior progression-free survival relative to the Group A tumors (median 4.5 vs. 49 months, p=0.001). Conclusion: These findings confirm that intracranial AFH and IMMT represent histologic variants of a single tumor type (‘intracranial mesenchymal tumor with FET-CREB fusion’), and that epigenomic evaluation may provide important prognostic subtyping for this unique tumor entity. 114 LPAR1 And Aberrantly Expressed LPAR3 Differentially Promote the Proliferation And Migration of MPNST Cells Shannon Weber1, Steven Carroll1 1Medical University of South Carolina Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive Schwann cell-derived neoplasms that are the most common malignancy and the leading cause of death in patients with neurofibromatosis type 1 (NF1). In a preliminary genome-scale shRNA screen, we found that the gene encoding lysophosphatidic acid (LPA) receptor LPAR3 is essential for MPNST proliferation and/or survival. Consistent with this, LPA promotes the proliferation, migration and survival of non-neoplastic Schwann cells, and LPA induced proliferation and survival is further enhanced in Nf1-/- Schwann cells. This led us to hypothesize that LPA-regulated signaling pathways are a potential therapeutic target in MPNSTs. To test this hypothesis, we examined the expression of the six LPA receptors in MPNSTs, assessed the role that these receptors play in MPNST physiology and examined their ability to activate key neurofibromin regulated Ras signaling cascades. We found that while normal human Schwann cells express LPAR1 and LPAR6, MPNST cells express LPAR1 and LPAR3. Whole exome sequencing of 16 MPNST cell lines and several surgically resected MPNSTs showed no evidence of mutations in any of the LPAR genes. Exogenous LPA promoted MPNST cell proliferation and migration. Knockdown of LPAR1 expression ablated the promigratory effect of LPA, whereas LPAR3 knockdown decreased proliferation. Inhibition of R-Ras signaling with a doxycycline-inducible dominant negative (DN) R-Ras mutant, which inhibits both R-Ras and R-Ras2, blocked the promigratory effect of LPA; curiously, DN R-Ras expression did not affect migration induced by neuregulin-1β, another growth factor that promotes MPNST migration. LPA-induced migration was also inhibited by the ROCK1/2 inhibitor Y27632, which we have shown functions downstream of R-Ras proteins in MPNSTs. We conclude that LPAR1 and aberrantly expressed LPAR3 mediate distinct effects in MPNSTs and that these receptors and the signaling pathways that they regulate are potentially useful therapeutic targets in MPNSTs. 115 Utility of Next Generation Sequencing (NGS) in the Diagnosis and Management of Peripheral Nerve Sheath Tumors Fausto Rodriguez1, Allan Belzberg1, Carol Morris1, Christine Pratilas1, John Gross1, Christian Meyer1, Kathryn Lemberg1, Jaishri Blakeley1, Ming Lin1 1Johns Hopkins University School of Medicine Neoplasms of the peripheral nervous system represent a heterogenous group with a wide spectrum of morphologic features and biologic potential. Although peripheral nerve sheath tumors (PNST) usually develop sporadically in patients lacking a family history of genetic predisposition, they are important components of a variety of genetic syndromes, and pathologic characterization constitute important diagnostic criteria with consequences for clinical follow-up. Comprehensive molecular genetic profiling using high resolution platforms is currently transforming the approach to pathologic diagnosis of disease and cancer, including PNST. We report the findings of clinical targeted NGS testing using an Illumina platform. A total of 23 tumors from 17 patients were studied with a cancer panel covering coding sequence variants in >400 cancer associated genes as well as selected copy number changes. Tumors tested included high grade MPNST (n=16), low grade MPNST (n=1), cellular schwannomas, (n=2), hybrid nerve sheath tumors (n=2), plexiform neurofibroma (n=1) and atypical neurofibromatous tumor of uncertain biologic potential (ANNUBP)(n=1). Syndrome associations included NF1 (n=16), Schwannomatosis (n=2) and sporadic (n=5). Alterations of interest in MPNST involved NF1 (n=15), SUZ12 (n=8), KRAS (n=1), EGFR (n=1), CRBBP (n=1), MYCN amplification (n=1) and CDKN2A/B copy number loss (n=4). A single EED mutation was associated with a MPNST with myogenic differentiation (Triton tumor). SUZ12, TP53 and NF1 mutations were identified in the single low grade MPNST (initially diagnosed as a schwannoma). Testing of two anatomically separate MPNST demonstrated shared driver mutations in only 1 (of 4) patients, suggesting independent primaries rather than clonally related tumors (metastasis) in 3 patients. Testing of a paired ANNUBP precursor and MPNST in one patient demonstrated shared NF1 mutations but no PRC2 (SUZ12, EED) associated alterations. In summary, NGS has potential utility for robust characterization of nerve sheath tumors, and may represent a robust adjunct for diagnosis and clinical management. 116 Using Methylation Profiling to Guide the Repurposing of Chemotherapies Against High-Risk Meningiomas Anh Tran1, Wenxia Wang1, Denise Scholtens1, Jenny Pokorny1, Yufen Wang1, Aneta Baran1, Felix Sahm2, Charles James1, Craig Horbinski1 1Northwestern University; 2University Hospital Heidelberg Meningioma is the most common primary intracranial tumor, with over 30,000 new cases in the U.S. annually. Despite resection and radiotherapy (RT), many of these tumors recur and cause considerable disability or lethality. Even though they exist outside the blood-brain barrier, there is no proven chemotherapeutic option for high-risk meningiomas. Genomic methylation profiling has enhanced tumor classification and prognostication, but has not yet informed new chemotherapeutic strategies, particularly those that might enhance RT. Therefore, we analyzed methylation data from a previously published dataset of 493 meningioma patients by Sahm et al. (Lancet Oncology, 2017), to infer which signaling pathways were most associated with outcome. Our analyses indicated 981 genes for which methylation of mapped CpG sites was found to be consistently associated with clinical outcomes, at FDR-adjusted p<0.05. Next, using Cytoscape/Reactome FI software, we cross-referenced FDA-approved cancer drugs that target signaling pathways associated with those specific genes and their signaling pathways. This approach identified docetaxel among the top candidates against high-risk meningiomas. Docetaxel is an antimicrotubular antineoplastic agent approved to treat breast, lung, prostate, stomach, and head and neck cancers. In vitro, docetaxel caused apoptotic cell death in 17 established and primary patient-derived meningioma lines, representing all 3 WHO tumor grades. IC50s ranged from 0.8nM to 4.4mM, with more cell proliferation correlating with greater sensitivity. Docetaxel at 2µM enhanced double-stranded DNA damage caused by 2Gy RT in vitro, leading to increased cell death compared to either treatment alone. Mice orthotopically engrafted with patient-derived meningiomas survived longer when treated with docetaxel (5mg/kg x 4 doses) and concurrent 7.5Gy RT (median survival 29 days), compared to control (15 days), docetaxel alone (17 days), or RT alone (20 days, P<0.001). These data suggest that a bioinformatics-driven screening of existing chemotherapeutics can be effective in repurposing the most promising agents against aggressive meningiomas. 117 Histologic Features of AT/RT Associated with Long Survival: A Single-institution Retrospective Review Murad Alturkustani1, Jaclyn Biegel1, Ashley Margol2, Alexander Judkins1, Jennifer Cotter1 1Department of Pathology, Children’s Hospital Los Angeles; 2Cancer and Blood Disease Institute, Children’s Hospital Los Angeles Background: Some atypical teratoid/rhabdoid tumors (AT/RT) have longer than usual survival, the basis for which is not well-understood. Additionally, two entities with SMARCB1 loss in the brain (cribriform neuroepithelial tumor (CRINET), and desmoplastic myxoid tumor (DMT) are often associated with better prognosis than AT/RT. Since AT/RT management includes radiation, and in some cases high-dose chemotherapy with stem cell rescue, recognition of such cases with better prognosis could potentially limit treatment-related morbidity. Design: We retrieved cases diagnosed as AT/RT from our pathology archives from 1990-present and associated clinical outcome data. Long survival was defined as >48 months from diagnosis. We reviewed cases, blinded to clinical outcome, for selected morphologic features (primitive neuroepithelial cells, rhabdoid or epithelioid cells, poorly-differentiated epithelial or papillary features, desmoplastic reaction, glial differentiation, and myxoid/myxohyaline background). Results: 12/41 cases had long survival and one case had a near-long survival (40 months, death secondary to immunosuppression; no residual tumor at autopsy). 9/13 long or near-long survival cases occurred in patients with older age at diagnosis (>36 months). No classic CRINET or DMT were identified. Four histological features associated with long or near-long survival included: predominant ependymal and/or choroid plexus differentiation (n=2, possibly representing a solid pattern of CRINET), advanced glial differentiation (n=5), extensive desmoplastic reaction (n=2), and focal myxoid background (n=4). Of these four features, only advanced glial differentiation and focal myxoid background were identified in cases without long survival (1 case each). Conclusion: We identified tumors diagnosed as AT/RT with recurrent histologic features frequently associated with older age at diagnosis and longer survival. These cases demonstrated atypically advanced, divergent and mixed glial differentiation, desmoplastic reaction, and focal myxoid background. Careful attention to the histopathological features of AT/RT may aid in identifying potential outlier cases with a broader spectrum of clinical behavior than typically assumed for these tumors. 118 Meningioma Tumour Infiltrating Lymphocyte Density Differs By Meningioma Type and Predicts Recurrence in Atypical Meningioma Clinton Turner1, Jessica McLay2, Ari Bok1, Maurice Curtis2, Mike Dragunow2 1Auckland City Hospital; 2University of Auckland Background & objective: Tumour infiltrating lymphocyte (TIL) density is prognostic in various solid tumours. Meningiomas have varying degrees of lymphocyte infiltration. However, it is unknown whether TIL density independently predicts recurrence in meningioma. This study sought to determine whether TIL subset density predicts meningioma recurrence. Method: All meningiomas resected at Auckland Hospital 2002 to 2011 were identified from pathology records. Relevant clinical data, including months to recurrence, and tumour co-variables were recorded. Tumours recurrent from prior to 2002, pre-operatively irradiated/embolized, with insufficient remaining tissue or lymphoplasmacyte-rich histology were excluded. Included cases were reviewed and classified according to the 2016 WHO CNS tumour classification. Tissue microarrays (TMAs) were constructed and sections stained for CD3, CD8, CD4, PD1 and FOXP3. Slides were digitized and TIL density quantified using QuPath. Results: The cohort included 508 meningiomas (476 primary meningiomas, 32 recurrences). For primary meningioma the density of TILs was found to differ significantly by histology. Chordoid meningioma (12 cells/mm2) had the lowest CD3 TIL density while psammomatous (145 cells/mm2) had the highest. Other TIL markers also showed significant differences by meningioma type. The density of CD3 and CD8 positive TILs independently predicted recurrence in atypical meningioma on multivariate analysis. A lower CD3 and CD8 TIL density was associated with increased risk of atypical meningioma recurrence (CD3 p=0.001; CD8 p=0.007). TIL density in all recurrent tumours was generally similar to the primary except for FOXP3 where TIL density was increased in previously irradiated recurrences (p=0.023). Conclusion: TIL density differs significantly by meningioma type. A lower density of CD3 and CD8-positive T-cells is associated with increased recurrence risk in atypical meningioma. While generally stable between primary and recurrence for other TIL markers examined, there does appear to be an increase in FOXP3 cell density in recurrent tumours that had been irradiated prior to resection. 119 FGFR1 Internal Tandem Duplication in Histologically Defined Rosette-forming Glioneuronal Tumor Ahmed Gilani1, BK Kleinschmidt-DeMasters2 1University of Colorado and Childrens Hospital Colorado; 2University of Colorado, Departments of Pathology, Neurology and Neurosurgery Next generation sequencing is increasingly being used as aids to histologic diagnosis. Although molecular alterations are reported to be diagnostic for certain tumor entities, diagnostic dilemmas arise in cases with discordant morphologic and molecular findings. We describe such a case in this report. Recent studies have reported that rosette-forming glioneuronal tumors (RGNT) show characteristic epigenetic and genetic signature including mutations in FGFR1 kinase domain with either PIK3CA or PIK3R1 mutation, often with accompanying NF1 or PTPN11 mutations. We evaluated cases of RGNT diagnosed in our institution for genetic alterations on our in-house 500+gene fusion and mutation panel. 4 cases of RGNT were identified in pathology department’s database from Jan 2015 to Jan 2021. 3 cases showed previously reported characteristic genetic alterations including FGFR1 N546K, PIK3CA and NF1. The fourth case from a 9-year-old male with 4th ventricular tumor had characteristic histologic features of RGNT including with well-defined neurocytic rosettes containing synaptophysin-positive neuropil cores, but failed to show the above mentioned hallmark genetic alterations. Instead, this case showed FGFR1 gene internal tandem duplication (ITD). DNA methylation analysis was conducted but was inconclusive due to low DNA content. This case highlights that genetic variations can be occasionally identified in tumors that are otherwise defined by very specific mutations. Such cases emphasize the need for broad fusion and mutation testing for brain tumors, even those characterized by near-definitional genetic findings necessary for integrated histological-molecular diagnosis. 120 PD-L1 and PD-1 Expression in Pediatric Intracranial Germ Cell Tumors Jared Woods1, Hart Lidov1, Keith Ligon1, Sandro Santagata1, Katherine Warren2, Susan Chi2, Kee Yeo2, Sanda Alexandrescu1 1Department of Pathology, Boston Children's Hospital; 2Dana-Farber/Boston Children's Cancer and Blood Disorders Center Background: Intracranial germ cell tumors (GCTs) represent 2-3% of all primary central nervous system (CNS) tumors. The majority are germinomas, which are radiosensitive and have an excellent prognosis. Contrarily, CNS non-germinomatous GCTs (NGGCTs) have less favorable prognosis and require more aggressive treatment. The expression of checkpoint/immune markers in CNS GCTs, particularly NGGCTs, is unknown. We previously reported a case of a patient whose intracranial NGGCT (predominantly choriocarcinoma) responded to checkpoint inhibition therapy. This case led us to evaluate our archive of intracranial GCTs for expression of PD-L1 and PD-1. Methods: With IRB approval, we searched the pathology archives at our institution for CNS GCTs. Demographic, radiologic, clinical and histologic information was extracted from the medical records. Immunohistochemistry for lymphocytic markers (CD4, CD8, CD20), PD-1, and PD-L1 was performed. PD-L1 was considered positive if greater than 1% and PD-1 was reported as a percentage of positive inflammatory cells. Results: 51 cases were identified, including 28 germinomas (mean age at diagnosis: 15.5 years; 17 males, 11 females), and 23 NGGCTs (mean age at diagnosis: 12.7 years, 22 males, 1 female). Germinomas were mostly suprasellar (17/28) and NGGCTs were predominantly pineal (18/23). 22 germinomas (79%) were positive for PD-L1 expression, and 13 NGGCTs (57%) were positive for PD-L1. Cases of choriocarcinoma showed the most diffuse PD-L1 expression. PD-1 expression was seen in lymphocytes among 27/28 of the germinomas and 20/23 of the NGGCTs (ranging from 1-40% of lymphocytes). As expected, larger quantities of inflammatory cells were present in cases of germinoma. Conclusions: We demonstrate immune activity in CNS GCTs, and our results suggest that immune checkpoint inhibitors may be efficacious in the treatment of intracranial GCTs. Among NGGCTs, cases of choriocarcinoma showed the highest expression in tumor cells, suggesting that this subtype may have the greatest benefit from checkpoint blockade. PLATFORM 8: Trauma and Forensics 121 Visualizing Vascular Proliferation in CTE by Tissue Clearing and Confocal Microscopy Grace Rosen1, Daniel Kirsch2, Sarah Horowitz1, Jonathan Cherry3, Raymond Nicks4, Hunter Kelley4, Rebecca Mathias4, Kerry Cormier5, Caroline Kubilus5, Thor Stein2, Victor Alvarez6, Ann McKee2, Bertrand Huber6 1VA Boston Healthcare System, U.S. Department of Veterans Affairs; 2Department of Pathology and Laboratory Medicine, Boston University; 3Department of Neurology and Laboratory Medicine, Boston University; 4Boston University Alzheimer's Disease and CTE Center; 5Department of Veterans Affairs Medical Center, Bedford, MA; 6Department of Neurology and Laboratory Medicine, Boston University Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease linked to exposure to repetitive head impacts (RHI). The diagnostic lesion for CTE is hyperphosphorylated tau protein (p-tau) in perivascular neurons with or without astrocytes at cortical sulcal depths. Simulations of impacts experienced by athletes suggest that shear stress and deformation of the brain is greatest at sulcal depths. We hypothesize that RHI damages the brain parenchyma leading to neuroinflammation and neoangiogenesis, new blood vessel formation from pre-existing vasculature. Exposure to cumulative RHI, without intervening repair time, may cause chronic inflammation and dysregulated neoangiogenesis. To investigate vascular proliferation in the context of RHI and CTE, we examined 200 µm-thick sections of post-mortem human dorsolateral frontal cortex from the VA-BU-CLF (UNITE) Brain Bank. Study participants included those with neuropathologically diagnosed CTE (n=15 severe, n=15 mild), RHI exposure without CTE (n=15), and RHI-naïve controls (n=10). Tissue was post-fixed via SHIELD, optically cleared, and stained with fluorescently-labeled tomato lectin to visualize vasculature. Clearing allowed imaging of the full 200 µm-thick section, sufficient for observation of vessel branching. We quantitated variables including vessel branch density and fractional volume to measure potential evidence of angiogenesis. In the grey matter at sulcal depths, branch density and fractional volume were significantly increased in CTE cases compared to RHI-exposed cases without CTE. Branch density in the grey matter sulcus correlated positively with the area of p-tau staining determined histologically. These observations are consistent with the concept that in CTE, brain regions more vulnerable to shear stress have increased vascularity and suggest that increased angiogenesis in regions of high p-tau burden may be a CTE feature. The tissue-clearing approach represents a generally applicable protocol by which structures in fixed human tissue can be visualized in thicker sections than with routine histology, allowing for evaluation of morphological features with three-dimensional rendering. 122 Histopathological Findings in the Central Auditory Pathway of Patients with Chronic Traumatic Encephalopathy Renata Knoll1, Raymond Nicks2, Sarah Svirksy2, Aaron Remenschneider1, David Jung1, Victor Alvarez2, Elliott Kozin1 1Department of Otolaryngology, Massachusetts Eye and Ear, Boston, MA; 2Department of Veterans Affairs Medical Center/Boston University Introduction: Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repeated exposure to concussive head trauma. Auditory symptoms have been anecdotally associated with CTE; however, the precise pathophysiology remains unknown. Herein, we aim to investigate if neuropathological changes occur along the central auditory pathway (CAP) in postmortem patients with confirmed diagnosis of CTE. Study design: Histopathological study. Methods: Specimens were obtained from Boston University Brain Bank. A total of 19 brains from patients with a confirmed neuropathological diagnosis of CTE (ten early stage and nine late stage) were evaluated by light microscopy. Twelve additional brains from cognitively intact individuals without history of mild repetitive head injury were used as controls. Specimens were immunohistochemically assessed for presence and quantification of hyperphosphorylated tau (p-tau) density and/or neurofibrillary tangles (NFTs) in the auditory cortex and inferior colliculus (IC). Results: Neuropathological changes were found along the CAP in patients with CTE. NFT density in the gray matter of the auditory cortex and Heschl gyrus was greater in patients with CTE than controls (p<.001 and p<.001, respectively). Late stage CTE patients presented the greatest NFT density in the IC, with a significant difference compared to early stage patients (p=.010). There was a significant positive correlation between NFT density and stage of CTE in the gray matter of the auditory cortex and Heschl gyrus (r= .808, p= < .001 and r= .741, p< .001, respectively. No correlations were found in the IC. Conclusion: This is the first histopathological study to examine the CAP in individuals with CTE. Neuropathological changes in the CAP were found in patients with CTE and are positively associated with increasing CTE stage severity. Further studies are warranted with a larger number of specimens to better characterize neuropathologic change at each stage. 123 Elevated Pathological Tau Accumulation in Chronic Brain Contusion Meagan Chambers1, Jeanelle Ariza1, Trevor Sytsma1, Amanda Keen1, Kim Howard1, Caitlin Latimer1, C Dirk Keene1, Amber Nolan1 1University of Washington Traumatic brain injury is a risk factor for neurodegenerative disease, but the mechanisms are uncertain. Furthermore, how localized injury may influence the connectivity of brain networks and alter trajectories of pathologic peptide aggregation in neurodegenerative disease has never been systematically evaluated. Towards this end, we sought to first evaluate if hyperphosphorylated tau (p-tau) deposition is modified in brain parenchyma adjacent to chronic contusion. In the University of Washington Brain Repository, we searched for cases with a diagnosis of chronic contusion and evaluated p-tau in a section including the contusion, and in a section from the contralateral lobe without contusion (internal control). Cases were excluded if significant p-tau deposition was not identified. A total of nine cases were assessed for neurofibrillary tangles (NFTs), percent area of p-tau staining in the grey matter, and astrocytic tau pathology. NFTs were significantly higher in sections with contusion compared to the internal control (paired t-test, p=0.0375); only 1/9 cases demonstrated a decrease in NFTs in the contusion. Interestingly, this case had a notable history of repetitive head injury including semi-professional rugby, while the other cases appeared to have isolated injuries. A trend was also found for increased deposition with analysis of the ratio of % area for p-tau staining in contusion/control (Wilcoxon signed-rank test, p=0.0742). If the case of repetitive head injury was excluded, this relationship became significant (p=0.0391). Finally, astrocytic tau deposition was frequent in 6/9 cases with predominately white matter and subpial thorn-shaped astrocytes observed. In three cases, astrocytic deposition was only present in the contusional section, while the other three had deposition in both sections. Of note, the pathognomonic lesion of chronic traumatic encephalopathy was not identified in these sections. Although this is a limited case series with heterogenous pathology, the differential p-tau deposition supports a role for TBI-related modulation of neurodegeneration. 124 Beaded Astrocyte Process Dystrophy at Interfaces: An Indicator of Astrocytic Dysfunction or Injury Following Blast Exposure? David Priemer1, Daniel Perl2 1Uniformed Services University, Henry M. Jackson Foundation; 2Uniformed Services University Alterations in astrocytic morphology in neuropathologic disease, particularly outside of neurodegenerative disease, are under-characterized. We examined the brain of a 44 year-old former Navy SEAL with extensive blast exposure history. GFAP immunohistochemistry showed dystrophic astrocytes with a markedly increased density of GFAP-positive, outwardly radiating processes which themselves had numerous small, bead-like expansions. These were predominantly in deep neocortical layers, abutting the grey-to-white matter junction, but also subpial. We subsequently reviewed our electronically scanned slide database, blind to decedent histories, for brains showing similar astrocytic changes, yielding five additional cases. The cohort, composed of male active or former servicemen, averaged 48 years-old (range: 35-82, median: 44). Five of the six total cases had known or inferred blast exposure history. In all cases, beaded astrocyte process dystrophy (BAPD) involved the deep cortex/grey-to-white matter junction, and occasionally cortical perivascular spaces and subpial regions. The frontal and temporal neocortices were involved in all cases, and likewise were always the most severely affected regions. All cases also involved the cingulate cortex. More disseminated cases showed BAPD within the neocortex of the remaining lobes (N=2), entorhinal cortex (N=5), subiculum and CA1 region of the hippocampus (N=2), insula (N=2), caudate nucleus (N=2), and anterior putamen (N=1), but less prominently. Astrocytes elsewhere (e.g. subcortical white matter) appeared normal. Any background neuropathology did not correlate with the distribution/topography of BAPD, with exception of two cases with interface astroglial scarring, a finding associated with blast exposure. We therefore propose that BAPD at interfaces may indicate astrocytic dysfunction/injury following blast exposure. Whether BAPD occurs in other neuropathologies warrants further investigation. The opinions expressed herein are those of the authors and are not necessarily representative of the Department of Defense, Uniformed Services University, the US Army, Navy or Air Force, or the Henry M. Jackson Foundation for the Advancement of Military Medicine. 125 Epilepsy Associated Death in Southwestern Ontario: A Clinical and Pathological Correlation Study Jane Ding1, Ana Suller-Marti2, Peter Liu3, Chelsey Zhao3, Lee-Cyn Ang3, Qi Zhang3 1Schulich School of Medicine and Dentistry, London, Canada; 2Department of Clinical Neurological Sciences, London Health Sciences Centre; 3Department of Pathology and Laboratory Medicine, London Health Sciences Centre Sudden unexpected death in epilepsy (SUDEP) is one of the leading causes of death in epilepsy patients. However, the mechanisms underlying SUDEP remain poorly understood, and there currently exist no neuropathological markers diagnostic of SUDEP. The first objective of this study is to provide a better understanding of the characteristics of SUDEP by comparing clinical and pathological features of epilepsy patients who died of SUDEP and of other causes (e.g. drowning). Seizure activity in the amygdala is thought to play a role in the pathogenesis of SUDEP, and our second objective was to provide a quantitative comparison of the functional neuronal populations of the amygdala in SUDEP and non-SUDEP cases using immunohistochemistry. We identified 152 autopsy cases with history of epilepsy at London Health Sciences Centre from 2000 - 2018. Data was collected from the autopsy report, Neuropathology report, and patient’s medical record. Eighty-nine of the cases were classified as SUDEP based on the criteria outlined by Nashef et. al, 2012. Nineteen paraffinized amygdala sections were obtained from 13 individual SUDEP cases, and 10 sections from 7 non-SUDEP cases. Amygdala sections were stained with Calbindin and Calretinin antibodies to demarcate specific GABAergic interneuron populations, and stains were quantified in QuPath. The findings of this study support what is currently known of clinical characteristics and neuropathological findings in SUDEP. Immunohistochemical analysis reveals an increase in the Calbindin-expressing interneuron population within the lateral, basolateral, and basomedial amygdala of epileptic patients who experienced SUDEP compared to patients who did not. Overall, our study builds upon the knowledge of SUDEP findings worldwide. The immunohistochemical findings suggest that changes in interneuron populations and in the regulation of activity in the amygdala may underly a predisposition to SUDEP in epileptic patients. Finally, our study is of the first to describe SUDEP cases in a Canadian population. 126 Neuropathologic Substrate in Decedents with Cerebral Palsy in a Forensic Setting Sarah Thomas1, Michelle Stram1, Rebecca Folkerth1 1New York City Office of Chief Medical Examiner Clinically, cerebral palsy (CP) encompasses permanent non-progressive movement and posture disorders following presumed in utero or perinatal hypoxia-ischemia (HI). Sometimes the moniker is misapplied due to inaccurate clinical impression of the underlying cause, limited history from caregivers, and/or the need for family support services. Deaths labeled as CP occur in family, group or nursing homes, sometimes with concerns for abuse or neglect, and thus come to forensic attention. Determining an etiologically specific cause of death requires neuropathologic (NP) consultation, including medical record review. We hypothesized that the CP label is inaccurate in a subset of such cases. To determine the actual NP substrate in decedents designated as having CP, we reviewed our records over a 7-year period. Forty-one (41) cases ranged in age from 1 month to 68 years; 29 were male; 21(51.2%) had a history of seizures. Gross and microscopic NP features allowed categorization into 5 groups. Category A (n=26;63.4%) included cases of true perinatal HI (e.g., old periventricular leukomalacia, status marmoratus, porencephaly). Category B (n=1;2.4%) comprised post-neonatal asphyxia. Post-infectious sequelae (e.g., meningitis) were placed into Category C (n=2;4.9%). Category D included non-HI congenital, genetic, developmental, or metabolic disorders(n=10;24.4%);of these, 6 had disorders, such as neuronal ceroid lipofuscinosis, that were solely diagnosed postmortem. Category X (n=2) was applied to those for which no NP substrate for CP/developmental delay was ascertained. 10 decedents (24.4% of the cohort) had NP features described in epilepsy (e.g., hippocampal sclerosis, dentate gyral abnormalities). We conclude that, while about half of cases designated as CP by family or caregivers did in fact have NP evidence of perinatal HI, over a quarter had non-ischemic congenital disorders, including those of heredofamilial origin, of importance to the health of the next of kin. Epilepsy incidence was relatively high among our cohort. 127 Forensic Teleneuropathology: A Remote Viewing Approach for Neuropathologic Consultation in the Forensic Setting Julian Samuel1, Benjamin Criss1, Sarah Thomas1, Naeem Ullah1, Christopher Rainwater1, Jason Graham1, Rebecca Folkerth1, Michelle Stram1 1Office of Chief Medical Examiner, City of New York Access to neuropathologists (NPs) in the forensic pathology (FP) setting varies widely and can affect diagnostic adequacy as well as turn-around time. However, telepathology, as used for frozen section analysis in centers without NP faculty, can be adapted for remote viewing of brain gross examinations (“brain cuttings”), using free software and equipment common to many FP offices, allowing real-time input from an off-site NP. A motorized photography copy stand with adjustable lights was fitted with a digital Canon EOS-80D camera with a fixed focal length lens (fitted with an AC adapter for continuous usage) attached via USB to a computer running Microsoft Teams (MT). The free Canon web utility (EOS 3.13.10) was run in the remote shooting mode providing a real-time display of the camera feed with options for 1x, 5x, and 10x digital zoom, manual and automatic focusing, adjustable exposure, and remote still image capture. The MT application broadcasted the “virtual brain cuttings” via the share screen function. The FP/NP fellows placed case specimens on the stand and livestreamed images to the NP’s remote computer via MT. After discussion of case history and differential diagnosis, specimen(s) were dissected according to standard protocols, with slabs again livestreamed to the NP. When desired, the off-site FP could also remotely participate in the consultation. Between 9/1/20 and 1/31/21, 165 cases were evaluated via teleneuropathology. We found the image resolution to be of high quality, allowing the NP to easily detect and point out subtle findings and make critical decisions on a case-by-case basis, including selection of histologic samples. When the FP participated, real-time discussions of specific diagnostic concerns enhanced the overall consultation. We conclude that teleneuropathology can be adapted to FP offices, using technological infrastructure that may already be available, providing a high-quality mechanism for integrating consistent access to an offsite NP. 128 Julius Hallervorden’s First Neuropathologic Description of the Dementia Pugilistica in a Boxer and his Dark Past David Priemer1, Daniel Perl2 1Uniformed Services University, Henry M. Jackson Foundation; 2Uniformed Services University The first neuropathologic description of a case of dementia pugilistica in a boxer appears in an often-cited but obscure 1954 publication, written in German, entitled Dementia pugilistica mit anatomischem Befund [Dementia Pugilistica with Anatomic Findings] by Brandenberg and Hallervorden. Through the National Library of Medicine, we obtained the manuscript along with high-quality published figures. Following translation of the text and review of the figures, the case does not satisfy current diagnostic criteria for chronic traumatic encephalopathy (CTE), but appears to be an example of early-onset Alzheimer’s disease. Julius Hallervorden was a prominent German neuropathologist who, during the Nazi regime, admitted to receiving almost 700 brains from victims of involuntary euthanasia, including from the ‘Aktion T4’ program, in a collaboration he initiated and was actively affiliated. Victims included patients with intellectual disabilities, malformations, early infantile and/or hereditary disease, and other afflictions. After the war, Hallervorden was interrogated by the Office of the Chief of War Crimes at Nuremburg, but never stood trial. He continued a productive career in neuropathology and published extensively, including manuscripts utilizing material from euthanasia victims. He died in 1965, successfully escaping prosecution, but more recent information suggests that his involvement in Nazi crimes was more active than admitted. Herein, we conclude that Hallervorden’s 1954 paper should not be referenced as the first neuropathologic description of CTE pathology, and provide an up-to-date summary of his activities during the Third Reich to both remind ourselves and teach young neuropathologists of this dark period in the history of our field. The opinions expressed herein are those of the authors and are not necessarily representative of those of the Uniformed Services University of the Health Sciences, the Department of Defense, the United States Army, Navy or Air Force, or the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc. Saturday Posters   Neurodegenerative Disease 129 Neuropathologic Findings in Centenarians Spencer Tung1, Shino Magaki1, Christopher Williams1, Chao Peng2, Harry Vinters1 1UCLA Department of Pathology, Division of Neuropathology; 2UCLA Department of Neurology As the fastest-growing group in many industrialized countries, individuals over 90 years of age are at great risk for dementia with an incidence rate of approximately 40% per year. Clinicopathologic studies have suggested that neuropathologic substrates of dementia in centenarians are complex, with a preponderance of multiple co-morbidities that affect cognitive function. In this study, we examined pathologic findings in centenarians who underwent autopsy at UCLA Medical Center between 2000 and 2020. There was a total of 17 subjects, 12 with complete autopsies and 5 with brain only examinations. The average age at death was 106.4 + 5.8 years (ranging from 99 to 115 years; 4 males and 13 females). There was a wide spectrum of Alzheimer disease (AD) neuropathologic change with many subjects showing modest Alzheimerization of the brain despite their advanced age. Senile plaques were virtually absent in a few subjects but were abundant and widespread with amyloid deposition extending to the brainstem and cerebellum in others. Neurofibrillary tangles ranged from Braak and Braak stage III to VI. Cerebral amyloid angiopathy was seen in 10 subjects but was mild in severity in the majority. Only one subject had both cortical and substantia nigra Lewy body pathology, which co-occurred with severe AD neuropathologic change. No frontotemporal lobar degeneration was identified. Mild to severe atherosclerosis was observed in all subjects. Ten of the 17 cases demonstrated ischemic lesions which ranged from a solitary small cerebellar microinfarct to multiple deep gray lacunar infarcts and microinfarcts. Five subjects showed unilateral or bilateral hippocampal sclerosis. Our findings demonstrate that some extremely old individuals appear to have “resistance” to AD pathologic change; cerebrovascular disease may play a significant role in cognitive impairment among centenarians. 130 Prion Disease with Insertion of Two-octapeptide Repeats in the PrP Gene: Molecular and Phenotypic Determination Ignazio Cali5, Tze Mok1, Christiane Stehmann2, Laura Cracco3, Gianfranco Puoti4, Mark Cohen5, Steven Collins2, Simon Mead1, Brian Appleby6 1MRC Prion Unit at University College London, United Kingdom; 2Australian National Creutzfeldt-Jakob Disease Registry, Australia; 3Department of Pathology, Indiana University, Indiana; 4University of Campania “Luigi Vanvitelli”, Caserta, Italy; 5Department of Pathology, Case Western Reserve University, Cleveland, OH; 6Department of Neurology, Case Western Reserve University, Cleveland, OH Prion disease (PrD) is a rare but invariably fatal neurodegenerative disorder1. Its genetic form, which accounts for about 15% of all PrD, is caused by point mutations in the prion protein (PrP) gene as well as deletions or insertions, including those in the octapeptide repeat region of PrP. In the present study, we evaluated 8 subjects with 2-octapeptide repeat insertion (2-OPRI) mutation that were contributed by prion disease surveillance centers of United States (n=5), United Kingdom (n=2) and Australia (n=1). All cases were assessed for their clinico-pathological phenotype, genetic, and PrP molecular features. Repeat (R) sequence available in six cases revealed the presence of two extra repeats R2 (n=4), R2a-R2a (n=1) and R2-R3 (n=1) peptides; methionine (M)/valine (V) genotype at codon 129 showed M/M homozygosity (129MM) and M/V heterozygosity (129MV) in 5 and 3 cases, respectively. Disease penetrance was low (0.1-0.2%) and no patients had family history of prion disease. Clinical disease was representative of classic Creutzfeldt-Jakob disease (CJD) phenotype. Histopathology was indistinguishable from that of sporadic CJD MM1 (sCJDMM1) subtype in three 2-OPRI cases with codon 129MM genotype and disease-associated PrP (PrPD) type 1 (i.e., a major PrPD type of PrD), and it was characterized by fine spongiform degeneration and synaptic PrP deposition. Two other 2-OPRI cases had mixed PrPD types (1 and 2), and phenotypes of sCJDMM1-2 and sCJDMV2C+12,3. Remarkably, the western blot profile of 2-OPRI detergent-insoluble PrPD differed from that of sCJD. The present study indicates that 2-OPRI is a rare genetic variant and suggests that while differences in conformation of PrPD between inherited 2-OPRI and sCJD may exist, they are too subtle to lead to divergent disease phenotypes. 1Bonda et al., Neurosurg Focus, 2016;2Cali et al., Brain 2009;3Parchi et al., Acta Neuropathol 2009. Supported by: NIA K99/R00 AG068359 and CDC NU38CK00048. 131 Ubiquitin-positive Astrogliopathy Clinically Mimicking Parkinson’s Disease Meaghan Morris1, Abhay Moghekar2, Sonja Scholz3, Haidan Guo1, Olga Pletnikova4, Javier Redding1, Marilyn Albert2, Susan Resnick5, Liam Chen6 1Department of Pathology, Johns Hopkins University; 2Department of Neurology, Johns Hopkins University; 3Neurodegenerative Diseases Research Unit, NINDS; 4Department of Pathology and Anatomical Sciences, University at Buffalo; 5Laboratory of Behavioral Neuroscience, National Institute on Aging; 6Department of Laboratory Medicine and Pathology, University of Minnesota A variety of neurodegenerative pathologies can cause clinical Parkinsonism, some of which closely mimic sporadic Parkinson’s disease. The majority of these neurodegenerative diseases cause prominent loss of pigmented dopaminergic neurons in the substantia nigra, which is thought to underlie many of the clinical motor impairments. While several clinical mimics of Parkinson’s disease can show prominent glial pathology, often the aggregates are comprised of known pathogenic proteins such as tau and alpha-synuclein. Here we present an unusual case of a 91-year-old man with a clinical diagnosis of Parkinson’s disease. He was followed longitudinally as a participant of the Baltimore Longitudinal Study of Aging. He presented initially with dysphagia then progressed to Sinemet-responsive Parkinsonism, leading to a clinical diagnosis of Parkinson’s disease. His motor impairments and dysphagia progressed gradually over the next 13 years after the diagnosis in the absence of cognitive impairment. On post-mortem examination, there was no evidence of atrophy and the substantia nigra was well-pigmented. Immunostaining showed diffuse ubiquitin-positive glia throughout the cortex, striatum, and cerebellar cortex, with sparing of the substantia nigra. These aggregates were negative for tau, alpha-synuclein, TDP-43, and FUS. Tau immunostaining showed primary age-related tauopathy (Braak IV). This case is a rare example of an unknown glial neurodegenerative pathology clinically mimicking sporadic Parkinson’s disease. Unusually in this case, neuronal loss and ubiquitin pathology were not prominent in the substantia nigra despite the dopamine-responsive clinical symptoms. Further molecular studies are needed to gain insight into this rare neurodegenerative process. 132 Pathogenic Alpha-Synuclein is Present in the Kidneys of Lewy Body Disease Patients Liam Chen1 1University of Minnesota Medical School Background: Parkinson’s disease (PD) and dementia with Lewy bodies (DLB) are degenerative disorders of the central nervous system (CNS) with pathological hallmark of phosphorylated alpha-synuclein deposition in Lewy bodies (LBs) and Lewy neurites (LNs). Recently, population-based studies have revealed that patients with kidney diseases, in particular chronic kidney diseases are associated with a higher long-term risk of PD. Methods: Eleven patients with Lewy body disease (LBD), five healthy controls, and seven patients with end stage renal disease (ESRD) were examined for the presence of pathogenic phosphorylated alpha-synuclein at the residue serine 129 (pS129 alpha-synuclein) in kidney and brain. Results: Ten of eleven subjects with PD or DLB had accumulated pS129 alpha-synuclein in their kidneys. Although some of the healthy control kidneys contained detectable pS129 alpha-synuclein, all chronic renal disease patients had prominent α-synuclein pathology including LBs and Lewy neurites LNs in the CNS. Conclusion: Our observation has provided the first evidence that kidney may serve as another peripheral organ of initiation site for pathogenic alpha-synuclein to spread, suggesting compromised renal function might affect the risk of developing LBD. 133 Ataxin-2 Polyglutamine Expansions Sequester TDP-43 and Disrupt Trafficking and Dynamics of Neuronal TDP-43 RNA Granules Sonali Vishal1, Denethi Wijegunawardana1, Pallavi Gopal2 1Pathology Department, Yale University; 2Pathology Department, Yale School of Medicine, Yale University Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are profoundly debilitating and fatal neurodegenerative diseases with overlapping clinical, pathologic and genetic features. Despite advances in our understanding of the pathology and genetic basis of ALS/FTD, the cellular mechanisms underlying neurodegeneration remain poorly understood. Almost all ALS patients and nearly half of FTD patients have pathologic aggregates composed of TDP-43, a DNA and RNA-binding protein with multiple roles in RNA stability, splicing and post-transcriptional RNA processing. Moreover, mutations in TDP-43 and other RNA-binding proteins cause familial and sporadic ALS/FTD, highlighting altered RNA metabolism as a common pathogenic mechanism of neurodegeneration. Recent studies have identified genetic interactions between TDP-43 and Ataxin-2, an RNA-binding protein that contains a polyglutamine (polyQ) tract normally 22-23 glutamines in length. Expansions of the Ataxin-2 polyQ tract (27-33 glutamines) increase risk for ALS and FTD/Motor neuron overlap disease. However, the cellular and molecular mechanisms by which Ataxin-2 / TDP-43 interactions increase disease risk are unknown. Here we show that endogenous, wild type Ataxin-2 colocalizes with a subset of TDP-43 positive neuronal ribonucleoprotein (RNP) granules, which are dynamic liquid-like biomolecular condensates that regulate post-transcriptional RNA processing and exhibit bidirectional transport in the axon and dendrites. We find that RNP granules containing Ataxin-2 Q22 exhibit distinct spatial localization, predominantly within the proximal axon, motility, and function, compared to RNP granules composed of TDP-43. Moreover, using live cell imaging, we show that Ataxin-2 polyQ expansions disrupt the dynamic properties of TDP-43 RNP granules, including fluorescence recovery after photobleaching and the anterograde transport of TDP-43 RNP granules that contain mutant Ataxin-2. As a result, TDP-43 is sequestered within the proximal axon in the presence of Ataxin-2 polyQ expansions, which may have detrimental effects on the stability and localization of transcripts critical for axonal and cytoskeletal integrity, particularly in motor neuron axons. 134 Ultrastructure of PDE4D and HCN1 in Rhesus Macaque Entorhinal Cortex Layer II: Signature of Vulnerability in Alzheimer’s Disease Dibyadeep Datta1, SueAnn Mentone1, Yury Morozov1, Christopher van Dyck1, Amy Arnsten1 1Yale University Tau pathology emerges in a distinct spatial and temporal pattern in Alzheimer’s Disease (AD). Anatomical studies in AD subjects and rhesus macaques show earliest signs of tau pathology in the stellate cell islands in entorhinal cortex (ERC) layer II. However, the molecular mechanisms that confer vulnerability to ERC layer II cells early in AD is unknown. Our previous research in monkeys showed early calcium dysregulation in layer II ERC, where phosphorylated tau accumulated on the calcium-storing smooth endoplasmic reticulum (SER) under glutamatergic synapses, and PKA-phosphorylated ryanodine receptors on the SER showed evidence of calcium leak. cAMP-PKA magnification of calcium release has been seen in prefrontal cortex, associated with HCN channel opening to dynamically regulate synaptic strength. This process is regulated by phosphodiesterases (PDE), regulation that is lost with age. The current study examined whether this “signature of flexibility” could also be seen in layer II ERC, underlying vulnerability to tau pathology with aging. We used high-spatial resolution immunoEM to localize PDE4D and HCN1 in young rhesus macaque (7-10y) ERC layer II. PDE4D and HCN1 were primarily observed in postsynaptic compartments in macaque ERC layer II. In dendritic spines, PDE4D was concentrated on the SER spine apparatus and in postsynaptic density, and HCN1 expressed in the membrane near excitatory synapses. Within dendritic shafts, PDE4D labeling was observed along microtubules and near mitochondria, whereas HCN1 was organized in discrete clusters along the plasma membrane. These data suggest that PDE4D is optimally positioned to modulate cAMP microdomains and control calcium extrusion from the SER. HCN1 channels are localized in subcompartments to facilitate dynamic physiological representation of sensory experience and visual space governed by cAMP-PKA signaling. The anatomical patterns in ERC layer II corroborate our findings in vulnerable glutamatergic circuits in prefrontal cortex, suggesting conserved molecular features in association cortices most susceptible in AD. 135 Deep Learning-based Diagnostic Model for Alzheimer’s Disease, PSP, CBD, and Pick’s Disease Shunsuke Koga1, Dennis Dickson1 1Mayo Clinic Neuropathological assessment is the gold standard for diagnosing neurodegenerative disorders; however, the increasing number of patients with neurodegenerative disorders makes it critical to have scalable, cost-effective means for post-mortem diagnoses that can compensate for the dwindling number of neuropathologists. This study aimed to develop a deep learning-based diagnostic model for tauopathies, including Alzheimer’s disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick disease (PiD), using tau-immunostained digital slide images. We developed an object detection model for tau lesions using the YOLO object detection algorithm. We used digital whole slide images of CP13-immunostained slides of motor cortex from 10 cases each of AD, PSP, and CBD for training. Eighty to 100 images (500 x 500 pixels) were taken from each case, and the five representative tau lesions (neuronal inclusions, neuritic plaques, tufted astrocytes, astrocytic plaques, and coiled bodies) were annotated. In total, 2522 annotated images were used for training the model. Next, we made random forest classifiers using the quantitative burdens of each tau lesion from three brain regions (motor cortex, caudate nucleus, and superior frontal gyrus). A total of 100 cases (25 cases each of AD, PSP, CBD, and PiD) were divided into training (75 cases) and test (25 cases) sets to create random forest classifiers. To evaluate the model, we tested our model in a hold-out dataset of 33 cases (9 each of AD, PSP, and CBD, 6 PiD). Our object detection model achieved mean average precision of 75%. Training and testing scores of random forest classifiers were 1.00 and 0.97, respectively. In the hold-out dataset, 31 of 33 cases were correctly diagnosed (94% diagnostic accuracy). In conclusion, our deep learning-based diagnostic model can be a practical diagnostic tool for tauopathies, which can assist medical decision-making in neuropathological diagnoses of tauopathies by non-experts. 136 Neuropathology in the Life after 90 Study: A New Ethnically Diverse Cohort Study of Oldest-Old Brittany Dugger1, Lee-Way Jin1, Veronica Vargo1, Charles DeCarli1, Sharanpreet Johal1, Paola Gilsanz2, Dan Mungas1, Claudia Kawas1, Maria Corrada1, Rachel Whitmer1 1University of California, Davis; 2Kaiser Permanente Northern California Division of Research There is a dearth of neuropathology studies, in ethnically diverse, non-white decedents over age 90, although these persons are the fastest growing segment of the US population. In July 2018, the Life after 90 study began enrollment and is an ongoing cohort study of Kaiser Permanente Northern California members aged 90+ with recruitment across different racial/ethnic groups of individuals with no prior diagnosis of dementia in their medical record. Brain donation was available to all interested consenting participants. As of January 2021, 173 (26%) participants enrolled in autopsy (18% Asian, 12% African American, 12% Latino, and 10% as multiracial) with 8 deceased and neuropathological evaluations completed. Average age of death was 96 years (range 91 to 105), 5 (62.5%) were female, 3 Latino, 3 Caucasian, and 2 multiracial. The most common neuropathology was Age Related Tau Astrogliopathy and was found in 6 cases (75%). With respect to Alzheimer’s disease (AD), all participants had some level of neurofibrillary tangles with Braak stages between II and IV. Two participants lacked plaques (Amyloid-Beta or neuritic types), and the highest Thal phase was 4. Two met criteria for intermediate likelihood (25%), 4 low (50%), and 2 were considered not to have AD (25%); none had high likelihood of AD. Four participants (50%) had Lewy bodies (LBs), 1 in olfactory bulb/tract only, 2 Transitional, and 1 with Diffuse. Hippocampal sclerosis was not seen in any whereas TDP-43 inclusions were detected in 2 participants (25%). Diffuse LB, TDP-43 inclusions, and intermediate AD co-occurred in one (50%) of the dementia participants while all were lacking in the other. Preliminary results of the first 8 deaths in this multiethnic cohort of oldest-old individuals indicate that numerous brain pathologies are present with advanced age. Further work with this study will examine the clinical impact of this pathological heterogeneity. 137 A Case of Comorbid Amyotrophic Lateral Sclerosis and Progressive Supranuclear Palsy Daniel Kirsch1, Ann McKee1, Sarah Horowitz2, Rebecca Mathias1, Zachariah Foster2, Victor Alvarez2, Kerry Cormier3, Caroline Kubilus3, Thor Stein1, Bertrand Huber2 1Department of Pathology and Laboratory Medicine, Boston University; 2VA Boston Healthcare System, U.S. Department of Veterans Affairs; 3Veterans Affairs Bedford Medical Center We report a case of a 66-year-old male who initially presented with gait disturbances and difficulty breathing. Over the next six years, his physical and mental condition progressively deteriorated, and he was diagnosed with amyotrophic lateral sclerosis (ALS) antemortem. The patient died in hospice care, at which point he had lost the ability to perform any activities of daily living (ADLs). Upon neuropathological examination, there were skein-like hyperphosphorylated TAR DNA-binding protein 43 (pTDP-43) inclusions in remaining anterior horn cells of the spinal cord at all levels with moderate degeneration and gliosis of the spinal cord anterior grey matter and corticospinal tracts with sparing of the dorsal columns. There was also marked neuronal loss and gliosis of the motor cortex, consistent with a diagnosis of ALS with Stage I/IV cellular pTDP-43 pathology. There was pronounced neuronal and glial p-tau pathology throughout the frontal cortex, midbrain, and brainstem, with the subthalamic nucleus, substantia nigra, and pons particularly affected. Isoform-specific IHC staining demonstrated that the p-tau observed was composed of 4R tau. The p-tau neurofibrillary tangles in the substantia nigra and Rolandic cortex were predominantly globose-shaped. There were p-tau positive tufted astrocytes throughout the grey matter in the cortex, midbrain, and brainstem, and there were scattered p-tau positive astrocytes and oligodendroglial coiled bodies in white matter throughout the brain. The p-tau pathology observed was diagnosed as progressive supranuclear palsy (PSP). The coexistence of PSP and ALS in a single patient has been theorized but rarely neuropathologically diagnosed and described. This case report outlines the gross and histological findings in a patient with comorbid disease diagnosed at autopsy and highlights some more unusual features. 138 Brain Pathology of 18 Supercentenarians Aged 110 And Over Masaki Takao6, Ban Mihara1, Yasumichi Arai2, Tomoyuki Murakami3, Soichiro Nose4, Kazuo Hamaya4, Katsuya Nishida5, Naonobu Futamura5, Yuji Nakayama2, Masashi Mizutani6, Terunori Sano6, Yae Kanai2, Masaru Mimura2, Hideyuki Okano2, Nobuyoshi Hirose2 1Mihara Memorial Hospital; 2School of Medicine Keio University; 3NHO Kanmon Medical Center; 4Okayama Saiseikai Hospital; 5Hyogo-chuo National Hospital; 6National Center of Neurology and Psychiatry National Center Hospital According to the 2015 census, there were 146 of supercentenarians (SCs) (aged 110 and over) in Japan. We reported neuropathologic results of four SCs in 2016. Contrary to expectations, their brain pathologic changes such as distribution of neurofibrillary tangles and senile plaques were mild. Although the brain pathologic conditions with aging have been generally considered as progressive biological alterations as they grow older, our results suggested that the changes are not severe in extremely old individuals. Since 2016, we have obtained additional 14 brains of SCs. In the present study, we show the results of neuropathologic changes of 18 SCs. The genders were 2 men and 16 women. The average age of death was 112 ys (110 to 114 ys). ApoE genotype was 2/3 in two (11.1%), 3/3 in 13 (72.2%), and 3/4 in 3 cases (16.7%). Pathological findings of Alzheimer's disease (ADNC) were low in 9 cases (50%), intermediate in 7 cases (38.8%) and high in 2 cases (11.1%). Thal’s stage of amyloid-beta was A1 in 7 (38.8%), A2 in two (11.1%) and A3 in 9 (50%). Braak’s stage of neurofibrillary tangles was B1 in 5 cases (27.7%), B2 in 11 cases (61.1%) and B3 in 2 cases (11.1%). Seven cases (38.8%) were consistent with primary age-related tauopathy (PART). No hippocampal sclerosis was seen except for TDP-43 deposits. Lewy body pathology was present in one case. No major cerebrovascular diseases were seen. Our results support our hypothesis that extremely aged individuals have evidently healthy brains in terms of neurodegenerative changes associated with normal aging. Investigating the causes of mild changes of those brains would be important for elucidating the mechanism of longevity. 139 Automated Detection of Cerebral Amyloid Angiopathy in Amyloid Beta Stained Slides Using Trained Machine Learning Models Lise Minaud1, Daniel Wong1, Harry Vinters2, Mari Perez-RosenDahl3, Shino Magaki2, Edwin Monuki3, John Paul Graff4, Lee-way Jin4, Hollie Adams5, Sakshi Das4, Yamah Hamsafar4, Zin Hu4, Yan Hu3, Jerry Lou3, Alessandra Martini3, My-Le Nguyen4, Jana Tarabay3, Michael Keiser1, Brittany Dugger4 1Institute for Neurodegenerative Diseases, UCSF; 2University of California, Los Angeles; 3University of California, Irvine; 4University of California, Davis; 5Occidental College, Los Angeles Cerebral Amyloid Angiopathy (CAA) is defined by deposits of amyloid beta peptide in the walls of cerebral cortical and leptomeningeal vessels. It affects 30% of the neurologically-normal elderly and frequently co-occurs with Alzheimer's Disease (AD). Identifying and labeling the severity and anatomic locations of CAA can be a laborious and subjective task. We aim to provide a ground truth and a consistent, automated way to identify CAAs, as well as their anatomic location and severity. We used whole slide images (WSIs, n=95) from three different institutions. Each WSI was derived from formalin- fixed paraffin- embedded sections from the temporal, occipital, and frontal cortices immunostained with a variety of antibodies against amyloid beta. From the WSIs, we generated 19,998 tiles of candidate CAAs-affected vessels which were then annotated by 5 experts and 9 novices. For each tile, annotators labeled whether a CAA was present, its anatomic location (i.e. leptomeningeal vs. parenchymal), and the severity of blood vessel infiltration (Vonsattel criteria). Convolutional neural networks learned the 14 different annotation behaviors with average area under the receiver operating curve (AUROC) =0.92 ± 0.003 for leptomeningeal vessels and with average area under the precision recall curve (AUPRC) =0.68 ± 0.01 (baseline=0.26 ± 0.051), AUROC=0.91 ± 0.008 and AUPRC=0.68 ± 0.08 (baseline=0.15 ± 0.022) for parenchymal vessels, and AUROC=0.87 ± 0.018 for capillaries. We also show the model is robust and stable, with good performance on augmented data. This study is in agreement with previous work analyzing interrater variability in characterizing CAA by location and severity. We present a standardized, scalable method to characterize these pathologic findings to provide deeper histomorphologic phenotyping. 140 Novel Short Isoform TDP-43 Antibody Staining Pattern in Neurodegenerative Disease Patient Tissue Emile Pinarbasi1, Sean Ferris1, Sami Barmada1 1University of Michigan Amyotrophic lateral sclerosis (ALS) is a fatal and rapidly progressive neurodegenerative disease characterized by the cytosolic aggregation of the normally nuclear RNA-binding protein, TDP-43. A short isoform of TDP-43 (sTDP-43) has been reported which is upregulated with neuronal hyperactivity, accumulates in the cytoplasm, and forms insoluble cytosolic inclusions in cell culture models of ALS. However, sTDP-43 accumulation and distribution in patient tissue has not been characterized. We used an isoform-specific antibody directed against unique residues in the C-terminus of sTDP-43 to assess sTDP-43 localization and abundance. We examined selected brain regions (motor cortex, spinal cord, hippocampus, amygdala, and cerebellum) in patients with ALS, limbic predominant age-related TDP-43 encephalopathy (LATE), Alzheimer’s disease (AD), and other tauopathies. In concordance with cell culture data, weak staining for sTDP-43 was observed in a diffuse and predominantly cytoplasmic pattern throughout all assessed brain regions, with relatively increased granular staining in the neuropil of the posterior horn of the spinal cord. Surprisingly, sTDP-43 did not overlap with pathological TDP-43 inclusions in any disease state. Instead, sTDP-43 appeared to colocalize with granulovacuolar degeneration bodies (GVBs) seen in AD and other tauopathies. To date, no convincing role for TDP-43 has been described in the formation of GVBs, which are lysosomal structures thought to form in response to tau aggregation. We were unable to detect full-length or phosphorylated TDP-43 in GVBs, consistent with varied and inconsistent reports of these proteins within GVBs. Our findings suggest selective involvement of atypical TDP-43 splice variants in the formation and/or evolution of GVBs. 141 A FRET-based Reporter to Screen for Genetic Modifiers of Nuclear Inclusion Formation in Polyglutamine Disease Biswarathan Ramani1, Anthony Abarientos1, Giovanni Aviles1, Stephanie See1, Martin Kampmann1 1University of California San Francisco Abnormally expanded polyglutamine tracts in specific proteins are the cause of several inherited neurodegenerative diseases, including Huntington disease, several spinocerebellar ataxias, spinobulbar muscular atrophy, and dentatorubropallidoluysian atrophy. Most of these polyglutamine diseases are neuropathologically characterized by the accumulation and aggregation of misfolded mutant protein in the nucleus, and this is accompanied by the formation of distinct intranuclear inclusions. While studies have supported that the formation of nuclear inclusions is protective, this remains debated as the mechanisms underlying their formation are unknown. To begin identifying factors that drive inclusion formation, we have developed a new fluorescence resonance energy transfer (FRET)-based reporter with expanded polyglutamine tracts tagged with fluorescent mScarlet and mNeonGreen. Expression of this reporter in HEK293 cells leads to the formation of microscopically visible intranuclear inclusions that mirror those seen in human disease, and their formation correlates with the presence of a distinct FRET signal, which can be rapidly detected by flow cytometry. Using this robust and high-throughput assay, we will perform a genome-wide CRISPR screen to identify modifiers of nuclear inclusion formation. We plan to report the results of this novel screen at the AANP Annual Meeting, as well as ongoing efforts to uniquely perform screening and validation of hits in primary mouse neurons both in culture and in vivo. We expect the results of the screen to provide new insight into nuclear protein quality control pathways, along with more firmly establishing a protective versus toxic role for nuclear inclusions in polyglutamine disease. 142 TDP43 Proteinopathy in Patients with Huntington Disease Daniel Child1, Rebecca Yoda1, Suman Jayadev1, Thomas Bird1, C. Keene1, Caitlin Latimer1 1University of Washington Misfolded protein aggregation is a histopathologic hallmark of both sporadic and genetic neurodegenerative diseases. The instigating molecule and pattern of aggregation is well characterized for specific diseases, but the mechanism of pathogenesis is still poorly understood. Recent evidence supports a prion-like behavior for several misfolded proteins, including Tau and alpha-Synuclein, but it is unknown whether aggregates associated with one neurodegenerative disease are capable of seeding aggregation-prone proteins associated with unrelated diseases. Here, we present the case of a Huntington disease (HD) mutation carrier who unexpectedly developed lower motor neuron symptoms, including fasciculations, weakness, and hyporeflexia. The patient was clinically diagnosed with amyotrophic lateral sclerosis (ALS), which progressed rapidly, with death four years after symptom onset. Post-mortem examination demonstrated histopathologic and immunohistochemical evidence of both HD and ALS including huntingtin-positive aggregates throughout the basal ganglia and frontal cortex, and TDP-43 positive inclusions within upper and lower motor neurons. Notably, a second case with concomitant clinical diagnoses of HD and ALS was identified within the University of Washington brain bank and at least twelve similar cases have been reported in the literature. According to current epidemiologic estimates, the independent likelihood of these two diseases occurring simultaneously is 2.38 per billion, and the existence of multiple cases at a single clinical location is more frequent than would be expected by chance. To further probe this potential interaction, a large-scale evaluation of HD brains for concurrent TDP43 pathology is currently underway. These cases of comorbid HD and ALS suggest that misfolded aggregating proteins may be able to seed unrelated protein aggregation, and thus patients at risk for or with an existing neurodegenerative disease may be at increased risk for additional neurodegenerative disease processes. Further investigation into the common biochemical mechanisms of aggregation may produce novel therapeutic modalities to treat multiple diseases. 143 Distinct Disease Phenotypes and PrP Type 1 Variants in Creutzfeldt-Jakob Disease with Codon 129MM Genotype Rabeah Bayazid1, Rabail Aslam1, Yvonne Cohen1, Lawrence B. Schonberger5, Mark L. Cohen1,4, Brian S. Appleby1,2,3,4, Ignazio Cali1,4 Departments of 1Pathology, 2Neurology, 3Psychiatry and 4National Prion Disease Pathology Surveillance Center (NPDPSC), Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA; 5 Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA Sporadic Creutzfeldt-Jakob disease (sCJD) is classified into five phenotypically distinct subtypes based on the different electrophoretic mobility of the disease-associated prion protein (PrPD), identified as PrPD type 1 (T1) and type 2 (T2), and the methionine (M)/valine (V) genotype at codon 129 (129MM, -MV or -VV)1. The sCJD subtypes include MM(MV)1, VV1, MM2, MV2 and VV2. Sporadic CJDMM1, the most common subtype, is typically associated with protease-resistant PrPD T1 and is phenotypically characterized by fine spongiform degeneration that predominates in the cerebral cortex and by the lack of PrP amyloid plaques. However, sCJDMM1 with prominent PrPD kuru-type plaque pathology has recently been described2,3. In a retrospective analysis of 523 cases with sCJDMM1 (n=366), -MM2 (n=48) or mixed -MM1-2 (n=109) subtypes, we detected PrPD plaques in 14 cases (2.7%). Plaques (p) populated either the grey matter (pGM-sCJD, n=7), where they were confined to the cerebellar cortex, or the white matter (pWM-sCJD, n=7) throughout the brain. Importantly, the two PrP plaque phenotypes were associated with distinct gel mobilities of T1. These findings bring to focus the issue of PrPD amyloid plaques in sCJDMM patients and suggest that distinct T1 PrPD variants are modifiers of disease phenotype. Experiments to test this hypothesis as well as possible explanations for why these cases are different from typical sCJDMM cases are underway. 1Parchi et al., Ann Neurol. 1999; 2Kobayashi et al., Acta Neuropathol. 2008; 3Rossi et al., Acta Neuropathol Communic. 2017. Supported by: NIA K99/R00 AG068359 grant to I. Cali, CDC NU38CK00048 to B. Appleby. As a trainee of the research education component (REC) of the Cleveland ADRC, the work of I. Cali was supported by the NIA P30 AG062428 01. 144 Analysis of Soluble Proteins Implicated in Alzheimer’s Disease From Formalin Fixed Paraffin Embedded Human Brain Tissue Jaclyn Lilek1, Kaouther Ajroud2, Callen Spencer1, Ivan Ayala1, Allegra Kawles1, Tamar Gefen1, Evangeline Bambakidis1, Alexander Feldman2, M. Mesulam1, Qinwen Mao2, Changiz Geula1, Robert Vassar3, Eileen Bigio2, Margaret Flanagan2 1Northwestern University, Mesulam Center; 2Northwestern University, Department of Pathology; 3Northwestern University, Department of Neurology Introduction: Several proteins have been implicated as pathologic culprits in Alzheimer’s Disease (AD). Studies have demonstrated correlations between cognitive impairment and soluble Aβ (sAβ) levels, as well as tau and TAR DNA-binding protein 43 (TDP-43). Extraction of soluble proteins from formalin fixed paraffine embedded (FFPE) human brain tissue was previously optimized in our lab using a homebrew extraction buffer. This is an ideal method for utilizing banked FFPE tissue for proteomic analyses. Soluble proteins can be quantified using assays for multiplexing and increased sensitivity such as Meso Scale Discovery (MSD). Methods: Nine human brains from the Northwestern University Alzheimer’s Disease Center brain bank, representing varying stages of AD neuropathology, were fixed with either paraformaldehyde (PFA) or neutral buffered formalin (NBF), and blocks were embedded in paraffin. Blocks of frontal cortex, basal ganglia, and cerebellum from each case were then cut into 3 curls, each 14 microns thick, and deparaffinized in xylene. Soluble proteins were extracted using 100mM Tris protein extraction buffer (PEB). Extracts were analyzed for total protein concentration via BCA. Western blots and ELISAs were performed for validation to confirm presence and quantify the of proteins of interest: sAβ, tau, and TDP-43. Triplicates of each sample were used to assess consistency. Results: When comparing detection of sAβ, tau, and TDP-43 in samples extracted from FFPE human brain tissue, the resulting trends were consistent with those detected in samples extracted from fresh frozen human brain tissue. Conclusions: Soluble proteins extracted from FFPE human brain tissue can be used for comparative analyses of soluble proteins implicated in AD. 145 Quantification and Staging of Neurofibrillary Degeneration Using Deep Learning Juan Vizcarra1, Bart White2, John Crary3, Marla Gearing2, Michael Keiser4, Kurt Farrell3, Bailie Schock2, Brittany Dugger5, David Gutman2 1Georgia Institute of Technology and Emory University; 2Emory University; 3Icahn School of Medicine at Mount Sinai; 4University of California San Francisco; 5University of California, Davis The use of semi-quantitative scoring systems for assessment of neurodegenerative disease pathologies is the gold-standard but has limitations. Reliability is often decreased in the intermediate affected cases where stratification of the scoring systems appears to be too fine for consistency in larger studies. Deep learning approaches have been recently shown to work well for detecting neuropathologic markers in whole slide images (WSIs). Such approaches could provide more consistent results while also augmenting the ability of the neuropathologist. Here, we extend these early findings by exploring the application of deep learning workflows for the task of quantification of neurofibrillary tangles (NFTs) in multiple brain regions (including amygdala, hippocampus, temporal, and occipital cortices) in cases across the spectrum of Braak NFT stages (n=52) from the Goizueta Emory Alzheimer’s Disease Center brain bank with a goal of implementing computer-assisted hierarchical NFT staging. A multi-institutional collaboration of expert and novice annotators were recruited to generate a large number of NFT digital annotations (n>9,000). Inter-rater reliability was investigated to assess the variation among experts for Braak staging (k=.90, 95% CI: 0.85 – 0.94)) in our cohort and the variation among both experts and novices in NFT annotations. We are implementing various deep learning workflows using the annotated dataset to develop NFT detection models for individual annotators and ensembles (combination of annotators) and to generate WSI-level heatmaps of NFT. WSI heatmap interpretation could potentially be used to create computational scores of pathology burdens across an entire case for comparison with semi-quantitative equivalent scores (Braak staging). Additionally, these heatmaps could be overlaid with previous methods that similarly generated amyloid beta WSI heatmaps, allowing a novel multi-layered pathology assessment. Together this work investigates the effectiveness of deep learning workflows for an important neuropathologic task, focusing on potential utility in practice. 146 Neuropathologic Findings in a Patient with Clinical Kluver Bucy Syndrome Samantha Champion1, Bradley Hyman1, Matthew Frosch1 1Massachusetts General Hospital Neurodegenerative diseases are diagnosed clinically using a combination of tools including history, physical examination, imaging, and additional tests, such as CSF studies. Neuropathologic examination then confirms the clinical diagnosis. Infrequent instances occur were a neuropathologic diagnosis is discrepant. A 72-year-old woman presented with short-term memory changes. Over 9 years she developed progressive cognitive and behavioral impairments including hyperorality and hypersexuality, consistent with Kluver Bucy syndrome. Brain MRI at age 76 showed diffuse cortical and hippocampal atrophy. CSF studies showed a pattern in the “consistent with Alzheimer’s disease” quadrant using the ADMARK algorithm (Aß42: 790.9 pg/ml; T-Tau: 806.25 pg/ml; P-Tau: 85.3 pg/ml; ATI: 0.66). She continued to decline and expired at age 83. At autopsy, the brain showed marked superior frontal cortical thinning with temporal lobe atrophy, including mild atrophy of the anterior hippocampus. The cingulate gyrus, anterior commissure and fornix were atrophic. The amygdala, basal ganglia and thalami were normal. Microscopic examination showed significant TDP-43 proteinopathy with heaviest burden within the frontal, cingulate and temporal lobes, including the amygdala and hippocampus. There was a predominance in the upper cortical layers with neuronal cytoplasmic inclusions and short dystrophic neurites, consistent with frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP), Type A. While some injury to the amygdala was present, the TDP-43 pathology was not more severe than other cases of FTLD-TDP. Immunohistochemistry showed tau staining limited to the medial temporal lobe and hippocampal subsectors CA2 and CA4, with no beta amyloid staining. These neuropathological results are not concordant with the CSF findings. This is case of a patient with a dementia syndrome and conflicting CSF/ neuropathological results. Clinicians and Neuropathologists should be aware of the possibility for these clinicopathologic discrepancies. 147 Clinicopathologic Heterogeneity of TBK1 Mutations: Report of Two Cases Rebecca Yoda1, Danny Miller2, David Ivanick3, Thomas Bird3, B. Jane Distad3, Suman Jayadev3, Caitlin Latimer1 1Division of Neuropathology, University of Washington, Seattle, WA; 2Division of Medical Genetics, University of Washington, Seattle, WA; 3Department of Neurology, University of Washington, Seattle, WA Mutations in the TANK-Binding Kinase 1 (TBK1) gene have been implicated in a spectrum of neurologic disease. Clinical presentations most commonly include frontotemporal dementia (FTD) and motor neuron disease (MND), with additional reports of extrapyramidal symptoms and cerebellar manifestations. The full clinical spectrum of patients with TBK1 mutations has not been explored in detail, and neuropathological reports are scant. We report the clinicopathologic features of two unrelated patients with familial TBK1 alterations. The first decedent was a 60-year-old man clinically diagnosed with FTD and MND. FTD was also suspected in multiple family members. Genetic studies identified a TBK1 mutation (p.Arg117*). The second decedent was a 64-year-old woman clinically diagnosed with MND with prominent bulbar involvement. Family members demonstrated variable clinical phenotypes including ataxia, FTD, and amyotrophic lateral sclerosis (ALS). A novel TBK1 variant (c.358 + 3A>G) was identified in the decedent and two siblings. Postmortem neuropathologic examination of both cases revealed TDP-43 pathology with distinct distributions. Histopathologic findings in case 1 included temporal-predominant parenchymal vacuolation and scattered TDP-43-immunoreactive neuronal and glial cytoplasmic inclusions, more prominent in the amygdala and hippocampus than in neocortex, most consistent with frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), type B. In addition, there was mild loss of anterior horn cells with scattered TDP-43-positive inclusions, consistent with ALS. Case 2 demonstrated TDP-43-positive inclusions in motor cortex with associated parenchymal degenerative changes and only corticospinal tract degeneration in spinal cord, most consistent with primary lateral sclerosis (PLS). Of note, tau pathology did not follow typical Braak staging patterns, but instead partially overlapped with the distribution of TDP-43 pathology. These cases enrich our current knowledge of TBK1-related pathology by characterizing clinical and neuropathologic features associated with a novel mutation and by highlighting the clinicopathologic heterogeneity among patients with TBK1 mutations. 148 Histologic Comparison of Homozygous and Heterozygous Cases with the A431E Mutation in PSEN1 Samuel Guzman1, John Ringman1, Kymry Jones1, Carol Miller1, Helena Chui1 1University of Southern California Keck School of Medicine The Jalisco variant of autosomal dominant Alzheimer’s disease (ADAD) associated with the A431E substitution in PSEN1 is known for having an early onset and aggressive clinical course of dementia, frequently co-occurring with spastic paraparesis. Commonly, this variant is associated with characteristic non-neuritic, cotton-wool plaques (CWPs), largely consisting of Aβ42. Here, we present histological differences between a rare homozygous A431E variant case (dying at age 39 years) and three A431E heterozygous cases (47-59 years old) that have a later clinical onset of symptoms. By H&E, the homozygous case demonstrated occasional granulovacuolar degeneration (GVD) and neuron loss in CA2/CA1 of the hippocampus and cortical neurons compared to diffuse GVD, and severe pyramidal neuron loss throughout the hippocampus and the neocortex in the heterozygous cases. Analysis of hyperphosphorylated Tau (pTau) (AT8 IHC and Gallyas staining) in the heterozygous group revealed a higher density of neurofibrillary tangles and neuropil threads in the hippocampus and neocortex compared to the homozygous case. However, Aβ42/40 plaque loads (Aβ42/40 IHC staining), with emphasis on quantifying CWPs, revealed minimal differences between the two groups in the hippocampus, temporal and frontal lobes, and cerebellum. Evaluation of axonal density (Neurofilament 200 IHC) in the heterozygous group revealed severe loss of axons in CA1-CA4 of the hippocampus and cortical layers 3-6 of the frontal and temporal lobes and absent staining near CWPs. The homozygous case also demonstrated minimal staining near CWPs, and a decrease in axonal staining in CA4 with a slight decrease in axons of CA3/CA2 and a near complete loss in CA1 of the hippocampus. These histologic differences, with the homozygous case showing relatively minor pTau pathology despite comparable Aβ pathology, may reflect different points along the ADAD pathological continuum in which the downstream effects of amyloid are mitigated in the homozygote. 149 Biochemical Analyses of Neuronal Markers in Human Brains and Submandibular Glands in the Setting of Alzheimer’s Disease Yamah Hamsafar1, Zin Hu1, Qian Chen1, Alexander Borowsky1, Thomas Beach2, Geidy Serrano2, Lucia Sue2, Charles Adler3, Brittany Dugger1 1University of California, Davis; 2Banner Sun Health Research Institute; 3Mayo Clinic Arizona Tau protein hyperphosphorylation in the brain can lead to neuropathology in Alzheimer’s disease (AD). Previous biochemical studies demonstrated select tau species to be present in the submandibular gland (SMG) with differential levels based on AD diagnosis. This study examined the extent and type of tau (an unmodified human tau species (HT7), and pT231) as well as other neuronal proteins (microtubule associated protein 2 (MAP2), phosphorylated neurofilament (NF), and tyrosine hydroxylase (TH)) in human brain and SMG. Biochemical analyses were conducted on soluble fractions of frontal cortex gray matter and SMG tissues from the same cases (n=18, 3 not/low, 6 intermediate, and 9 high AD likelihood based on NIA Reagan criteria). When examining pT231 with increased likelihood of AD, there was a trend for select species to be decreased in the SMG, while increased in the frontal cortex. MAP2 and NF were detectable in soluble fractions in frontal cortex and SMG while TH was only detectable in SMG. Although sample sizes were small, these data suggest specific protein alterations in AD in both the brain and SMG. This study is the first to our knowledge to investigate a plethora of neuronal proteins using similar methods in human SMG and brain tissues of the same cases. Additional works having more cases are warranted. 150 A Case of Frontotemporal Lobar Degeneration with FUS Pathology (FTLD-FET) with Corticobasal Syndrome and Language Deficits Vanessa Goodwill1, David Coughlin1, Donald Pizzo1, Lawrence Hansen1, Shauna Yuan2, Annie Hiniker1 1University of California San Diego; 2University of Minnesota We report a pathologically confirmed case of aFTLD-U with atypical clinical features and subtle pathology. A 56-year-old man presented with progressive language and behavioral problems over a year and a half, including non-fluent aphasia and impulsivity. Initially, he was diagnosed with frontotemporal dementia. MRI showed mild global atrophy and FDG-PET scan showed markedly decreased uptake in the bilateral caudate and putamen. Three months later, he re-presented with a history of increased falls, right hand apraxia and contraction with dystonic posturing. His working diagnosis was revised to corticobasal syndrome. The patient died at age 58 approximately two years after presentation. At autopsy, gross examination of the brain revealed mild atrophy of the frontal and temporal cortex, and severe atrophy of the caudate, putamen, and hippocampus. Microscopically, there was minimal neuron drop-out and astrogliosis in the neocortex, but prominent hippocampal sclerosis and neuron loss and gliosis of the neostriatum. Immunohistochemistry for tau revealed only rare tangles in the entorhinal cortex. b-amyloid, a-synuclein, and TDP-43 IHC stains were negative. Frequent rounded neuronal cytoplasmic inclusions and scattered intranuclear filamentous inclusions were identified within dentate granule cells of the hippocampus on ubiquitin, FUS and TAF-15 staining. Sparse TAF15 inclusions were also seen in the basal ganglia, pons, and frontal cortex. The morphology and distribution of inclusions was consistent with aFLTD-U. aFTLD-U is an uncommon form of FTD characterized by the accumulation of the FET family of proteins, including FUS, EWS, and TAF15, that usually presents at a young age (20s-40s) with prominent behavioral symptoms, and a relative lack of motor and language abnormalities. Here we report an unusual case of aFTLD-U with an older age of onset, prominent motor and language abnormalities, including features of corticobasal syndrome, and subtle pathology. This case further expands the phenotype of the rare, and possibly under-recognized entity of aFTLD-U. 151 A Case of Adult Neuronal Ceroid Lipofuscinosis (Kufs’ Disease) Nicholas Haslett1, William Humphrey1, John DeWitt1 1University of Vermont Medical Center Kufs’ Disease is a rarely diagnosed disease that is a late-onset neuronal ceroid lipofuscinosis (NCL) marked primarily by intraneuronal accumulation of subunit C of mitochondrial ATP synthase (SCMAS). Presentation of NCL varies, but may involve disorders of cognition, motor systems, or vision. We present the case of a 54-year old male with a history of neurocognitive decline, behavioral changes, and seizure activity. Prior to his first seizure episode 13 years ago, the patient was healthy with no major medical issues. The patient first experienced a generalized tonic clonic seizure in 2007 followed by simple partial seizure activity. During that time, he lost his ability to work, lost a significant amount of weight due to inconsistent eating, demonstrated increased disorganized thinking and worsening memory along with irritability and outbursts of anger. Autopsy examination of the brain revealed neurons throughout the brain with swollen luxol fast blue-positive inclusions consistent with a metabolic storage disorder, with the most prominent accumulation of storage material seen within pyramidal neurons of the hippocampus. This storage material was also strongly PAS-positive. Ultrastructural examination of the hippocampus showed finger print profiles and curvilinear bodies. These findings are most consistent with adult neuronal ceroid lipofuscinosis (ANCL), a rare adult-onset form of Batten's disease, also known as Kufs' disease. A number of different genes have been implicated in the development of ANCL, with the majority of cases inherited in an autosomal recessive manner. Although genetic confirmation is not available in this case to confirm the diagnosis, given the possibility of a genetically heritable disorder, genetic counseling for surviving family members may be appropriate. 152 MM2 Thalamic Form of Creutzfeldt-Jakob Disease With the PRNP M232R Mutation Terunori Sano1, Hotake Takizawa2, Yuji Saitoh2, Kentaro Matsui1, Masashi Mizutani1, Yoko Shigemoto3, Noriko Sato3, Katsuya Sato4, Tetsuyuki Kitamoto5, Yuji Takahashi2 1Department of Laboratory Medicine, NCH, National Center of Neurology and Psychiatry; 2Department of Neurology, NCH, National Center of Neurology and Psychiatry; 3Department of Radiology, NCH, National Center of Neurology and Psychiatry; 4Department of Health Sciences, Nagasaki University Graduate School of Biomedical Science; 5Department of Neurological Science, Tohoku University Graduate School of Medicine Introduction: The MM2 thalamic form of sporadic Creutzfeldt-Jakob disease (CJD) is a rare phenotype. Although the M232R mutation of the PRNP gene has been reported as one of the pathogenic mutations of CJD, several studies have suggested that this mutation might be a genetic polymorphism. Clinical course: A 68-year-old Japanese man developed gait disturbance. He showed parkinsonism and cognitive decline 3 months after the onset. He was admitted to our hospital 6 months after the onset. Neurological examination showed dementia, pyramidal signs, extrapyramidal signs, cerebellar ataxia, and autonomic dysfunction. His Mini-Mental State Examination score was 6/30. Sleep disturbance was also recorded. Repeated electroencephalograms did not reveal any periodic synchronous discharges. Magnetic resonance images showed diffuse atrophy of the cerebrum, cerebellum, and thalamus, without hyperintense lesions on diffusion-weighted images. Total tau, 14-3-3 protein, and RT-QuIC levels in the cerebrospinal fluid were normal. PRNP gene analysis revealed a heterozygous mutation M232R with 129M/M and 219E/E. Eleven months after the onset of symptoms, he died of malnutrition. Neuropathology: The fresh brain weight was 1,248 g. There was slight atrophy of the frontal and temporal lobes, as well as moderate atrophy of the bilateral thalamus. Microscopic examination showed severe neuronal loss and gliosis at the level of the thalamus and inferior olivary nucleus. There were rare and small spongiform changes in the temporal and frontal cortices. These lesions showed coarse PrP-immunoreactive deposits using monoclonal antibodies 3F4 and 12F10. Western blot analysis showed abnormal type-2 PrPres in the thalamus, frontal lobe, and temporal lobe. The patient was diagnosed with the MM2 thalamic form of CJD. Discussion: A pure MM2 thalamic form carrying the M232R mutation is extremely rare. The relationship between the M232R mutation and the MM2 thalamic form requires further investigation. 153 A Clinicopathological Case Presentation of Corticobasal Degeneration Peng Cheng Han1, Robert Schmidt1 1Washington University in St Louis School of Medicine Corticobasal degeneration (CBD) is a rare progressive neurological disorder. While it typically presents with motor symptoms initially, cardinal symptoms may also include cognitive deficit and/or task difficulty. Here we present a case with clinical presentation as a cognitive problem and the pathological findings are highly characteristic of corticobasal degeneration. The patient was a 73-year-old Caucasian woman with a 10-year history of difficulty in solving problems and a 4 year history of language difficulty. She was assessed in 2018 with a clinical dementia rating (CDR) of 0.5, or mildly impaired. MRI performed at that time showed cortical atrophy involving frontal and parietal lobes bilaterally (left > right) and possible prior/remote subarachnoid hemorrhage involving the left frontal and temporal lobes. The patient passed away in an assisted living facility. No interim clinical information is available prior to her death on 8/2020. Postmortem brain examination identified atrophic cortex involving bilateral frontal cortical gray matter (Left > Right in severity) and left temporal lobe, diminished subcortical white matter of the centrum semiovale, substantial dilatation of lateral ventricles and blunting of their angles bilaterally in the frontal and temporal horns, and reduced pigmentation of the substantia nigra. Major microscopic findings include cortical neuronal loss with astrogliosis, superficial microvacuolation, abundant achromatic balloon cells, astrocytic plaques and Tau immunoreactive glial inclusion (coiled bodies). These features were found, to various degrees, throughout frontal, temporal, insular cortices, as well as deep grey matter including basal ganglia and thalamus, but spared cerebellar deep nuclei and minimally involved pons/medulla. These geographical features are characteristic of corticobasal degeneration. In addition, limited localized neuritic plaques, sparse TDP43 proteinopathy, and restricted frontal cortical distribution of Lewy bodies suggest mixed additional neurodegenerative features. However, these mild changes may not have significantly contributed to the major clinicopathological course. 154 A Case of Pick’s Disease Presenting with Corticobasal Syndrome Yuanyuan Gu1, Qi Zhang2, Stephen Pasternak3, Lee Cyn Ang2 1Department of Pathology, Western University, Canada; 2Department of Pathology, University Hospital and Western University, Canada; 3Department of Neurology, University Hospital and Western University, Canada Introduction: Pick’s disease (PiD) is a rare form of frontal temporal lobar degeneration. It usually presents with behavior changes and aphasia. The primary pathology is atrophy of the frontotemporal lobes. The pathognomonic feature is intraneuronal deposits of 3R-Tau inclusions, the Pick body. We report a case of PiD presented with corticobasal syndrome (CBS). Case presentation: A 62-year-old female presented with agraphia which progressed to aphasia and hand apraxia. Other symptoms included worsening in memory, visual-spatial and frontal executive function. There was paratonia with increased tone and cogwheeling in the right arm. Her right hand was clenched and would not open voluntarily. MRI revealed asymmetrical temporal lobe atrophy (left more severe than right) and left lateral ventricle enlargement. A clinical diagnosis of CBS was raised. A trial treatment with Aricept and Memantine was not effective. Her symptoms gradually deteriorated. She passed away at the age of 75. Pathology: Macroscopic examination reveals general cerebral atrophy, with marked left frontotemporal atrophy and mark dilation of the lateral ventricles. Microscopically, severe neuronal loss and gliosis were observed, as well as numerous intraneuronal cytoplasmic basophilic inclusions present in multiple regions, including all sampled cerebral cortex, bilateral hippocampi and amygdala, basal ganglia, thalamus and brain stem. The left side was more severely affected than the right side. Immunohistochemistry revealed the cytoplasmic inclusions are positive for 3R-Tau; negative for 4R-Tau, alpha-synuclein, and TDP-43, consistent with Pick bodies. Conclusion: PiD presenting with CBS is rare. There are only a handful of cases reported at the time of preparing this abstract. Pick’s disease should be considered as a differential diagnosis for patients presenting with atypical parkinsonism. 155 Advances in Deep Neuropathological Phenotyping of Alzheimer’s Disease: Past, Present, and Future Mustafa Shakir1, Brittany Dugger1 1University of California, Davis Alzheimer’s disease (AD) was first described in 1906 by Alois Alzheimer, and since then there has been many advancements that have aided in unlocking the secrets of this devastating disease. Such advancements include improved microscopy techniques, refined diagnostic criteria for the disease, and an increased appreciation of disease heterogeneity both in neuroanatomic location of abnormalities as well as overlap with other brain diseases, such as Lewy body disease and vascular dementia. In this presentation, we will delve into the history of these notable advancements and their importance to the field. We will also touch upon recent technological advancements such as incorporating machine learning algorithms to establish scalable deeper neuropathologic phenotyping for the disease, enhancing precision medicine approaches for AD. Tumors 2 156 Crooke Cell Adenoma with Aggressive Features: Histologic Spectrum and Diagnostic Pitfalls Nichole Allen1, Chandra Vysha2, Chandani Pate3, Whitney Woodmanse3, Brian Lobo4, Steven Roper2, Marie Rivera-Zengotita5 1University of Florida; 2University of Florida College of Medicine Department of Neurosurgery; 3University of Florida College of Medicine Department of Medicine; 4University of Florida College of Medicine Department of Otolaryngology; 5University of Florida College of Medicine Department of Pathology Crooke cell adenoma is a rare variant of corticotroph (ACTH-positive) pituitary adenoma characterized histologically by the presence of ring-like cytoplasmic accumulation of filaments that displace secretory granules to the submembrane region. Clinically, Crooke cell adenoma may be silent or present with Cushing’s disease and demonstrate an increased risk for aggressive biologic behavior including invasion of adjacent structures and potential for recurrence. We present a 43-year-old woman with history of rheumatoid arthritis and multiple sclerosis who presented with epistaxis. Imaging revealed a 3.2 x 3.0 x 2.7 cm heterogeneously enhancing lobular mass in the sella that extended into the sphenoid sinus, nasal cavity and cavernous sinuses. The patient underwent subtotal resection of the mass. Intraoperative consultation revealed a highly pleomorphic tumor with non-uniform cells showing aggressive cytological features. Permanent sections revealed a cellular neoplasm composed of markedly atypical epithelioid cells, including multinucleated forms, arranged in sheets and pseudopapillae demonstrating increased mitotic activity and focal necrosis. There was organizing hemorrhage and a mixed inflammatory infiltrate in areas of apparent sinus invasion. Tumor cells were immunoreactive for cytokeratin AE1/3, chromogranin, ACTH, and Tpit. CAM5.2 showed strong cytoplasmic ring-like positivity in tumor cells. The Ki-67 proliferation index was elevated (approximately 10%). A recent study (Casar-Borota et al. J Clin Endocrinol Metab, Oct 26 2020) showed that ATRX mutations occur in a subset of aggressive corticotroph adenomas. Our tumor demonstrated focal loss of nuclear immunoreactivity for ATRX suggestive of mutation. On follow up, CT scan of the chest, abdomen and pelvis showed no evidence of metastatic disease. Due to the aggressive clinical and histologic features of the tumor, radiation therapy was recommended. This case highlights the histologic spectrum of Crooke cell adenoma. A panel of immunohistochemical studies that include transcription factors is essential for distinguishing these tumors from their mimics including metastatic carcinoma. 157 Lymphomatosis Cerebri as a Presentation of Secondary Central Nervous System Lymphoma (SCNSL) Hao Li1, Basma AlYamany1, Michael Shkrum1, Lee-Cyn Ang1 1Schulich School of Medicine and Dentistry, Western University A lymphoma involving the brain diffusely without formation of a discrete mass lesion is best characterized as lymphomatosis cerebri. While such a presentation is well-described in primary central nervous system lymphoma (PCNSL), our autopsy revealed a clinically undiagnosed lymphoma outside the CNS which disseminated secondarily to the brain. A 72-year-old female presented with abdominal pain. A CT showed bilateral adrenal hemorrhages. Treatment with steroids resulted in symptomatic improvement. However, she soon developed confusion, stroke-like symptoms, and decline in consciousness. Serial MRIs demonstrated progressive extensive asymmetrical leukoencephalopathy with abnormal enhancement but no mass effect. Multiple investigations were nonrevealing. Given a working diagnosis of demyelinating encephalomyelitis, she was managed with more steroids and intravenous immunoglobulin without a biopsy diagnosis. She eventually developed refractory status epilepticus, and died shortly afterwards. Post-mortem examination revealed extensive infiltration of the brain, left kidney, and adrenal glands by a diffuse large B cell lymphoma, which also involved the lung and peripancreatic tissue. CNS involvement included cerebral grey and white matter, brainstem, cerebellum, and minimally the leptomeninges. Lymphomatous infiltrate was mostly angiocentric. The neuropathology was typical of a lymphomatosis cerebri. Lymphomatosis cerebri is a lymphoma exhibiting diffuse infiltration of the CNS without forming any discrete mass(es). It is often mistaken for non-neoplastic entities such as inflammatory or demyelinating conditions. While it is known as a very uncommon presentation of PCNSL (review of 42 cases, Izquierdo et al., Neuro Oncol. 2016 May; 18(5): 707–715), its occurrence in SCNSL is exceptionally rare. Our case reinforces the concept that a radiological presentation of leukoencephalopathy may actually be a lymphoproliferative neoplasm. Furthermore, the neoplasm may be secondary, necessitating extensive clinical investigations to rule out a lymphoma outside of the CNS. 158 A Case of Diffuse Leptomeningeal Glioneuronal Tumor Misdiagnosed as Bacterial Meningitis Alaa Alkhotani1, Emad Alkhotani2, Syeddah Mujtaba3, Shahad Isa4 1Um AlQura University, Pathology Department, King Abdullah Medical City; 2Radiology Department, King Abdullah Medical City; 3Pathology Department, King Abdullah Medical City; 4Um AlQura University Diffuse leptomeningeal glioneuronal tumour (DLGNT) is a newly added entity to the 2016 2016 World Health Organization (WHO) classification of central nervous system. It most commonly affects children and young adults and is characterized by extensive leptomeningeal proliferation of oligodendroglioma-like cells with neuronal differentiation and common molecular alteration. We present a case of a 22-year-old blind man who was referred to our hospital with a history of headache, nausea and vomiting for two months. The patient was referred as a case of bacterial meningitis with communicating hydrocephalus and high CSF protein level. Neuroimaging demonstrated extensive supra and infratentorial leptomeningeal enhancement with left parasagittal occipital heterogeneously enhancing lesion. Biopsy was done and microscopic examination showed nests of hypocellular tumour. The tumour had small round nuclei, inconspicuous nucleoli, and perinuclear halos. The tumour cells were positive for GFAP, olig2 and synaptophysin and were immune-negative for IDH1, BRAFV600E and EMA. The Ki67 were less than 1%. Based on the microscopic and immunohistochemical features of the tumour, the diagnosis of DLGNT was made. Due to its rarity, DLGNT has been misdiagnosed frequently. DLGNT should be considered in the differential diagnosis in patients with diffuse leptomeningeal enhancement and high CSF protein. Tissue diagnosis is recommended in such cases. 159 INI-1 Deficient Sinonasal Carcinoma Presenting as a Neurosurgically Encountered Skull Base Tumor Mahmoud Aldyab1, Jiang Qian1 1Albany Medical Center Hospital/College The skull base is a junction between intracranial and extracranial head/neck structures. Neoplasms of the skull base can be primary, metastatic or direct tumor extension from surrounding sites. INI-1 deficient sinonasal carcinoma (INI-1-DSC) is a newly-described sinonasal malignancy representing a subset of previously termed sinonasal undifferentiated carcinoma (SNUC). INI-1-DSC can secondarily infiltrate nearby intra- and/or extra-cranial structures. Here we report an unusual case of INI-1-DSC which presented as a primary skull base mass. A 46-year-old man was admitted for double vision, facial numbness, eye pressure, and Horner’s syndrome. Imaging revealed a 4.1 cm skull base tumor extending into right cavernous sinus and pterygopalatine foramen with erosion of adjacent bones. Pathologic examination following surgical removal demonstrated a high-grade carcinoma composed of sheets and nests of epithelioid cells with conspicuous nucleoli, low N-C ratio, brisk mitoses, necrosis and marked desmoplasia. The tumor was positive for cytokeratins, EMA, P16, P40 and P63, negative for IDH-1, Synaptophysin, Vimentin and EBER, and totally devoid of INI-1 staining. Molecular analysis confirmed loss of the SMARCB1 (INI-1) gene. He underwent radiation therapy, but later developed metastases to thoracic spine and ilium. At follow-up two years after surgery, no local recurrence was detected. Sinonasal malignancies are uncommon (5% of all head/neck cancers). With molecular techniques, several entities of SNUC are reclassified as NUT-rearranged carcinoma and INI-1-DSC, among others. First described in 2014, INI-1-DSC is among a group of tumors including atypical teratoid/malignant rhabdoid tumors and epithelioid sarcoma which share loss of the tumor suppressor gene SMARCB1 (INI-1). INI-1-DSC is a high-grade malignancy affecting males and females equally over a wide age range (mean 52), with 54% of patients died within 8.5 years. This case illustrates the importance of recognizing INI-1-DSC in neuropathologic/neurosurgical practice treating skull base tumors since this sinonasal tract derived malignancy can present at unusual sites. 160 Anaplastic Astrocytoma with IDH1 R132G and PALB2 Mutations: A Case Report Omid Rashidipour1, Benjamin Cho1, Mary Fowkes1, Christopher Kellner2, Nadejda Tsankova1, Jane Houldsworth1, Clare Bryce3, Melissa Umphlett4 1Department of Pathology, Mount Sinai Hospital; 2Department of Neurosurgery, Icahn school of Medicine at Mount Sinai West; 3Mount Sinai Hospital; 4Department of Pathology, Mount Sinai Hospital at Mount Sinai West Introduction: IDH1 R132G is a rare variant of IDH mutation that occurs in only about 1% of IDH-mutant astrocytomas versus the more commonly encountered R132H mutation which occurs in nearly 93% of cases. Case Report: We present the case of a 32-year-old female with a history of colon polyps who developed headache and left-sided weakness while returning from a run. Head CT revealed several hemorrhagic lesions in the right fronto-parietal region with vasogenic edema and bilateral uncal and downward herniation. She underwent an emergent right-sided decompressive hemicraniectomy. Resection specimen revealed anaplastic astrocytoma, WHO 3, negative for IDH1 R132H by immunohistochemistry, pending molecular studies for final IDH mutational status. Additionally, there was no loss of nuclear expression of MMR proteins detected by immunohistochemistry. Post-operatively, the patient experienced multiple episodes of ventricular tachycardia and expired two days later. A full unrestricted autopsy was performed 49 hours after death. Pertinent family history for this patient included breast cancer in her mother, and her father was recently deceased after diagnosis and treatment for glioblastoma. Results/Discussion: Next-generation sequencing analysis of DNA from this patient identified clinically significant variants in the IDH1 R132G, ATRX, TP53, and PALB2 genes. Although the test performed is not validated to report germline variants, the PALB2 p/Q988* pathogenic nonsense variant detected was thought to possibly be germline in origin. Currently, limited survival data exists regarding the more elusive IDH1 R132 subtypes like R132G and R132C. There is an emerging body of evidence that suggests these subtypes have different biochemical properties with prognostic significance, and with novel targetable agents, possible therapeutic implications. In addition, the association of PALB2 mutation in high grade gliomas is not well characterized, and in the setting of a rare IDH1 R132 subtype, has not previously been described. 161 A Rare Presentation Of Low-Grade Prostate Adenocarcinoma As Delayed Solitary Pineal Region Metastasis: A Case Report Misha Movahed-Ezazi1, Karin Skalina2, Kalind Parashar2, Alexandre Vdovenko1, Sunil Manjila2, Christopher Iannuzzi2 1Hartford Hospital; 2St. Vincent’s Medical Center Introduction: Prostate cancer is the most common cancer and the second leading cause of cancer death among American men. The most common locations of prostate cancer metastases are the axial skeleton, pelvic lymph nodes and the lung. Within the English literature, there have been two postmortem cases of metastases to the pineal gland and only one documented case of a living patient with prostate cancer metastasis to the pineal gland that underwent treatment with stereotactic radiosurgery. Case Presentation: A 75-year-old male with a past medical history of a Gleason 6 (3 + 3) prostate adenocarcinoma (status post external beam radiation therapy and continued androgen deprivation therapy) presented to the emergency department with altered mental status, dizziness and increased generalized fatigue. Physical examination showed unsteady gait with no neurological deficits. CT scan of the brain without contrast at the time of admission demonstrated a solid, cystic, calcified pineal lesion measuring 2.0 cm. At time of pineal gland lesion the patient’s PSA was 10.8. The patient underwent third ventriculostomy and biopsy, revealing a metastatic prostatic adenocarcinoma of the pineal gland. Discussion: Early clinical presentation of intracranial prostate metastases without initial metastases to other sites is extremely uncommon and has been documented in several case reports. Studies have shown that both high PSA and high Gleason score can be useful determining risk and likelihood of brain metastases in these patients. The therapeutic approach to pineal region tumors require multidisciplinary input and generally include surgical intervention followed by radiation therapy. A specific approach to pineal metastases related to prostate carcinoma is currently undefined. Conclusions: In this report, we present the second reported case of confirmed prostate cancer metastasis to the pineal gland in a living patient. Furthermore, the patient presented with a low-grade prostatic adenocarcinoma (Gleason 6) and no other prior sites of metastases. 162 Intracranial Metastasis from Prostate Adenocarcinoma: A Case Report and Review of the Literature Ahmed Lazim1, Yuan Rong1, Nirag Jhala1 1Temple University Hospital Introduction: Unlike lung, breast, melanoma, colon, and kidney cancers, which commonly spread to the brain, intracranial metastasis from prostate adenocarcinoma is rare and typically occurs in the setting of widely disseminated bone and soft tissue disease. We report a case of brain metastasis from prostate adenocarcinoma 16 years later after the initial diagnosis of prostate cancer. Case report: A 60 year old male patient with a clinical history of stage IV prostatic adenocarcinoma in 2005, status post prostatectomy in 2008 and complaints of headaches found a 8.1 x 4.3 x 2.3 cm bifrontal mass on CT scan, suspicious for metastasis. Microscopically, it demonstrates relatively monotonous tumor cells with prominent nucleoli and forming glandular structures. Tumor cells are positive for CK AE1/3, PSA, PSAP, and Racemase, but negative for CK7 and CK20. These results support a diagnosis of metastatic prostate adenocarcinoma. Discussion: Prostate adenocarcinoma commonly metastasizes to the pelvic lymph nodes, axial skeleton, and lungs. Brain metastases from prostate adenocarcinoma are rare and usually due to advanced systemic disease. Most of the metastases are intraparenchymal or dural-based. The Gleason scores at the time of diagnosis ranged from 6 to 9 according to the literature. Patients with non-adenocarcinoma morphology are more likely to develop brain metastases. Conclusion: Despite its rarity, prostate cancer should be considered in the differential diagnosis of intracranial metastases. Aggressive treatment of the metastatic site including tumor resection and radiation therapy may result in a better outcome. 163 Rare Histology of a Common Pediatric Brain Tumor (Medulloblastoma) Roger Fecher1, Raquel Yokoda1, Andrew Kobets1, Rick Abbott1, Steven Chin1 1Montefiore Medical Center Medulloblastomas are one of the most common pediatric malignancies, accounting for 20% of pediatric malignant CNS tumors. Medulloblastomas are a high-grade (WHO grade IV) embryonal tumor with characteristic histologic and molecular findings with biological significance. Histologically, medulloblastomas typically fit into several categories including classic, large cell anaplastic, nodular/desmoplastic, extensively nodular medulloblastoma (MBEN), biphasic (mixed classic and nodular), and infrequently medullomyoblastoma and melanotic medulloblastoma. However, other rare ‘biphasic’ morphologies have been reported in the literature. Gene expression profiling has allowed molecular classification into four groups: WNT pathway activation, SHH pathway activation, and Groups 3 and 4 often associated with MYC amplification. Here we present a case of a medulloblastoma with WNT-activation; while these molecularly defined medulloblastomas are typically associated with classic and more rarely large cell anaplastic histomorphology, here we present a case with a rare ‘biphasic’ appearance. In this tumor, we identified both areas with classic features without significant anaplasia and areas with slightly large uniform cells with bland nuclei embedded in a florid hyalinized matrix – a morphologic pattern that we did not identify in the literature. Here we review the literature of rare ‘biphasic’ medulloblastomas and provide a case that demonstrates a unique histologic pattern of medulloblastoma. 164 Molecular Profiling of a Ganglioglioma in the Setting of Neurofibromatosis Type 1 Kliment Donev1, Aditya Raghunathan2, Rachael Vaubel2, Robert Jenkins2, Leland Hu1, Richard Zimmerman1, Cristiane Ida2 1Mayo Clinic Arizona; 2Mayo Clinic Minnesota Ganglioglioma is a MAPK pathway-driven low-grade neuroepithelial tumor that has only rarely been reported in individuals with neurofibromatosis type 1 (NF1) syndrome. Here, we describe the molecular profile of a ganglioglioma arising in the setting of NF1. A 40-year-old female with clinical diagnosis of NF1 syndrome who presented with a two-year history of seizures. Imaging studies revealed a cystic left posterior frontal lobe brain tumor with enhancing mural nodules. Perfusion studies indicated increased relative cerebral blood volume in the mural nodules, and the tumor was resected. Histologic examination revealed a low-grade glioma with predominant neuronal component with dysmorphic and binucleated cells, and a relatively minor glial component showing low-grade fibrillary astrocytoma morphology. Rosenthal fibers were focally present at the tumor periphery. No eosinophilic granular bodies, calcifications, mitotic activity, tumor necrosis or microvascular proliferation were identified. Areas showing prominent capillary-type vasculature were observed, possibly contributing to the regions showing increased perfusion by imaging studies. The neuronal component was highlighted by synaptophysin, with rare CD34-positive cells, while the glial component was positive for GFAP and OLIG2. IDH1-R132H immunostain was negative and ATRX showed preserved nuclear expression. Targeted 219-gene neuro-oncology NGS panel revealed an NF1 L844R mutation, which has been reported as an NF1-associated germline mutation but not as a somatic mutation, at a variant allele frequency suggestive of germline origin. No additional sequence variants (including BRAF) or gene rearrangements were detected. Chromosomal microarray revealed a relatively balanced genome with isolated gains of chromosomes 7, 9 and 11, a pattern frequently seen in sporadic ganglioglioma. Copy number changes (including copy neutral loss of heterozygosity) involving NF1 were not apparent. The observed molecular profile in this case further supports the notion that MAPK pathway activation in NF1-associated ganglioglioma is independent of BRAF alterations and more similar to NF1-associated pilocytic astrocytoma than to sporadic ganglioglioma. 165 Polymorphous Low-Grade Neuroepithelial Tumor of the Young in a 47-Year-Old Man Presenting with Headache and Visual Deficits Marwan Majeed1, Christopher McMillan2, Jasmin Jo3, K. Lee4, Caitlin Sippey4, Dimitri Trembath5, Philip Boyer3 1East Carolina University/Vidant Medical Center; 2Brody School of Medicine, East Carolina University; 3East Carolina University; 4Vidant Neurosurgery/Vidant Health; 5University of North Carolina Background: Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently-described, low-grade, primary central nervous system neoplasm which typically presents with seizures. Case Report: A 46-year-old man presented with worsening headaches, blurred vision, and photophobia with no seizure history. Brain magnetic resonance imaging identified a cortex-based left temporoparietal, solid and cystic lesion with no contrast enhancement. Gross total resection was undertaken. Histology revealed an infiltrative neoplasm with cells variably demonstrating ovoid to spindled nuclei with process formation or a rounded nucleus with inconspicuous process formation and, in some, perinuclear halos. Variable immunoreactivity for glial fibrillary acidic protein and CD56 and focally striking CD34 expression in neoplastic cells. Occasional eosinophilic granular bodies but no Rosenthal fibers were noted. Abnormal collections of neurons, some multinucleated, with synaptophysin and NEU-N immunoreactivity were noted. No specific glioneuronal elements, floating neurons, ballooned neurons, or cortical lamination was identified. FGFR2-CTNNA3 fusion was detected with no mutations in IDH1, IDH2, ATRX, TP53, or BRAF and no 1p/19q codeletion. Final diagnosis was low-grade neurepithelial tumor consistent with PLNTY. He is followed by MRI evaluation every six months with stable findings 1.5 years postoperatively. Postoperative ophthalmologic evaluation identified right inferior greater than superior hemianopsia. Literature Review: Approximately 34 cases have been published, ages 4- to 57-years, average 18.2. Seizures were documented at presentation in 21 of 25 cases for which symptoms were reported with visual disturbance reported in 1. FGFR2 translocation was identified in 8 of 34 patients with FGFR2-CTNNA3 fusion transcript in 2; BRAF V600E mutation was identified in 15 of 34 patients. Conclusion: This case adds to the growing literature regarding the diagnosis and treatment of PLNTY with (1) the second oldest individual reported to date at 46-years (oldest: 57-years), (2) presentation in the absence of seizures, and (3) stable surgical site 1.5 years postoperatively. 166 Intracranial Primary Effusion Lymphoma with Exclusive Leptomeningeal Involvement M. Adelita Vizcaino1, Rebecca King1, Derek Johnson2, Caterina Giannini1, Aditya Raghunathan1 1DLMP, Mayo Clinic, Rochester, MN; 2Department of Radiology, Mayo Clinic Rochester, MN Primary effusion lymphoma (PEL) is a rare human herpesvirus 8 (HHV-8)-associated large cell non-Hodgkin lymphoma, typically harboring Epstein-Barr virus (EBV) coinfection, affecting young to middle-aged immunocompromised patients, particularly in the setting of human immunodeficiency virus (HIV) infection. PEL usually presents as lymphomatous effusions in pleural, pericardial, and peritoneal cavities in the absence of solid tumors or extra-cavitary masses. Central nervous system (CNS) involvement is exceptionally rare. Here, we present a case of a 60-year-old HIV-positive man. Magnetic resonance imaging (MRI) of the brain revealed patchy leptomeningeal enhancement over the paramedian posterior frontal lobes bilaterally, left parietal lobe, posterior fossa, and VII-VIII cranial nerve complex bilaterally. No discrete leptomeningeal or parenchymal masses were identified. Histologically, the leptomeninges were infiltrated by atypical cells with large nuclei and prominent nucleoli. By immunohistochemistry, these were positive for CD138, MUM-1, and HHV-8, as well as demonstrating aberrant CD3 expression, and negative for CD5, CD15, CD20, CD30, PAX5, Cyclin D1, and ALK-1. These cells were also positive for Epstein Barr virus-encoded RNA (EBER) by in-situ hybridization. The overall clinico-pathological findings supported the diagnosis of PEL. Primary effusion lymphoma is an unusual type of lymphoma that classically involves fluid compartments, and only a subset develops adjacent or extracavitary solid tumors, with the gastrointestinal tract being the most frequently involved site. This unique presentation of PEL affecting the CNS, as exclusive leptomeningeal involvement in the absence of systemic disease or discrete mass lesions, has not been previously described to the best of our knowledge. 167 p53 Positivity Comparison Between Automated Image Analysis Workflow and Trained Pathologists in Gliomas Lokman Cevik1, Diana Thomas1, Michelle Felicella2, Jose Otero1 1The Ohio State University; 2University of Texas Medical Branch Background: Immunohistochemical analysis of p53 and ATRX are commonly used in gliomas. p53 mutation and ATRX loss is an important factor for prognosis and treatment. Although some special techniques present for the positivity of IHC stainings, there is no completely objective way to determine p53 and ATRX positivity. Also, different thresholds are used for binary positivity results. We aimed to develop an automated positivity calculation workflow and to compare the results with trained pathologists. Methods: 82 diffusely infiltrating glioma images were evaluated by 2 trained pathologists and the automated image analysis workflow. Observer 1 evaluated the positivity percentage with eyeballing and observer 2 used a special technique for the positivity percentage. For automated workflow, we used the color deconvolution method for cell segmentation and extracted the pixel intensity and textural features of cell nuclei using the EBImage package in R. A Random Forest (RF) modeling was made using the cell nuclei in positive and negative controls and was used for the prediction of positive and negative nuclei in the images. We compared p53 positivity percentage and binary positivity results between the automated workflow and observers. For the evaluation of any bias of ATRX results on the p53 positivity, observers evaluated the same p53 images with ATRX images in a scrambled order. Results: p53 positivity percentage of automated workflow is much higher than the observers’. The concordance rate of the automated workflow with observer 1 is 69.5% and with observer 2 is 63.4%. After adding ATRX information, the concordance rates increased to 82.4% and 65.9%, respectively. The concordance rate between the p53 and p53 with ATRX information for observer 1 was 81.1% and for observer 2 was 97.6%. Conclusion: An open-source automated workflow can make the positivity results more objective, time-efficient and prevent discrepancies between the pathologists. 168 Intracranial Myxoid AFH/Mesenchymal Tumor with EWSR1-CREB Fusion Eric Goold1, Joshua Klonoski1, Lorraina Robinson1, Cristina Antonescu2, Ting Liu1, Cheryl Palmer1 1University of Utah; 2Memorial Sloan Kettering Cancer Center A woman in her thirties presented with left arm numbness, left-sided weakness and vision changes. Imaging studies revealed an enhancing right parietal lobe cortical enhancing mass that appeared to have a dural tail. Resection of the tumor was performed and histology demonstrated a myxoid spindle cell neoplasm with variable cellularity associated with a prominent vascular network. The tumor cells contained scant cytoplasm and ovoid nuclei with minimal nuclear pleomorphism. A prominent peripheral lymphoid cuff and absence of mitotic activity were also noted. Immunohistochemical staining demonstrated weak staining for epithelial membrane antigen (EMA) and focal staining for desmin; whereas SSTR2, S100, CD3, estrogen receptors, progesterone receptors, and glial fibrillary acidic protein were all negative. Fluorescence in situ hybridization showed an EWSR1-CREB fusion. Overall the clinical presentation, tumor morphology and immunoprofile were consistent with either a myxoid variant of an atypical fibrous histiocytoma or one of a handful of cases proposed to represent a new tumor entity provisionally called a myxoid mesenchymal tumor with EWSR1-CREB fusion. This hybrid gene produces a chimeric protein and novel transcription factor composed of the N-terminal transcription-activating domain of the EWS RNA binding protein 1 (EWSR1) with the C-terminal DNA-binding domain of cyclic AMP responsive element binding protein (CREB). Although no amianthoid fibers were present in this case, focal and weak desmin and EMA staining, lack of a fibrous pseudocapsule or cystic hemorrhagic spaces along with a relatively young patient age and uneventful short term follow up at six months, this case resembles those described as myxoid mesenchymal tumors. 169 Multiply Recurrent and Metastatic Olfactory Neuroblastoma with BRCA2 and SMARCA4 Mutations Joshua Klonoski1, Eric Goold1, Lorraina Robinson1, Cheryl Palmer1 1University of Utah A 45-year-old man with a history of multiply recurrent olfactory neuroblastoma presented for seizures. Imaging demonstrated a dural-based left temporal tip mass. A resection was performed and histology showed sheets and nodules of tumor cells separated by fibrovascular septae. The cells were characterized by abundant eosinophilic cytoplasm and moderately pleomorphic nuclei with salt and pepper chromatin. Scattered mitoses, large caliber vessels, lymphocytic infiltrates, hemorrhage and hemosiderin were present. Multifocal sharp demarcation with reactive brain parenchyma was also noted with an absence of rosettes and pseudorosettes. Immunohistochemistry (IHC) showed that tumor cells were positive for synaptophysin (SYN) and focally positive for p63 while epithelial membrane antigen (EMA) and CD3 highlighted dura and rare T-cell infiltrates, respectively. A MIB1 proliferation index was 20% and the tumor was negative for cellular adhesion molecular (CAM) 5.2, progesterone receptor (PR) and S100. Additional outside laboratory testing demonstrated 0% PD-L1 expression by IHC and massively parallel sequencing (MPS) demonstrated low tumor mutation burden (0 muts/Mb), microsatellite stability and two variants of unknown significance (BRCA2 Y3035C and SMARCA4 K1511R). In consideration of this case, three recent large MPS studies of 74 olfactory neuroblastoma (ONB) cases showed that while pharmacologic genetic aberrations occurred in up to 51% of cases, highly recurrent variants were not detected. Furthermore, DNA methylation testing of 42 cases of ONB strengthened diagnostic criteria of nest-stroma histoarchitecture, homogenous chromogranin/SYN staining and predominantly absent cytokeratin immunoreactivity. Given these recent advances and strengthening of diagnostic criteria for ONB, the present case is consistent with metastatic olfactory neuroblastoma. Interestingly, a single previous case of a recurrent ONB has been reported with a SMARCA4 (G1232S) mutation but additional mutation in beta- catenin (CTNNB1 N387K) as well as MYC and LYN amplification were present. The significance of these ONB cases with SMARCA4 mutations is currently unknown and requires more study. 170 Thyroid Transcription Factor-1 Expression in SEGAs and Cortical Tubers From TSC Patients Samantha Champion1, Anat Stemmer-Rachamimov1 1Massachusetts General Hospital Subependymal giant cell astrocytomas (SEGAs), WHO grade I, are benign astrocytic neoplasms that are associated with tuberous sclerosis complex (TSC). Diagnosis of SEGAs can be complicated as they may closely resemble high-grade gliomas, specifically giant cell glioblastomas. However, recent studies have shown that thyroid transcription factor-1 (TTF-1) is present in SEGAs and absent in high-grade astrocytomas. This may suggest lineage-restricted histogenesis as the NKX2-1 homeobox gene that encodes TTF-1, is temporarily expressed in the ventral forebrain during development of the embryo. The histogenesis of SEGAs, however, is still unclear. In order to explore the association between TTF-1 expression and TSC, we analyzed a panel of cortical tubers and SEGAs for TTF-1 expression. Our panel included sixteen SEGAs from sixteen patients with TSC (9 males and 7 females; age range 1 to 34-years-old) and ten separate cortical tubers from ten TSC patients (5 males and 5 females; age range: 2-weeks-old to 38-year-old). A case of glioblastoma with a prominent giant cell component was also evaluated for TTF-1 expression. TTF-1 expression was noted in 10/16 (63%) of the SEGAs. All the cortical tubers and the glioblastoma were immunonegative for TTF-1. In conclusion, most of the examined SEGAs are immunopositive for TTF-1 while none of the cortical tubers show immunopositivity. This shows TTF-1 expression is not a characteristic of all TSC-associated lesions in the central nervous system. In addition, while expression for TTF-1 may be helpful in the diagnosis of SEGA when positive, the lack of expression does not exclude the diagnosis of SEGA. 171 Marginal Zone Lymphoma Presenting as a Primary Dural Lesion: Report of Two Cases and a Review of the Literature Michael Williams1, Christine Fuller1, John Frederiksen1 1SUNY Upstate Medical University Lymphomatous involvement of the central nervous system (CNS) may be either secondary to systemic lymphoma or confined to the CNS at presentation (primary CNS lymphoma). In the latter instance, diffuse large B cell lymphoma presenting as single or multiple intraparenchymal lesions occurs most frequently, though a wide variety of other lymphoma subtypes may also be encountered. Dural-based lymphomas are relatively rare, and by neuroimaging are often mistaken for meningiomas or other more common neoplasms. The most frequent primary dural lymphoma is extranodal marginal zone lymphoma, with the majority of affected patients’ disease limited to the dura. Herein, we present two cases of dural-based extranodal marginal zone lymphoma. In the first, a 79-year-old woman with a recent diagnosis of marginal zone lymphoma of the skin of the right neck presented 2 weeks later with headaches and a palpable right scalp lesion. Imaging revealed an enhancing right frontoparietal dural lesion with overlying skull base bony erosion and a leftward midline shift. In the second case, a 70-year-old woman with no significant past medical history presented with syncopal episodes. Imaging revealed a left frontoparietal convexity dural-based mass with vasogenic edema and underlying osseous invasion and destruction. Surgical specimens from both patients showed an atypical diffuse lymphoid infiltrate within dural tissue with morphologic and immunohistochemical findings diagnostic of marginal zone lymphoma. IGH/IGK gene rearrangement studies performed on the specimen from the second patient confirmed the presence of a monoclonal B cell population, supporting the diagnosis. These cases emphasize that marginal zone lymphoma may present with primary dural involvement, which can manifest clinically either as a solitary intracranial lesion or as satellite extracranial lesions that mimic systemic lymphoma. 172 Round Cell Sarcoma With EWSR1-PATZ1 Gene Fusion Mimicking Malignant Peripheral Nerve Sheath Tumor Khaled Alkhateeb1, Brian Williams1, Alaleh Esmaeili Shandiz1, Julieann Lee2, Arie Perry2, Eyas Hattab1 1University of Louisville; 2University of California San Fransisco Malignant peripheral nerve sheath tumors (MPNST) are soft tissue tumors with neuroectodermal differentiation that typically show highly cellular fascicules of spindle cells. We hereby present a spindle and round cell sarcoma with neuroectodermal differentiation and EWSR1-PATZ1 gene fusion, morphologically and immunophenotypically mimicking MPNST. A 30-year-old man presented with progressive headache and dysphonia. Imaging revealed a large left sphenoid mass extending into the skull base and involving the right jugular foramen. CT scan of the abdomen additionally revealed a large right kidney mass. Biopsies from both masses demonstrated overlapping histologic features, showing highly cellular malignant neoplasms with fascicular spindle cell and round cell morphologies. The neoplastic cells showed a high nuclear-to-cytoplasmic ratio with scant pale eosinophilic cytoplasm and nuclei with fine chromatin and inconspicuous nucleoli. The tumor cells demonstrated immunoreactivity with S100, SOX10, synaptophysin, GFAP, and CD99 (cytoplasmic) and were negative for MART1, HMB45, CD34, desmin, and SMA. Expression of INI1 and H3K27me3 was retained. Next-generation sequencing performed on both tissue sites revealed EWSR1-PATZ1 gene fusion as well as CDKN2A and CDKN2B homozygous deletions. EWSR1-PATZ1 round cell sarcoma is a newly described neoplasm with spindle and round cell morphologies and frequent neuroectodermal differentiation. The histologic and immunophenotypic overlap with MPNST was notable. Awareness of this genetically distinct entity would greatly aid in reaching an accurate diagnosis. 173 DNA Methylation Patterns in an Ependymoma Patient-derived Orthotopic Xenograft Model Zainab Siddiq1, Ahmed Gilani2 1University of Colorado, School of Public Health; 2University of Colorado Anschutz Medical Campus, Department of Pathology DNA methylation is a known regulator of gene transcription but the extent to which it plays a role in regulation of gene expression in patient-derived orthotopic xenograft (PDX) models is unknown. Previously Pierce et al (Neuro Oncol. 2019 Dec 17;21(12):1540-1551) reported a PDX model of childhood posterior fossa ependymoma. While the PDX into the mouse 4th ventricle and subcutaneously into the flank retained many of the histological features of the original tumor and conformed to the same methylomic class on the German Brain Tumor Classifier, more than 700 genes were upregulated and approximately 3500 were down regulated. We explored whether DNA methylation changes can account for some of these transcriptomic alterations. Genome-wide DNA methylation levels at CpGs were obtained using 850K EPIC array. 2 samples of the patient tumor from the original surgical resection were compared to 2 PDX samples implanted in mouse flank. Data were analyzed using customized packages in R including minfi for importing IDAT files. Following normalization using the SWAN method, poor quality probes with a detection p-value <0.01 were filtered out. Beta and M-values were extracted, and a test for differential methylation was carried out using the limma package, which employs an empirical Bayes framework based on Gaussian model theory. The decidetests function in limma was used to obtain the numbers of hyper-methylated and hypo-methylated CpGs in one group compered to the other. No significantly up or down methylated regions were obtained. Candidate genes which showed differential expression between the patient sample and the PDX showed no significant changes in methylation. These data confirm that DNA methylation patterns are robust and are maintained in a PDX model. In conclusion, gene expression changes in PDX are likely explained by non-DNA methylation regulatory mechanisms. 174 A One-year Institutional Experience of the Diagnostic Utility of Routine Next-generation Sequencing in 91 Adult Gliomas Matthew Wood1, Tanaya Neff2, Amy Schilling2, Dan Farquhar2, Carol Beadling2, Christopher Corless2 1Department of Pathology, Oregon Health & Science University, Portland, OR; 2Knight Cancer Institute, Oregon Health & Science University, Portland, OR Central nervous system tumor classification relies on integrating tumor histology with molecular features. Tumor genetic profiling can also resolve a challenging differential, change an assigned histological grade, and/or suggest targeted therapies. This study analyzes the diagnostic impact of routine next-generation sequencing (NGS) in a cohort of adult gliomas diagnosed at our institution in 2020. Tumor nucleic acids were analyzed on a DNA sequencing panel covering 225 target genes, with fusion and splice variant detection of 20 genes detected by RNA sequencing. Copy number abnormalities, microsatellite instability status, and tumor mutation burden were also reported. The cohort included 91 primary diagnostic samples from 56 male and 35 female patients (median age 57; range 20-87 years). Glioblastoma (GBM) was the most common histological diagnosis (n=55; 60%), with most of the remaining cases being other types of diffuse glioma (n= 25; 27%). Sequencing results supported a change in the assigned World Health Organization (WHO) grade or in the histological classification in 8 cases (8.1%), of which 7 were histologically WHO grade 2 or 3 diffuse astrocytic gliomas with molecular features of GBM, thus raising them to grade 4. Molecular information was required for integrated diagnosis in 10 cases (11.0%), with 9 of these accounted for by detecting 1p/19q-codeletion and/or IDH gene mutations other than IDH1 p.R132H. Sequencing revealed potential therapeutic targets or resolved a histological differential in another 14 cases (15.4%). This group included targetable fusion events involving BRAF, RAF1, and NTRK2, tumors harboring BRAF p.V600E mutation, and histologically ambiguous diffuse gliomas categorically resolved by the NGS results. Overall, next-generation sequencing findings impacted tumor diagnosis, grading, or treatment options in 35% of the cohort. Utility was highest in patients over age 54 with non-GBM histology (13 of 15 cases; 87%), and in patients under 55 with any histology (17 of 29 cases; 59%). 175 Pituitary Carcinoma with ATM and ATRX Mutations and a Clinically Significant Gain in the CCND2 Gene Zachary Grimes4, Edward Wolin1, Saadi Ghatan2, Melissa Umphlett3 1Department of Hematology and Oncology, Mount Sinai Hospital; 2Department of Neurosurgery, Icahn School of Medicine. Mount Sinai West; 3Department of Pathology, Mount Sinai West; 4Mount Sinai Hospital Introduction: Pituitary carcinoma is extremely rare and comprises 0.1 to 0.2 percent of all pituitary neoplasms. Due to the rarity of this tumor, the molecular features are poorly understood. Case Report: We present a case of a 58-year-old male with a past medical history of acromegaly, pituitary adenoma, status post resection in 2013, tobacco abuse and diabetes. The patient presented with a chief complaint of right lower back pain resulting in decreased ambulation and 75-pound weight loss in the past year. CT scan showed multiple spinal tumors with extensive involvement of L1 along with a hepatic mass measuring 2.8 x 2.1 cm and a complex cystic mass in the pancreatic uncinate process measuring 2.3 x 2.1 cm. The patient underwent an L1 laminectomy and decompression with biopsy. The biopsy showed a poorly differentiated carcinoma with neuroendocrine features. Immunohistochemistry was positive for AE1/AE3, CD56, synaptophysin, chromogranin, diffuse staining for growth hormone and patchy PIT1. This is consistent with metastasis from pituitary carcinoma. Subsequent molecular studies showed MGMT was not methylated. Next-generation sequencing analysis of DNA from this patient has identified clinically significant variants in the ATM and ATRX genes and a clinically significant gain in the CCND2 gene. Following the diagnosis, the patient was treated with capecitabine and temozolominde along with lanreotide. Recent MRI of the spine has shown significant improvement in tumor burden at L1 with reduction of tumor within the spinal canal. Abdominal imaging shows the pancreatic and liver masses to be stable. This case report highlights a rare neoplasm with poorly understood molecular features. 176 An IDH Mutant Glioblastoma with FGFR2-CTNNA3 Fusion Samuel Guzman1, Kyle Hurth1, Anna Mathew1 1Keck Medical Center of the University of Southern California A 40-year-old woman presented with history of nausea, headache, blurry vision, some right-sided weakness and a syncopal episode. MRI brain with and without contrast showed a heterogeneous solid and cystic mass (5.6 x 4.0 x 5.5 cm) in the left parietal lobe with features most concerning for a primary glial neoplasm. H & E stained sections revealed a hypercellular glial neoplasm in a myxoid background. Neoplastic cells were pleomorphic; scattered Touton giant cells and floret-like cells were present. Cells with clear cytoplasm and cells with more eosinophilic cytoplasm were appreciated. In some foci, tumor cells were arranged around blood vessels imparting a perivascular pseudorosette pattern. There were foci of calcification, mitoses including atypical forms and areas of necrosis. Immunohistochemical stains showed the tumor stained with Olig2, GFAP, and IDH1(R132H). ATRX stain was equivocal, with some cells demonstrating loss of nuclear staining. p53 stained numerous tumor cells. Few clusters of tumor cells stained with synaptophysin. Ki-67 was focally as high as 25%. FISH showed chromosome 1p deletion and absence of 19q deletion. Based on the histomorphology and immunohistochemical staining pattern, the findings were consistent with glioblastoma, IDH-mutant, WHO grade IV. Next generation sequencing revealed a pathogenic variation of IDH1, a variant of uncertain significance in ATRX, and two pathogenic fusions: FGFR2-CTNNA3 and FGFR2-MLLT10; MGMT was methylated. As FGFR2-CTNNA3 fusion most commonly occurs in polymorphous low-grade neuroepithelial tumor of the young (PLNTY) (a tumor described as having a predominantly low-grade histologic appearance) a CD34 immunohistochemical stain (positive in PLNTY) was performed and it was negative. There are currently no reports of an FGFR2-CTNNA3 fusion occurring in high-grade or aggressive tumors. In summary, this is a unique glioblastoma, IDH-mutant with FGFR2-CTNNA3 and FGFR2-MLLT10 fusions. 177 Extradural Chordoma of the Thoracic Spine Without Bony Involvement: A Rare Presentation and Case Report Misha Movahed-Ezazi1, Brendan Killory1, Srinivas Mandavilli1, Xianyuan Song1 1Hartford Hospital Introduction: Chordoma is an uncommon, slow growing neoplasm of the bone that typically presents in the skull base and spine. The most prevalent location is the sacrococcygeal region (50-55%) with less than 1% appearing in the thoracic spine. Due to its cell origin of notochord remnants, bony involvement is present in a majority of cases with only several documented cases without osseous involvement, frequently referred to as spinal extra-osseous chordomas or SECs. Within the English literature, there have only been rare reported extra osseous chordomas involving the thoracic spine. Case Presentation: A 63-year-old male with a past medical history of colonic adenocarcinoma and a biopsy proven carcinoid tumor of the lung presented with a large incidental extradural thoracic mass seen on serial imaging for his lung tumor follow-up. He was minimally symptomatic with subtle signs of right-sided myelopathy on examination, but otherwise was neurologically intact. MRI imaging of the spine displayed a 3.4 cm mass along the posterior mediastinum with mild widening of the left T4-T5 neural foramina. Following biopsy diagnosis, the patient underwent surgical excision and proton beam radiation therapy with follow up MRI approximately 12 months after surgery showing posttreatment changes without any evidence of local recurrence. Discussion: Chordomas of the mobile spine account for 10-15% of cases with the thoracic spine being an extremely rare location. Unlike conventional chordomas, it has been shown that this rare presentation of extraosseous lesions tends to have a better prognosis with a lower rate of recurrence and a less aggressive clinical course, especially when en bloc resection is performed. In such cases, chondrosarcoma and metastatic mucinous adenocarcinoma should be included in the differential diagnosis. Conclusions: We report the first documented case of an extradural chordoma without bony involvement presenting in the thoracic spine of a 63-year-old male. 178 FGFR3-LRRC48 Novel Fusion in a Left Temporal Lobe Mass with Pigmented Granules Aliaksandr Aksionau1, Hidehiro Takei1, James Cotelingam1, Arie Perry2, Areli Cuevas Ocampo1 1LSU Health Shreveport; 2UCSF School of Medicine We present a rare, complex-to-diagnose brain lesion with a unique genetic abnormality in a 71-year-old woman who came to the hospital for left frontal headaches, lightheadedness, dizziness, and a recent near-syncopal episode. Preoperative MRI revealed a well-circumscribed left-sided cystic/solid lesion of the posterior temporal lobe (2.0 x 1.8 x 1.3 cm) with focal contrast enhancement. CT scans of the chest, abdomen, and pelvis were normal. Frozen sections demonstrated scant atypical cells with fine pigmented granules. Permanent sections showed a circumscribed proliferation of spindled to epithelioid cells arranged in tight nests with fine intra-cytoplasmic pigmentation in a fine capillary network. The tumor nuclei were ovoid, slightly pleomorphic with occasional prominent nucleoli; however, mitoses or high-grade features were not seen. The tumor cells showed diffuse and strong S100 positivity, rare SOX10 nuclear positivity, equivocal GFAP staining, and negativity for OLIG2. Stains for melanocytic markers were also negative. The Ki-67 proliferation index was estimated at 3-5% focally. Next-Generation Sequencing for BRAF, GNA11, GNAQ, KIT, and NRAS did not reveal mutations. An Expanded Neuro-oncology Gene Panel demonstrated a fusion of FGFR3-LRRC48 genes (exon 17, exon 10), TERT promoter mutation (C228T), and point-based substitutions with the unknown significance of GABRA6, IL4R, TCF12, and TET1. This is a challenging tumor with bland-looking morphology but concerning molecular features including TERT promoter mutation and a fusion involving a fibroblast growth factor receptor, making it suspicious for a high-grade glioma.To our knowledge, FGFR3-LRRC48 fusion has not been described in the medical literature for any known primary or metastatic brain tumor. TERT mutation has been associated with an increased risk of various cancers, including wild-type gliomas, melanomas, atypical meningiomas, among others. We have sent out this case for a second expert neuropathology opinion for final classification. 179 Histologic and DNA Methylation Analysis of a TTF-1 Positive Primary Papillary Epithelial Tumour of the Sella (PPETS) Kiratpreet Dhillon1, Douglas Laske2, Kenneth Aldape3, Zied Abdullaev3, Dario Marotta4, Markku Miettinen3, Mark Curtis1 1Thomas Jefferson University Hospital, Philadelphia, PA; 2Abington Hospital Jefferson Health, Abington PA; 3Center for Cancer Research, National Cancer Institute, Bethesda MD; 4Alabama College of Osteopathic Medicine, Dothan AL Roncaroli and co-investigators (2020) have recently described four cases of a novel sellar TTF-1 epithelial tumor entity “Primary papillary epithelial tumour of the sella (PPETS)”. PPETS and neoplasms previously diagnosed as sellar located ectopic choroid plexus papillomas share histologic characteristics and may represent the same entity. We describe a new case of PPETS and report the tumor’s methylation profile that suggests neither choroid plexus nor pituicyte origin for this sellar epithelial tumor. We present the case of a 59 year old male who presented with dizziness, polyuria, and progressively worsening headaches. MRI revealed a 16 x 13 x 15 mm sellar mass suggestive of pituitary macroadenoma. The mass abutted the optic chiasm. The infundibulum was midline. The surgical resection specimen consisted of a distinctly papillary epithelial mass with focal crowding of papillae and pseudostratification of epithelium. The histologic differential diagnosis included ectopic choroid plexus papilloma, metastatic carcinoma, papillary craniopharyngioma and a pituitary adenoma with papillary features. Immunohistochemical stain for CK7 was strongly positive in all epithelial cells. Strong staining for TTF-1 was present in epithelial cell nuclei. Immunohistochemical stains for GFAP, thyroglobulin, chromogranin, synaptophysin, LH, TSH, FSH, prolactin, GH, ACTH, BRAF(V600E), CK20, Napsin, PAX-8, S-100, and CEA were negative. No nuclear beta-catenin staining was identified. Following these studies, diagnoses of ectopic choroid plexus papilloma and PPETS were considered. DNA methylation profiling analysis was performed and no specific match with high confidence score was obtained ruling out tumor entities including but not limited to choroid plexus papilloma, pituitary adenoma, and craniopharyngioma. A very low confidence score of 0.3 was obtained for pituicytoma, however this value is too low for conclusive diagnosis. The integrated histologic and methylation profile analysis of this tumor supports a diagnosis of PPETS and suggests that PPETS represents a tumor entity distinct from any previously classified CNS neoplasm. 180 Distinguishing Features of Ossifying Fibromas of the Skull: A Diagnostic Mimic of Meningioma Gabrielle Yeaney1, John Reith1 1Cleveland Clinic Diagnosis of benign fibro-osseous lesions of the skull may be a challenge due to overlapping features with intraosseous meningioma. We report an occipital bone tumor in a 13-year-old girl who underwent imaging of the spine for neck pain. X-ray revealed a well-defined lucent lesion in the posterior occiput. CT showed that the lesion was centered in midline occipital calvarium and measured up to 7.5 cm. MRI showed T2 hypointensity and T1 hyperintensity with fluid-fluid level. Excision of the mass revealed a spindle cell neoplasm with abundant interspersed psammomatoid bodies. Immunohistochemistry was positive for EMA, SATB2, SSTR2A and negative for progesterone receptor. Histologic features were most compatible with juvenile psammomatoid ossifying fibroma. We explore the clinical, histologic, and immunohistochemical features of fibro-osseous lesions of the skull, including 10 additional archival ossifying fibromas, to inform which are most useful in distinguishing these tumors from meningioma. 181 Mixed Intramedullary Ependymoma and Hemangioblastoma of the Spinal Cord Teddi Tubre1, John Donahue1 1Department of Pathology and Lab Medicine, RI Hospital/Alpert Medical School While ependymomas and hemangioblastomas are common intramedullary tumors of the spinal cord, mixed tumors are rare. Ependymomas account for approximately 50-60% of all primary intramedullary spinal cord tumors, while hemangioblastomas account for 2-15%. Although both arise sporadically, ependymomas may be associated with NF2 and hemangioblastomas with VHL. Herein, we present a case of an intramedullary spinal cord tumor consisting of juxtaposed ependymoma and hemangioblastoma in a patient with mosaic NF2 schwannomatosis. A 55-year-old male presented with progressive functional and bilateral upper extremity motor decline. MRI exhibited an enhancing intradural intramedullary tumor at the segmental C3-4 level. A posterior cervical laminectomy was performed. Received was a 2.5x1.9x1.5 centimeter red-pink mass with a smooth, glistening surface. Sectioning revealed a circumscribed tan-white nodule embedded within hemorrhagic red-brown tissue. Microscopic examination revealed a contiguous population of two distinct tumor types consisting of a monomorphic population of round-oval nuclei in a perivascular pseudorosette architecture juxtaposed to a dense capillary network admixed with variably sized lipidized stromal cells with vacuolated cytoplasm consistent with ependymoma and hemangioblastoma, respectively. Immunohistochemistry showed the ependymoma component was positive for GFAP and negative for CD31 and Inhibin A, while the hemangioblastoma component was negative for GFAP and positive for CD31 and Inhibin A. Oncopanel somatic mutation testing showed no clinically significant DNA or structural variants; however, both components had monosomy 3. The ependymoma had NF2 two-copy loss, including monosomy 22, likely leading to bi-allelic inactivation. The hemangioblastoma component had NF2 one-copy loss at 22q. To our knowledge, there is the first case report of spinal cord mixed ependymoma and hemangioblastoma with molecular results. While some authors suggest that hemangioblastoma may induce a reactive ependymal proliferation that progresses to neoplasia, our findings suggest the mixed ependymoma and hemangioblastoma components may be a result of a common oncologic factor, specifically NF2. 182 Adult Diffuse Midline Gliomas: A Spectrum of Unusual Cases Kasey Kreutz1, Sonika Dahiya1 1Department of Pathology and Immunology, Washington University School of Medicine Diffuse midline gliomas (DMG) warrant testing for an underlying H3-K27M mutation and H3-mutant DMG are generally more common in the pediatric age group as compared to adults. We recently came across five unusual cases of adult DMG in the thalamus, brainstem and cerebellum, of which four were H3-wildtype. One of them was an IDH1 (R132H) mutant anaplastic astrocytoma from the brainstem of a 64-year-old female. Two cases (from 22 year and 46 year old) were of the midline cerebellar diffuse gliomas that were found to be H3- and IDH-WT but thus far haven't conformed neatly into a distinct diagnostic entity despite applying methylation profiling. A PDGFRA amplified (H3-and IDH-WT) thalamic glioma from a 59-year-old woman. And finally, a H3-K27M mutant diffuse midline (thalamic) glioma in a 30-year-old female who had concurrent ATRX variant on the rebiopsy specimen only (following chemoradiation). These cases demonstrate the heterogeneous molecular landscape of the diffuse midline gliomas (localizing to thalamus, brainstem and cerebellum), and also the utility of ancillary testing for better stratification. However, they also underscore the relative paucity in our understanding of cerebellar diffuse gliomas which are notably quite rare. 183 A Case of POLE Mutation in High-grade Astrocytoma with Variant IDH1 Mutation R132C and Ultramutant Phenotype Benjamin Cho1, Clare Bryce1, Nadejda Tsankova1 1Mount Sinai Hospital Introduction: Pathogenic variants in POLE affect the DNA replication repair protein polymerase ε, resulting in neoplasms with a markedly elevated tumor mutational burden (TMB) and with possible increased susceptibility to immune checkpoint inhibitors. POLE mutations have been associated with ultramutation, high-grade histology, and giant cell features in IDH1-wildtype gliomas, but POLE mutations in IDH-mutant astrocytomas have not been widely reported. Here we present a case of POLE_S459F mutation in an astrocytoma with a variant IDH1 mutation (R132C). Case report: A 23-year-old male presenting with persistent headaches was found to have a 7.9 cm right temporal lobe mass with hemorrhagic components. Upon resection, microscopic exam revealed a densely cellular, extensively necrotic tumor with primitive-appearing cells intermixed with patches of markedly pleomorphic giant cells. By immunohistochemistry (IHC), tumor cells variably expressed GFAP and synaptophysin; showed strong nuclear staining for P53 and MIB-1 in ∼90% of cells; and were negative for IDH1_R132H and H3_K27M. Molecular studies revealed MGMT promoter methylation, microsatellite stability, and a TMB of 265 Muts/Mb. Genomic findings included 44 clinically significant variants, including IDH1_R132C, POLE_S459F, MSH2_R524P, and nonsense mutations in ATRX and TP53, and 191 variants of unknown significance, including MLH1_F753C, MSH2_R711Q, and MSH6_E744D. Mismatch repair (MMR) protein expression appeared intact by IHC. The patient has been referred to genetic counseling for germline testing. Discussion: Although better outcomes are generally expected for IDH-mutant gliomas compared to their IDH-wildtype counterparts, recent studies highlight the importance of molecular context. For example, IDH-mutant astrocytomas with primary MMR deficiencies reportedly have a poor prognosis, and IDH1-wildtype high-grade gliomas with somatic POLE mutations appear to have a relatively favorable prognosis. This case shows that POLE mutations are not limited to IDH-wildtype gliomas. Correlation with germline testing, long-term follow-up, and additional cases will be needed to elucidate the clinical implications of POLE mutations in IDH-mutant astrocytomas. 184 A Novel Quasi-automated Ki67 Labeling Index for Glial Neoplasms Using Batch Digital Image Analysis Sayak Ghatak1, Liam Chen1, William Bell1 1University of Minnesota Background: The tumor proliferation is an important prognostic factor in glial neoplasm. Most frequently assessed by immunohistochemistry, Ki67 labeling index is a surrogate marker for proliferation. Although there is no precise guideline, Ki67 index determined done by visual estimation by a pathologist (analog) or by digital image analysis (DIA). Due to considerable interobserver variation in the analog method, many centers across the world are moving to the use whole slide imaging (WSI) and DIA software as the standardized method. In this abstract, we describe a novel quasi-automated “one click” Ki67 index batch analysis algorithm using digital image-capture and an open source software. Method: We compared the concordance between Ki67 indices calculated by analog and DIA methods for seven cases of glial neoplasms. For DIA method, representative regions of interests (ROI) of hematoxylin (H) and 3,3′-diaminobenzidine (DAB) stained slides are captured at 200x magnification using standard screen capture tools from whole slide images. Using open source software Image-J, the RGB images are deconvoluted to hematoxylin and DAB channels by computing ROI-based deconvolution matrix based on the Beer-Lambert law. After converting the deconvoluted images to binary and segmenting contiguous nuclei, particle detection is done using user-defined thresholds for intensity, size, and circularity. Ki67 index is calculated from the mean particle count from the DAB and hematoxylin channels. The algorithm is then written as a batch image analysis macro on Image-J. At least three ROIs are analyzed for each case. Results: Once the Ki67 hotspots (ROI) are chosen and saved as tiff images in the input folder, the time taken for the batch processing DIA algorithm to calculate Ki67 indices for the seven cases was less than 2 minutes. The mean error of DIA Ki67 index was 7.7%, compared to the gold-standard analog method. 185 De Novo Glioblastoma Multiforme Masqueraded Within a Holohemispheric Dural Meningiomatosis (WHO Grade I): A Staged Resection Nicholas Zacharewski1, Misha Movahed-Ezazi2, Sunil Manjila3, Tapan Mehta2, Xianyuan Song2 1Hartford Hospital/Trinity College; 2Hartford Hospital; 3St. Vincent's Introduction: Intracranial collision tumors are rare clinical presentations of histologically different neoplasms that appear within the same anatomical region of the brain independent of the adjacent cell population. Collision tumors involving meningiomas and other primary brain tumors are reported however in the setting of dural meningiomatosis is not well documented. Collision tumors of various malignancies can evolve from distinctive in-vivo pathways making them fundamentally and etiologically different from “mixed tumors”. Case Presentation: A 72-year-old female with a history of left hemispheric dural based meningiomas (surveillance MR scans over a 10-year period) presented with new-onset significant expressive aphasia and headaches. MRI imaging of the brain revealed multiple small to large broad-based dural, intensely enhancing soft tissue masses in the left hemispheric region, suggestive of multiple meningiomas. Initial embolization of the dural based lesions showed an aberrant branch of anterior cerebral artery supplying the lower pole of tumor suggestive of intra-axial nature; a stage I resection of dural meningiomatosis including the one close to Broca’s area was completed confirming the diagnosis of meningioma (WHO Grade I). Intraoperatively a deeper residual lesion was verified stereotactically and confirmed on postoperative imaging. Emergent MRI showed the residual lesion showing an interval increase in size and worsening perilesional edema. This second lesion underwent a radical microsurgical resection, and proved to be a glioblastoma multiforme (WHO Grade IV). Discussion: Meningiomas and gliomas are two of the most common intracranial lesions presenting as collision tumors. Juxtaposed development of these two lesions is more frequently seen in patients with a history of radiotherapy treatment or phakomatosis. Several case reports have discussed possible theories as to the cause of these collision tumors, yet our understanding remains limited. Conclusion: We present a case of de novo glioblastoma multiforme masqueraded within a holohemispheric dural meningiomatosis (WHO grade 1) in a 72-year-old female. 186 A Rare Case of Orbital Paraganglioma with SDHB Loss: A Case Report Sayak Ghatak1, William Bell1 1University of Minnesota Introduction: Succinate dehydrogenase, the complex II protein in inner mitochondrial membrane, is coded by SDHB and other genes. SDHB is a tumor suppressor, whose loss of function resulting from germline or sporadic mutations, have been identified in gastrointestinal stromal tumors, and rarely in paraganglioma. In this case report abstract, we describe a rare case of paraganglioma with SDHB loss of expression. Case presentation: The patient is a 24-year-old woman who presented with right facial swelling, proptosis, and right-sided decline in vision. Imaging revealed an expansile soft tissue mass centered deep in the right side of face with extension into the posterior orbit, middle cranial fossa, cavernous sinus, posterior ethmoid sinus and sphenoid sinus. Biopsy of the mass was diagnosed as paraganglioma. The patient underwent staged series of four tumor embolizations, followed by surgical resection. Surgical pathologic examination of H&E stained sections of the mass show a neuroendocrine neoplasm with nested architecture and sinusoidal vasculature. Neoplastic cells are polygonal with abundant amphophilic cytoplasm and rounded nuclei. Multiple areas of black embolic material filled blood vessels with surrounding necrotic tumor admixed with hemorrhage were identified. The neoplastic cells are positive for synaptophysin, chromogranin, S100 with loss of expression of SDHB in the paraganglioma. Though initial post-operative imaging showed no residual mass, the patient developed recurrence at the same site within six months of resection. Conclusion: Orbital paraganglioma with SDHB loss is an extremely rare clinical entity. Loss of complex II protein function leads to loss of aerobic respiration in the neoplastic tissue, and dependence on alternate anaerobic energy metabolism. This provides survival benefit to neoplastic cells and leads to pseudohypoxia, activation of HIF1 and VEGF mediated vascular proliferation. Loss of SDHB expression should prompt appropriate molecular testing to identify somatic or germline SDHB mutation and investigation of other syndromic presentations. 187 Case Report: 8-year-old Girl with Meningeal Melanomatosis and NRAS Q61R Mutation in the Setting of Neurocutaneous Melanosis Yelena Fudym1, Haley Amoth1, Noah Brown1, Patricia Robertson1, Sean Ferris1 1University of Michigan We present autopsy findings from an 8-year-old girl with diffuse meningeal melanomatosis in the setting of neurocutaneous melanosis. She presented to the emergency department with sudden right-sided weakness, vomiting and word confusion after 2-3 weeks of headaches. Imaging revealed an area of pachymeningeal and leptomeningeal enhancement along the left superior frontal lobe, and underlying volume loss. Biopsy confirmed leptomeningeal melanomatosis. Next Generation Sequencing (NGS) demonstrated an NRAS Q61R gene mutation. No mutations in GNAQ, GNA11 or KIT were identified. She was treated with the MEK-inhibitor trametinib as well as nivolumab and ipilimumab, with complications including drug-induced diabetic ketoacidosis (DKA) and Type 1 diabetes mellitus (T1DM). She also developed intractable seizures, possible transient ischemic attacks (TIA) and a choreiform movement disorder. With continued decline, she eventually was transitioned to hospice care and passed away. Autopsy was performed and demonstrated: 1) bilateral necrotizing acute bronchopneumonia, 2) meningeal melanomatosis, involving leptomeninges and cortex of brain, and leptomeninges of spinal cord, 3) giant/multiple congenital melanocytic nevi of the skin, and 4) marked islet cell deficiency and scattered lymphocytic infiltrate of the pancreas. She was also noted to have long-standing atrophy of the left cerebellar hemisphere, thought to be of ischemic etiology. NGS of one skin nevus revealed the identical NRAS Q61R mutation identified in her leptomeningeal melanomatosis. This autopsy case is a rare example of childhood diffuse meningeal melanomatosis in the setting of neurocutaneous melanosis, with additional findings of likely checkpoint inhibitor therapy-mediated Type 1 diabetes mellitus, and incidental likely ischemic atrophy of the cerebellum. 188 Primary Intracranial Ewing Sarcoma Maria Pimenova1, Karen Thompson2, Arie Perry3, Jane Uyehara-Lock2 1University of Hawaii; 2University of Hawaii at Manoa; 3University of California, San Francisco Ewing sarcoma family of tumors are a group of small round-cell neoplasms, which include Ewing sarcoma (EWS) of the bone, and Extraosseous Ewing sarcoma (ESS). Ewing sarcoma, presumed to be neuroectodermal in origin, most often occurs in the bone and soft tissues of children and young adults. The intracranial Extraosseous Ewing sarcoma (CNS-ESS) is extremely rare and is often misdiagnosed as a central nervous system (CNS) embryonal tumor or as other primary intracranial neoplasms. We report a case of a 16-year-old girl with a right ventricular focally cystic mass. Microscopic examination showed a primitive small blue cell tumor with vague rosetting, focal areas of hemorrhage, and foci of geographic necrosis. A CD99 immunostain showed membranous positivity with EWS-FLI1 fusion detectopm confirming the diagnosis of CNS-EES. Although CNS-EES may look similar to CNS embryonal tumors, CNS-EES differ in histogenesis, molecular characteristics, and clinical behavior. Demonstration of a characteristic translocation by molecular studies differentiates CNS-EES from CNS embryonal tumors and help oncologists make informed decisions regarding therapy. Long-term disease-free survival is possible with surgical resection combined with an appropriate therapeutic regimen including chemoradiation therapy. 189 Cerebellar Intraparenchymal Schwannoma Christine Fuller1, Kavya Mirchia2, Daniel Zaccarini1, Satish Krishnamurthy3, Ruham Alshiekh Nasany4 1SUNY Upstate Medical University, Department of Pathology; 2SUNY Upstate Medical University, Department of Radiology; 3SUNY Upstate Medical University, Department of Neurosurgery; 4SUNY Upstate Medical University, Department of Hematology Oncology Schwannomas of the central nervous system (CNS) frequently arise within the posterior fossa, most often involving cranial nerves, especially the vestibular or trigeminal. Herein we present a unique example of a cerebellar intraparenchymal schwannoma arising in an adult with multiple additional lesions elsewhere within the spine and pelvis. A 30 year-old woman presented with several month history of worsening severe neck pain and headache refractory to analgesics and eventually, developed somnolence, nausea, and vomiting. Neuroimaging demonstrated a heterogeneously enhancing large lobulated complex solid and cystic mass in the left cerebellum abutting the tentorium and compressing the adjacent pons with surrounding vasogenic edema. There was mass effect on fourth ventricle causing triventricular hydrocephalus. A separate small solid enhancing falcine lesion was presumed to represent a meningioma. At surgery, the cerebellar lesion was found well demarcated from the surrounding brain, with focal attachment to the tentorium. Tumor did not grossly appear to involve cranial nerves, and formal audiology examination was normal. Additional imaging documented multiple nodular enhancing lesions in the thecal sac at L4-L5 and within the presacral/pelvic soft tissues. Examination of tissue from the cerebellar tumor resection and one pelvic mass (needle biopsy) indicated both lesions represented schwannomas. Immunostain targeting INI1 showed a mosaic pattern of nuclear positivity. Targeted genetic testing performed on blood identified variants of uncertain significance in LZTR1 and SMARCB1 genes; there were no NF2 alterations detected. This case emphasizes that schwannomas may on occasion arise within the CNS independent of cranial nerves, potentially mimicking a wide variety of dural-based or intraparenchymal lesions on neuroimaging. 190 A Case Report of H3.3 G34-mutant, IDH-wild type Diffuse Hemispheric Glioma Presents as PNET like Morphology Purvi Patel1, Jianying Zeng1 1SUNY Downstate Medical Center, Brooklyn, NY Approach to the diagnosis of pediatric gliomas using morphology and molecular diagnostic techniques help define the high-grade pediatric type gliomas. Recurrent mutations in H3F3A that encode the histone 3 variant H3.3, lead to amino acid substitutions including K27M and G34R/V-which are observed in many high-grade gliomas of children and young adults. Herein, we report a case of 25 years old female with a clinical history of focal neurological signs presents to the emergency department for 10 days of diplopia. Brain MRI shows an infiltrative expansile mass in the right parietal lobe with mild enhancement and FLAIR/T2/DWI hyperintensity. Brain biopsy and resection specimen reveal typical areas of infiltrating glioma with perineuronal satellitosis and highly cellular areas of primitive-looking cells with active mitosis. Immunohistochemical studies show these primitive cells are strongly positive for synaptophysin, focally positive for GFAP. They are diffusely positive for P53; while immuno- negative for IDH1 R132H. IDH 1&2 mutation analysis is also negative and FISH test for1p19q co-deletions negative for deletion of the short arm of chromosome 1, while deletion of the long arm of chromosome 19 was observed in 19% of cells. The MGMT promoter methylation is present. The next Gene Sequence reveals H3F3A G35R (G34R by mature peptide numbering) mutation, with associated ATRX, TP53, PDGFRA, CDKN2A mutations. Diffuse hemispheric glioma, H3.3 G34-mutant, is recommended by cIMPACT-NOW as a novel entity and corresponding to WHO grade IV. It is distinct from the established types of IDH-mutant and IDH-wild type gliomas, as well as from the H3 K27M-mutant diffuse midline gliomas, especially in regards to survival prognosis for the current standard of care. Being aware of the morphological heterogeneity of this entity, especially rarely presenting as primitive neoplasm in a young patient, should prompt us to actively approach for molecular techniques. 191 Gliosarcoma Presenting with Extracranial Metastasis: Molecular Features of an Institutional Cohort of Sarcomatous Gliomas Wen Zhong1, Thomas Pearce1 1Division of Neuropathology, University of Pittsburgh Medical Center Gliosarcoma, an uncommon morphologic variant of glioblastoma, is characterized by a biphasic growth pattern of admixed glial and sarcomatous elements. The two cell populations arise from a common monoclonal progenitor, but show histomorphologic and immunophenotypic differences, and the sarcomatous component has a greater propensity for extracranial metastasis. Here, we present a series of recently diagnosed gliosarcomas that demonstrate some of the unusual features these neoplasms can exhibit. Two of the cases presented with discrete multifocal brain lesions with sharp borders and no intervening signal change on magnetic resonance imaging, leading to a strong radiologic suspicion for metastatic origin. One of these additionally was found to have a concurrent mediastinal mass, further supporting a probable extracranial origin. In both cases, biopsy of the brain lesion showed gliosarcoma with a robust macrophage-rich inflammatory infiltrate. The mediastinal mass was also biopsied, and was histologically and molecularly identical to the sarcomatous component of the corresponding brain lesion, leading to a diagnosis of gliosarcoma with extracranial metastasis at presentation. A third case showed point mutations in EGFR (p.G598V) and BRAF (p.V600E) with identical allelic frequencies; the gliomatous and sarcomatous components showed inverse immunostaining patterns for EGFR and mutant BRAF, suggesting that while the two cell populations share a common genetic background, expression-level differences may explain the different biologic behavior of the two components. To place these recent tumors in context, we also present the spectrum of molecular findings from 32 cases of gliosarcoma diagnosed at our institution over the past 12 years which underwent next generation sequencing. Copy number losses corresponding to CDKN2A/B and PTEN were the most common alterations, while copy number gains/amplifications were uncommon. Regarding mutations, the TERT promoter and TP53 were most common, while PIK3CA, BRAF V600E and RB1 mutations were only seen in rare cases. 192 Myxoid Glioneuronal Tumor, PDGFRA p.K385L-mutant, Arising in Midbrain Tectum with Multifocal CSF Dissemination BK Kleinschmidt-DeMasters1, Thomas Borges1, Ahmed Gilani1 1University of Colorado Health Sciences Center, Aurora, CO Myxoid glioneuronal tumor is a recently codified tumor with PDGFRA p.K385 mutation thus far epicentered/arising only in the septum pellucidum, septal nuclei, corpus callosum and lateral ventricle. Histological features are similar to rosette forming glioneuronal tumor (RGNT) or dysembryoplastic neuroepithelial tumor (DNET) but, unlike these two entities, tumors lack PIK3CA/PIK3R1 alterations or BRAF/ FGFR1 mutations, respectively. We report the first genetically verified example arising in the midbrain tectum, with additional unusual features of enhancement as well as multifocal infratentorial and spinal cord cerebrospinal fluid (CSF) dissemination at diagnosis. A 41-year-old female developed headache and neck pain seven months prior to biopsy; progressive symptoms prompted her to seek medical attention. Neuroimaging demonstrated a complex exophytic lesion in midbrain tectum (Figure a), with leptomeningeal cerebellar folial enhancement (Figure b), as well as enhancing nodular lesions in posterior fossa, cervical and thoracic leptomeninges, and L5 cord nerve root. Histology showed typical DNET-like features, with uniform small round oligodendroglial-like cells with delicate chromatin, embedded with copious mucin. No floating neurons or rosettes were identified on H&E or synaptophysin immunostaining; tumor cells manifested the characteristic scant GFAP+ cytoplasm, strong nuclear OLIG2, and absent mitotic activity. Very focal hemosiderin pigment and small numbers of eosinophilic granular bodies were present, a finding described in the minority of examples in the report by Chiang (Neuro-Oncology 21(6), 800–808, 2019). Mutational testing demonstrated PDGFRA p.K385L as well as a NOTCH1 p.T1344M. Similar to RGNT and DNET, originally reported in 4th ventricle and temporal lobe seizure specimens, respectively, but both subsequently identified elsewhere, we now report a myxoid glioneuronal tumor arising in a mesencephalic location. Additional unusual features are the widespread CSF dissemination at presentation, including to spine. © 2021 American Association of Neuropathologists, Inc. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
TI - American Association of Neuropathologists, Inc. Abstracts of the 97th Annual Meeting June 10-13, 2021 St. Louis, Missouri
JO - Journal of Neuropathology & Experimental Neurology
DO - 10.1093/jnen/nlab042
DA - 2021-06-04
UR - https://www.deepdyve.com/lp/oxford-university-press/american-association-of-neuropathologists-inc-abstracts-of-the-97th-9gd7P1C7PR
SP - 558
EP - 607
VL - 80
IS - 6
DP - DeepDyve
ER -