Multicenter Investigation of Channel-Based Subcortical Trans-Sulcal Exoscopic Resection of Metastatic Brain Tumors: A Retrospective Case Series

Multicenter Investigation of Channel-Based Subcortical Trans-Sulcal Exoscopic Resection of... Abstract BACKGROUND Recent advancements have aimed to optimize visualization and minimize insult to healthy cortical and subcortical tissue through the use of tubular-based retractors. OBJECTIVE To investigate outcomes following resection of cerebral metastases using an integrated tubular retraction system with an exoscope and neuronavigation. METHODS A multicenter retrospective analysis of surgical outcomes in consecutive patients who underwent resection of a brain metastasis using a tubular retraction system and exoscope was performed. RESULTS Twenty-five patients were included, with a mean age of 61 yr (24-81 yr). Primary sources included lung (n = 13), breast (n = 3), renal cell (n = 3), and other (n = 6). Locations were frontal (n = 5), parietal (n = 8), cerebellar (n = 8), occipital (n = 3), and splenium (n = 1). Most lesions had a maximum diameter > 3.0 cm (n = 20) and a tumor depth > 4 cm (n = 14). Conversion to open (microscopic) craniotomy was not required in any case. Gross total resection was achieved in 20 cases (80.0%) and subtotal resection in 5 cases (20.0%). Median hospital stay was 2 d (1-12 d). All patients underwent postoperative radiation therapy. Perioperative complications developed in 1 patient (4.0%; hemiparesis and subsequent deep vein thrombosis). At 3-mo follow-up, no mortalities were observed, 19 patients (76.0%) demonstrated neurological improvements, 5 patients (20.0%) had a stable neurological exam, and 1 patient (4.0%) had a neurological decline. CONCLUSION Utilization of a channel-based, navigable retractor and exoscope is a feasible option for surgical resection of metastatic brain lesions. Deep-seated lesions, Neuro-oncology, Minimally invasive surgery, Tubular retractor, Exoscope, Intraoperative navigation, Surgical technique Recent advancements in cranial neurosurgery aim to optimize visualization and minimize insult to healthy brain tissue through the use of tubular or channel-based retractors. To date, many neurosurgical techniques have been performed with the aid of the microscope, endoscope, and exoscope using tubular retraction systems.1-3 While the surgical microscope provides direct binocular and stereoscopic vision, limitations can include depth of field, illumination, and ergonomics when working in deep corridors. On the other hand, endoscopic visualization offers improved panoramic visualization and illumination, but must be inserted into the surgical cavity and may pose a challenge when working within a limited surgical corridor. To overcome aforementioned obstacles, the use of an exoscope has been proposed, given that it has a wider focal distance and volume of focus, while providing high-quality views of the surgical field on a monitor.1,4 Thus, there has been a growing interest in investigating the use of the exoscope with modern tubular retraction systems for accessing subcortical brain lesions.1,2,4-6 The first reports of tubular retraction systems were introduced over 30 yr ago for resection of deep brain lesions,7-9 but because of the requirement for stereotactic frames, limited visualization, and availability of adequate surgical instruments, the widespread adoption of the approach remained hindered.1,3,4 More recently, many shortcomings associated with prior tubular retractor systems were overcome with the integration of new channel designs and optical technology that allow bimanual surgery through a minimally invasive corridor while using a frameless navigation system. Tubular retractors with microscopes or endoscopes have previously been shown to provide safe access for the resection of deep-seated brain lesions.10,11 Visualization may be further enhanced with an exoscope, as they have been shown to be safe and effective in hematoma evacuation,5,6 brain tumors,12 and in the resection of intra- or periventricular lesions.2 The safety and feasibility in the resection of metastatic brain tumors with an exoscopic tubular retractor system remains unclear. Brain metastases are the most common central nervous system neoplasms, and their incidence continues to rise with improvements in diagnostic modalities and systemic treatments.13 Treatment options include radiosurgery or whole brain radiation therapy, laser-induced thermal therapy (LITT), or traditional open craniotomy for surgical resection.14-19 Prior class I studies have shown greater survival and functional independence with surgical resection of solitary brain metastasis followed by radiation therapy vs those treated with radiation therapy alone.16-18 However, no preferred treatment option exists for larger, subcortical deep-seated metastases with mass effect and surrounding edema. These lesions may not be ideal candidates for radiosurgery alone due to large tumor volumes with significant surrounding edema and long-term steroid dependence. Objectives The authors sought to determine the safety and feasibility in the use of an integrated tubular retractor with an exoscope for resecting carefully selected metastatic brain lesions. To this end, we retrospectively analyzed surgical outcomes from utilization of a tubular retraction system with an exoscope for the resection of metastatic brain tumors across 6 institutions. METHODS Study design and Setting This is a retrospective analysis across 6 centers in the USA from 2012 to 2017. The database contained all patients who underwent cranial surgery with the use of an integrated tubular retraction system (BrainPath, NICO Corporation, Indianapolis, Indiana) and exoscope. Written informed consent for surgical resection was obtained as per regular protocol. Institutional review board and ethics committee approval was obtained for retrospective analysis. This article adhered to the reporting guideline of Strengthening the Reporting of Observational studies in Epidemiology.20 Participants Indications for surgical resection included patients that were symptomatic from mass effect and for confirmation of the unknown diagnosis. Patients with pathology-proven metastatic brain tumors measuring ≥ 2 cm at the widest diameter with at least 3-mo follow-up data were included. All patients underwent an oncologic evaluation to evaluate their systemic tumor burden and general medical health. Only patients with solitary metastatic brain lesions were included in this study. Patients with previous metastatic brain tumor resections, poor Karnofsky Performance Status score (<70), uncontrolled systemic disease, and/or leptomeningeal disease were excluded from the analysis. Study Size and Bias Limited data were available for a power analysis due to the novelty of this investigation; therefore, the study design was limited to a pilot study. To limit bias, consecutive patients from multiple institutions were included. Variables and Data Sources/Measurement The demographics, clinical, and imaging data of all patients were collected and entered into a secured spreadsheet. Data on the metastatic lesions, including location, maximal diameter (2-3 cm or >3 cm), depth (<2 cm, 2-4 cm, or >4 cm), final pathologic diagnosis, and intraoperative tumor core and capsule characteristics (surgeon's perspective of soft vs firm) were collected. Data on maximal diameter and depth were stratified based on prior reports1,5,10,12 and hypothesized impact on surgical outcome with the use of the exoscopic-tubular retractor technique. Tumor resection was analyzed based on postoperative magnetic resonance imaging (MRI) and was defined as gross-total resection (GTR) or subtotal resection (STR). Additional outcomes including hospital stay, perioperative complications, immediate and 90-d neurological outcomes (either improved, stable, or worse) were collected. Mortality was classified as postoperative deaths within 30 d of surgery or otherwise as related to systemic disease (90-d mortality). Statistical Methods Statistical significance in potential associations with tumor characteristics, size, and depth on the extent of resection were analyzed with SPSS v24 (IBM, Armonk, New York). In select cases, missing data were obtained from the electronic medical record. No patients were lost to follow-up. Exoscopic Channel-Based Protocol Frameless stereotactic navigation was utilized to plan a surgical corridor. In select cases, diffusion tensor imaging was used to plan an approach around critical subcortical white matter tracts. The BrainPath (NICO Corporation) surgical port was used in all cases, and comprises an inner obturator and an outer sheath. The navigation probe was placed inside the obturator to guide the planned trajectory and cannulation via a trans-sulcal approach. Operative visualization was obtained with an exoscope (Karl Storz Endoscopy, Tuttlingen, Germany or Synaptive Medical, Toronto, Canada)1,4 which was secured to a pneumatic holder (Karl Storz Endoscopy) for mobilization. Operative Technique All cases were performed under general endotracheal anesthesia except for 2 cases, which were performed with anesthesia for awake craniotomies. A small craniotomy overlying the planned trans-sulcal trajectory was performed. A small (≥13 mm) durotomy and arachnoid opening was made, and the port was introduced under navigation guidance until the obturator tip reached the planned target (Video, Supplemental Digital Content). The inner obturator was then removed, and the outer sheath was secured to a standard surgical retractor. Tumor resection was performed using standard bimanual microsurgical methods, a side-cutting aspirator (Myriad from NICO Corporation), and/or ultrasonic aspirating instruments as needed.2,21 In general, hemostasis was successfully acquired through standard microsurgical techniques, with bayoneted bipolar forceps and the application of standard hemostatic agents. RESULTS Patient Characteristics Twenty-five patients (Table) with metastatic lesions were included in the analysis (12 male, 13 female). The mean age at surgical resection was 61 yr (range 24-81 yr). Primary cancer sources included lung (n = 13), breast (n = 3), liver (n = 2), prostate (n = 1), renal cell (n = 3), colon (n = 2), and salivary gland (n = 1). They were located in parietal (n = 8), cerebellar (n = 8), frontal (n = 5), occipital (n = 3), and splenium (n = 1) regions. Twenty lesions had a maximum diameter of >3.0 cm and 5 lesions were between 2.0 and 3.0 cm. Tumor depth was >4 cm in 14 patients, 2.0 and 4.0 cm in 5 patients, and <2 cm in 6 patients. TABLE. Summary of patient data included in this study Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 DVT, deep vein thrombosis; GTR, gross total resection; L, indicates left; Path, pathology; POD, postoperative day; R, indicates Right; STR, subtotal resection. View Large TABLE. Summary of patient data included in this study Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 DVT, deep vein thrombosis; GTR, gross total resection; L, indicates left; Path, pathology; POD, postoperative day; R, indicates Right; STR, subtotal resection. View Large Surgical Outcomes Intraoperative conversion to a larger or open craniotomy or the use of a microscope was not required in any case. A transsulcal transcortical approach was used in all cases. A posterior transsulcal transcortical approach was utilized in the case of the lesion involving the splenium. Thirteen of the metastatic lesions were found to have a firm core and capsule, 7 were found to have a soft core and capsule, and 5 were found to have a soft core with a firm capsule. GTR was achieved in 20 cases (80.0%) and STR in 5 cases (20.0%). All cases with residual tumor had a firm capsule. The median postoperative hospital stay was 2 d (average = 3.5, range = 1-12 d). Complications occurred in 1 patient (4.0%), which included postoperative hemiparesis and subsequent deep vein thrombosis. This patient (Table: case no. 13) had a 3.5-cm lesion (measured at widest diameter) with a firm capsule and core located in the deep left frontal lobe adjacent to the posterior internal capsule. During surgical resection of the medial portion of this lesion, reductions in right-sided motor-evoked potentials were noted and the resection was aborted. The patient had postoperative hemiparesis that gradually resolved. The patient underwent gamma knife stereotactic radiosurgery (Elekta AB, Stockholm, Sweden) for the residual tumor and remained alive without progression of the lesion at 31-mo follow-up. No patients were lost to follow-up. At 3-mo follow-up, 19 patients (76.0%) demonstrated improvements in their neurological exam, 5 patients (20.0%) had a stable neurological exam, and 1 patient (4.0%) demonstrated new neurological deficits. All patients received postoperative radiosurgery to the resection cavity, except 1 patient (Table: case no. 18) who received whole brain radiation therapy at an outside facility. No mortalities were observed at 3-mo follow-up evaluations. Illustrative Case A 78-yr-old man with a past medical history of stage IV colon adenocarcinoma (Table: case no. 4) presented with complaints of speech difficulty, right-sided apraxia, and visual deficits (Video, Supplemental Digital Content). MRI showed a heterogeneously enhancing 2 cm mass within the left parietal periventricular white matter with a significant amount of perilesional vasogenic edema (Figure 1). Given the patient's neurological symptoms and location of lesion, surgical resection followed by adjuvant radiation was recommended. Under navigational guidance (Figure 2), a 3-cm craniotomy was performed on the left parieto-occipital region and a dural opening was made. A sulcus was identified for the entry point with navigation and dissected open (Figures 3-4). A 50 mm BrainPath retractor (NICO Corp) was inserted into the dissected sulcus and cannulated to a depth of 45 mm using navigation guidance, and then secured. The obturator was then removed and the exoscope was used to visualize and resect the tumor and the distal end of the port (Figure 5). The tumor was removed using a combination of suction, piecemeal resection, and side-cutting aspirator (NICO Myriad) until an intraoperative GTR was achieved. There were no changes in somatosensory or motor-evoked potential monitoring. Following meticulous hemostasis, the BrainPath tube was gently withdrawn, and hemostasis was achieved along the tract using Surgicel (Figure 6). Immediate postoperative imaging confirmed GTR (Figure 7). The final pathology diagnosis was consistent with metastatic colon adenocarcinoma. There were no complications associated with the surgery, and the patient was discharged home on postoperative day 2. He subsequently received adjuvant radiosurgery to the resection cavity followed by chemotherapy. At 3-mo follow-up, the patient's presenting neurological symptoms had resolved. MRI at that time demonstrated no evidence of residual or recurrent tumor. FIGURE 1. View largeDownload slide Example of preoperative imaging of deep-seated metastatic lesion. (Left) Preoperative T1-weighted MRI and (center) T1-weighted postcontrast MRI demonstrated 2.6 × 2.5 cm lobular heterogeneous enhancing lesion within the left parietal periatrial white matter, consistent with a metastatic lesion. (Right) FLAIR MRI demonstrated moderate to large amount of adjacent vasogenic edema and foci of hemorrhage within the lesion (seen on other sequences). FIGURE 1. View largeDownload slide Example of preoperative imaging of deep-seated metastatic lesion. (Left) Preoperative T1-weighted MRI and (center) T1-weighted postcontrast MRI demonstrated 2.6 × 2.5 cm lobular heterogeneous enhancing lesion within the left parietal periatrial white matter, consistent with a metastatic lesion. (Right) FLAIR MRI demonstrated moderate to large amount of adjacent vasogenic edema and foci of hemorrhage within the lesion (seen on other sequences). FIGURE 2. View largeDownload slide Navigation-guided trajectory. Frameless stereotactic navigation was utilized to plan and execute a surgical corridor based on assessing sagittal, coronal, and axial images. FIGURE 2. View largeDownload slide Navigation-guided trajectory. Frameless stereotactic navigation was utilized to plan and execute a surgical corridor based on assessing sagittal, coronal, and axial images. FIGURE 3. View largeDownload slide Identifying the appropriate sulcus is for BrainPath (NICO Corp) retractor entry. FIGURE 3. View largeDownload slide Identifying the appropriate sulcus is for BrainPath (NICO Corp) retractor entry. FIGURE 4. View largeDownload slide Opening the sulcus to introduce the tubular retractor. FIGURE 4. View largeDownload slide Opening the sulcus to introduce the tubular retractor. FIGURE 5. View largeDownload slide Demonstrating the view of the metastatic lesion with the tubular retractor and exoscope. FIGURE 5. View largeDownload slide Demonstrating the view of the metastatic lesion with the tubular retractor and exoscope. FIGURE 6. View largeDownload slide Showing the sulcal entry point after the tubular retractor was withdrawn and hemostasis was achieved along the tract using Surgicel. FIGURE 6. View largeDownload slide Showing the sulcal entry point after the tubular retractor was withdrawn and hemostasis was achieved along the tract using Surgicel. FIGURE 7. View largeDownload slide Example of postoperative imaging of deep-seated metastatic lesion. (Left) Immediate postoperative T1-weighted MRI and T1-weighted postcontrast MRI (center) demonstrated GTR of left parietal mass and decreased (right) signal on FLAIR. FIGURE 7. View largeDownload slide Example of postoperative imaging of deep-seated metastatic lesion. (Left) Immediate postoperative T1-weighted MRI and T1-weighted postcontrast MRI (center) demonstrated GTR of left parietal mass and decreased (right) signal on FLAIR. DISCUSSION Brain metastases are the most common intracranial neoplasms, and their reported incidence continues to increase.13 When used in combination with radiation-based treatments, surgical resection has been advocated as a primary option for patients with brain metastasis.13,18,22 The current multi-institutional consecutive case series demonstrated that utilization of a navigable tubular retractor and exoscope appears to be safe and feasible surgical option for trans-sulcal resection of carefully selected metastatic brain lesions. The resection of single, symptomatic brain metastases in conjunction with radiation-based treatments has previously been shown to demonstrate an overall survival benefit in class I studies.16,17 Additional benefits with the current approach may include shorter hospital length of stay, safer tissue acquisition, while optimizing target volume for radiosurgery. Multiple treatment options are available and should be carefully considered for patients with brain metastases.18,23-25 Most patients with brain metastases can be treated with radiation-based treatments. Larger (>2.5 cm), symptomatic, isolated, and surgically accessible metastases should be given strong consideration for surgical resection.16,17 For larger tumors that are not ideal candidates for radiosurgery (larger tumor volumes, surrounding vasogenic edema, and/or long-term corticosteroid dependence), options can include surgical resection or LITT.18,26 Trans-sulcal channel-based approaches with adjuvant radiosurgery may also be a viable option. Acquiring GTR of brain metastases has been shown to improve patient survival in retrospective comparative studies.27,28 Resection of metastatic lesions through the port, even those prone to hemorrhage, did not present as a major obstacle for resection. While GTR was obtained in most cases, STRs occurred with deep-seated lesions located nearby eloquent regions. This obstacle was encountered when the metastatic lesion involved the corticospinal tract adjacent to the posterior internal capsule. Intraoperative motor-evoked potential signals declined, and the patient developed postoperative right-sided hemiparesis (Table: case no. 14). This case may have benefited from concurrent intraoperative subcortical motor mapping, but this was not feasible with the retractor system. Tumors were resected in a piecemeal fashion, as an en bloc resection was not feasible with this approach. Previous investigations have suggested that piecemeal resection of single metastatic brain lesions may increase the risk for leptomeningeal disease and local recurrence when compared to en bloc resection.29,30 However, postoperative radiotherapy was performed in all cases included in their investigation, and it is unclear if the benefit of en bloc resection would still be present with modern postoperative radiation treatment options. The current study is limited by a short follow-up, but none of the cases included in the current study had signs of leptomeningeal disease and almost all patients were followed up with postoperative stereotactic radiosurgery. When lesions are adjacent to eloquent motor or speech regions, resection through a piecemeal fashion of tumors nearby eloquent regions may be preferred in an effort to avoid postoperative deficits. In these cases, STR with the goal of optimizing an adaptive target for subsequent stereotactic radiosurgery may be the preferred option. On the other hand, the resection of metastatic tumors nearby eloquent regions through a piecemeal fashion has not been shown to be safer in retrospective comparative case studies.30 The tumor's consistency (ie, firmness) is an important factor to be aware of, as it may become a surgical obstacle. Although a statistical association with the consistency of the metastatic tumor was not observed due to a low-powered investigation, it was felt that a softer tumor consistency was more amenable for channel-based resection. This is in line with reports that the soft consistency of intracerebral hematomas likely facilitates channel-based evacuation.5,6 Predicting the consistency of tumors, including adhesion to surrounding brain parenchyma, could provide valuable information for preoperative planning and predicting the extent of resection.31,32 Unfortunately, the current study did not have a large enough sample size to evaluate for significant correlations with tumor consistency. New magnetic resonance elastography based techniques have been shown to predict the degree of meningioma to brain parenchyma adhesions,32 and the investigation into the integration of these techniques may prove useful. The size of the tumor has also previously been reported to be less important than the consistency and anatomical location.2,10 Eliyas et al2 retrospectively analyzed 20 patients that underwent surgical resection with a tubular retractor and exoscope for lesions with average depths of 4.37 cm from the cortex. The authors achieved GTR in 85% of cases, and observed STRs with lesions that invaded eloquent regions. GTR rates in our case series were similar to patients treated surgically for metastatic lesions with high functional scores.22 Although a direct comparison cannot be drawn, median postoperative hospital stay appeared to be lower than prior reports (2 vs 6-7 d).13,22 Hospital stay may also vary due to required additional diagnostic evaluations/consultations or length of inpatient rehabilitation. The use of tubular retractors with an exoscope has previously shown promising results with evacuation of intracerebral hemorrhages and tumors.2,5,6,12 Recently, Day12 reported their experience with using this technique, and observed GTR in 19 of 20 metastatic brain lesions, 1 mortality due to pulmonary complications in a patient with nonsmall cell lung carcinoma and 1 postoperative hemorrhage that did not require surgical evacuation. The majority of their complications occurred in patients with gliomas and details on neurological outcomes were not reported. Bander et al33 retrospectively analyzed postoperative magnetic resonance fluid-attenuated inversion-recovery (FLAIR) hyperintensity and diffusion-weighted imaging of 20 patients that underwent resection of a deep-seated brain lesion with a METRx tubular retractor system with a microscope or endoscope. The authors achieved GTR in 75%, near-total resection in 10%, and STR in 15% of patients. Traditional retractors were found to have more postoperative restricted diffusion, but the results were not significant. This may be due to low power or the lack of objective volumetric analysis. The use of an endoscope with modern tubular retractors has previously been shown to result in higher rates of STRs.10,11 Limitations This study is limited by its retrospective study design and additional information on adjuvant therapies and long-term outcomes (particularly on the incidence of leptomeningeal disease and local recurrence). The study is also confounded by selection bias for patients selected for this technique. The indication used for this technique was for large (>2 cm at the widest diameter) presumed metastatic lesions with peritumoral edema or mass effect making them suboptimal to manage with radiosurgery alone. The number of patients meeting these indications was low; therefore, further investigations are needed to help delineate which patients would benefit the most with tubular surgical resection of deep-seated lesions over open microsurgical surgery. Investigations on the functional status of patient, tumor burden, number of brain lesions, and its impact on predicting prognosis and survival is currently underway. Although this is a low-powered study with short follow-up, the feasibility and safety of this technique have both been highlighted during this time period. CONCLUSION In our initial multi-institutional experience, we demonstrated that the utilization of a navigable channel retractor and exoscope appears to be safe and feasible for surgical resection of subcortical metastatic brain lesions. Disclosures US Food and Drug Administration-approved access system (BrainPath, NICO Corporation, Indianapolis, Indiana). Dr Pradilla is Principal Investigator for the ENRICH trial (Early Minimally Invasive Removal of ICH), funded by NICO corporation. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Mamelak AN , Nobuto T , Berci G . Initial clinical experience with a high-definition exoscope system for microneurosurgery . Neurosurgery . 2010 ; 67 ( 2 ): 476 - 483 . Google Scholar CrossRef Search ADS PubMed 2. Eliyas JK , Glynn R , Kulwin CG et al. Minimally invasive transsulcal resection of intraventricular and periventricular lesions through a tubular retractor system: multicentric experience and results . World Neurosurg . 2016 ; 90 : 556 - 564 . Google Scholar CrossRef Search ADS PubMed 3. Greenfield JP , Cobb WS , Tsouris AJ , Schwartz TH . Stereotactic minimally invasive tubular retractor system for deep brain lesions . Neurosurgery . 2008 ; 63 ( 4 Suppl 2 ): 334 - 339 ; discussion 339-340 . Google Scholar PubMed 4. Mamelak AN , Danielpour M , Black KL , Hagike M , Berci G . A high-definition exoscope system for neurosurgery and other microsurgical disciplines: preliminary report . Surg Innov . 2008 ; 15 ( 1 ): 38 - 46 . Google Scholar CrossRef Search ADS PubMed 5. Labib MA , Shah M , Kassam AB et al. The safety and feasibility of image-guided BrainPath-mediated transsulcul hematoma evacuation . Neurosurgery . 2017 ; 80 ( 4 ): 515 - 524 . Google Scholar PubMed 6. Bauer AM , Rasmussen PA , Bain MD . Initial single-center technical experience with the BrainPath system for acute intracerebral hemorrhage evacuation . Oper Neurosurg . 2017 ; 13 ( 1 ): 69 - 76 . 7. Kelly PJ , Kall BA , Goerss SJ . Computer-interactive stereotactic resection of deep-seated and centrally located intraaxial brain lesions . Appl Neurophysiol . 1987 ; 50 ( 1-6 ): 107 - 113 . Google Scholar PubMed 8. Otsuki T , Jokura H , Yoshimoto T . Stereotactic guiding tube for open-system endoscopy: a new approach for the stereotactic endoscopic resection of intra-axial brain tumors . Neurosurgery . 1990 ; 27 ( 2 ): 326 - 330 . Google Scholar CrossRef Search ADS PubMed 9. Cabbell KL , Ross DA . Stereotactic microsurgical craniotomy for the treatment of third ventricular colloid cysts . Neurosurgery . 1996 ; 38 ( 2 ): 301 - 307 . Google Scholar CrossRef Search ADS PubMed 10. Hong CS , Prevedello DM , Elder JB . Comparison of endoscope- versus microscope-assisted resection of deep-seated intracranial lesions using a minimally invasive port retractor system . J Neurosurg . 2016 ; 124 ( 3 ): 799 - 810 . Google Scholar CrossRef Search ADS PubMed 11. Kassam AB , Engh JA , Mintz AH , Prevedello DM . Completely endoscopic resection of intraparenchymal brain tumors . J Neurosurg . 2009 ; 110 ( 1 ): 116 - 123 . Google Scholar CrossRef Search ADS PubMed 12. Day JD. Transsulcal parafascicular surgery using Brain Path® for subcortical lesions . Neurosurgery . 2017 ; 64 ( CN_suppl_1 ): 151 - 156 . Google Scholar CrossRef Search ADS PubMed 13. D’Andrea G , Palombi L , Minniti G , Pesce A , Marchetti P . Brain metastases: surgical treatment and overall survival . World Neurosurg . 2017 ; 97 : 169 - 177 . Google Scholar CrossRef Search ADS PubMed 14. Andrews DW , Scott CB , Sperduto PW et al. Whole brain radiation therapy with or without stereotactic radiosurgery boost for patients with one to three brain metastases: phase III results of the RTOG 9508 randomised trial . Lancet North Am Ed . 2004 ; 363 ( 9422 ): 1665 - 1672 . Google Scholar CrossRef Search ADS 15. Aoyama H , Shirato H , Tago M et al. Stereotactic radiosurgery plus whole-brain radiation therapy vs stereotactic radiosurgery alone for treatment of brain metastases . JAMA . 2006 ; 295 ( 21 ): 2483 - 2491 . Google Scholar CrossRef Search ADS PubMed 16. Patchell RA , Tibbs PA , Walsh JW et al. A randomized trial of surgery in the treatment of single metastases to the brain . N Engl J Med . 1990 ; 322 ( 8 ): 494 - 500 . Google Scholar CrossRef Search ADS PubMed 17. Vecht CJ , Haaxma-Reiche H , Noordijk EM et al. Treatment of single brain metastasis: radiotherapy alone or combined with neurosurgery Ann Neurol. 1993 ; 33 ( 6 ): 583 - 590 . Google Scholar CrossRef Search ADS PubMed 18. Kalkanis SN , Kondziolka D , Gaspar LE et al. The role of surgical resection in the management of newly diagnosed brain metastases: a systematic review and evidence-based clinical practice guideline . J Neurooncol . 2010 ; 96 ( 1 ): 33 - 43 . Google Scholar CrossRef Search ADS PubMed 19. Carpentier A , McNichols RJ , Stafford RJ et al. Real-time magnetic resonance-guided laser thermal therapy for focal metastatic brain tumors . Neurosurgery . 2008 ; 63 ( 1 Suppl 1 ): ONS21 - ONS28 ; discussion ONS28-ONS29 . Google Scholar PubMed 20. von Elm E , Altman DG , Egger M et al. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement . Epidemiology . 2007 ; 18 ( 6 ): 800 - 804 . Google Scholar CrossRef Search ADS PubMed 21. McLaughlin N , Ditzel Filho LF , Prevedello DM , Kelly DF , Carrau RL , Kassam AB . Side-cutting aspiration device for endoscopic and microscopic tumor removal . J Neurol Surg B . 2012 ; 73 ( 01 ): 11 - 20 . Google Scholar CrossRef Search ADS 22. Paek SH , Audu PB , Sperling MR , Cho J , Andrews DW . Reevaluation of surgery for the treatment of brain metastases: review of 208 patients with single or multiple brain metastases treated at one institution with modern neurosurgical techniques . Neurosurgery . 2005 ; 56 ( 5 ): 1021 - 1034 ; discussion 1021-1034 . Google Scholar PubMed 23. Gaspar LE , Mehta MP , Patchell RA et al. The role of whole brain radiation therapy in the management of newly diagnosed brain metastases: a systematic review and evidence-based clinical practice guideline . J Neurooncol . 2010 ; 96 ( 1 ): 17 - 32 . Google Scholar CrossRef Search ADS PubMed 24. Mehta MP , Paleologos NA , Mikkelsen T et al. The role of chemotherapy in the management of newly diagnosed brain metastases: a systematic review and evidence-based clinical practice guideline . J Neurooncol . 2010 ; 96 ( 1 ): 71 - 83 . Google Scholar CrossRef Search ADS PubMed 25. Linskey ME , Andrews DW , Asher AL et al. The role of stereotactic radiosurgery in the management of patients with newly diagnosed brain metastases: a systematic review and evidence-based clinical practice guideline . J Neurooncol . 2010 ; 96 ( 1 ): 45 - 68 . Google Scholar CrossRef Search ADS PubMed 26. Rahmathulla G , Recinos PF , Kamian K , Mohammadi AM , Ahluwalia MS , Barnett GH . MRI-guided laser interstitial thermal therapy in neuro-oncology: a review of its current clinical applications . Oncology . 2014 ; 87 ( 2 ): 67 - 82 . Google Scholar CrossRef Search ADS PubMed 27. Agboola O , Benoit B , Cross P et al. Prognostic factors derived from recursive partition analysis (RPA) of Radiation Therapy Oncology Group (RTOG) brain metastases trials applied to surgically resected and irradiated brain metastatic cases . Int J Radiat Oncol Biol Phy . 1998 ; 42 ( 1 ): 155 - 159 . Google Scholar CrossRef Search ADS 28. Tendulkar RD , Liu SW , Barnett GH et al. RPA classification has prognostic significance for surgically resected single brain metastasis . Int J Radiat Oncol Biol Phys . 2006 ; 66 ( 3 ): 810 - 817 . Google Scholar CrossRef Search ADS PubMed 29. Patel AJ , Suki D , Hatiboglu MA et al. Factors influencing the risk of local recurrence after resection of a single brain metastasis . J Neurosurg . 2010 ; 113 ( 2 ): 181 - 189 . Google Scholar CrossRef Search ADS PubMed 30. Patel AJ , Suki D , Hatiboglu MA , Rao VY , Fox BD , Sawaya R . Impact of surgical methodology on the complication rate and functional outcome of patients with a single brain metastasis . J Neurosurg . 2015 ; 122 ( 5 ): 1132 - 1143 . Google Scholar CrossRef Search ADS PubMed 31. Zada G , Yashar P , Robison A et al. A proposed grading system for standardizing tumor consistency of intracranial meningiomas . Neurosurg Focus . 2013 ; 35 ( 6 ): E1 . Google Scholar CrossRef Search ADS PubMed 32. Yin Z , Hughes JD , Glaser KJ et al. Slip interface imaging based on MR-elastography preoperatively predicts meningioma-brain adhesion . J Magn Reson Imaging . 2017 ; 46 ( 4 ): 1007 - 1016 . Google Scholar CrossRef Search ADS PubMed 33. Bander ED , Jones SH , Kovanlikaya I , Schwartz TH . Utility of tubular retractors to minimize surgical brain injury in the removal of deep intraparenchymal lesions: a quantitative analysis of FLAIR hyperintensity and apparent diffusion coefficient maps . J Neurosurg . 2016 ; 124 ( 4 ): 1053 - 1060 . Google Scholar CrossRef Search ADS PubMed Supplemental digital contentis available for this article at www.operative-neurosurgery-online.com. Supplemental Digital Content. Video. Illustrative case demonstrating resection of a metastatic lesion. Copyright © 2018 by the Congress of Neurological Surgeons http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Operative Neurosurgery Oxford University Press

Multicenter Investigation of Channel-Based Subcortical Trans-Sulcal Exoscopic Resection of Metastatic Brain Tumors: A Retrospective Case Series

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Oxford University Press
Copyright
Copyright © 2018 by the Congress of Neurological Surgeons
ISSN
2332-4252
eISSN
2332-4260
D.O.I.
10.1093/ons/opy079
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Abstract

Abstract BACKGROUND Recent advancements have aimed to optimize visualization and minimize insult to healthy cortical and subcortical tissue through the use of tubular-based retractors. OBJECTIVE To investigate outcomes following resection of cerebral metastases using an integrated tubular retraction system with an exoscope and neuronavigation. METHODS A multicenter retrospective analysis of surgical outcomes in consecutive patients who underwent resection of a brain metastasis using a tubular retraction system and exoscope was performed. RESULTS Twenty-five patients were included, with a mean age of 61 yr (24-81 yr). Primary sources included lung (n = 13), breast (n = 3), renal cell (n = 3), and other (n = 6). Locations were frontal (n = 5), parietal (n = 8), cerebellar (n = 8), occipital (n = 3), and splenium (n = 1). Most lesions had a maximum diameter > 3.0 cm (n = 20) and a tumor depth > 4 cm (n = 14). Conversion to open (microscopic) craniotomy was not required in any case. Gross total resection was achieved in 20 cases (80.0%) and subtotal resection in 5 cases (20.0%). Median hospital stay was 2 d (1-12 d). All patients underwent postoperative radiation therapy. Perioperative complications developed in 1 patient (4.0%; hemiparesis and subsequent deep vein thrombosis). At 3-mo follow-up, no mortalities were observed, 19 patients (76.0%) demonstrated neurological improvements, 5 patients (20.0%) had a stable neurological exam, and 1 patient (4.0%) had a neurological decline. CONCLUSION Utilization of a channel-based, navigable retractor and exoscope is a feasible option for surgical resection of metastatic brain lesions. Deep-seated lesions, Neuro-oncology, Minimally invasive surgery, Tubular retractor, Exoscope, Intraoperative navigation, Surgical technique Recent advancements in cranial neurosurgery aim to optimize visualization and minimize insult to healthy brain tissue through the use of tubular or channel-based retractors. To date, many neurosurgical techniques have been performed with the aid of the microscope, endoscope, and exoscope using tubular retraction systems.1-3 While the surgical microscope provides direct binocular and stereoscopic vision, limitations can include depth of field, illumination, and ergonomics when working in deep corridors. On the other hand, endoscopic visualization offers improved panoramic visualization and illumination, but must be inserted into the surgical cavity and may pose a challenge when working within a limited surgical corridor. To overcome aforementioned obstacles, the use of an exoscope has been proposed, given that it has a wider focal distance and volume of focus, while providing high-quality views of the surgical field on a monitor.1,4 Thus, there has been a growing interest in investigating the use of the exoscope with modern tubular retraction systems for accessing subcortical brain lesions.1,2,4-6 The first reports of tubular retraction systems were introduced over 30 yr ago for resection of deep brain lesions,7-9 but because of the requirement for stereotactic frames, limited visualization, and availability of adequate surgical instruments, the widespread adoption of the approach remained hindered.1,3,4 More recently, many shortcomings associated with prior tubular retractor systems were overcome with the integration of new channel designs and optical technology that allow bimanual surgery through a minimally invasive corridor while using a frameless navigation system. Tubular retractors with microscopes or endoscopes have previously been shown to provide safe access for the resection of deep-seated brain lesions.10,11 Visualization may be further enhanced with an exoscope, as they have been shown to be safe and effective in hematoma evacuation,5,6 brain tumors,12 and in the resection of intra- or periventricular lesions.2 The safety and feasibility in the resection of metastatic brain tumors with an exoscopic tubular retractor system remains unclear. Brain metastases are the most common central nervous system neoplasms, and their incidence continues to rise with improvements in diagnostic modalities and systemic treatments.13 Treatment options include radiosurgery or whole brain radiation therapy, laser-induced thermal therapy (LITT), or traditional open craniotomy for surgical resection.14-19 Prior class I studies have shown greater survival and functional independence with surgical resection of solitary brain metastasis followed by radiation therapy vs those treated with radiation therapy alone.16-18 However, no preferred treatment option exists for larger, subcortical deep-seated metastases with mass effect and surrounding edema. These lesions may not be ideal candidates for radiosurgery alone due to large tumor volumes with significant surrounding edema and long-term steroid dependence. Objectives The authors sought to determine the safety and feasibility in the use of an integrated tubular retractor with an exoscope for resecting carefully selected metastatic brain lesions. To this end, we retrospectively analyzed surgical outcomes from utilization of a tubular retraction system with an exoscope for the resection of metastatic brain tumors across 6 institutions. METHODS Study design and Setting This is a retrospective analysis across 6 centers in the USA from 2012 to 2017. The database contained all patients who underwent cranial surgery with the use of an integrated tubular retraction system (BrainPath, NICO Corporation, Indianapolis, Indiana) and exoscope. Written informed consent for surgical resection was obtained as per regular protocol. Institutional review board and ethics committee approval was obtained for retrospective analysis. This article adhered to the reporting guideline of Strengthening the Reporting of Observational studies in Epidemiology.20 Participants Indications for surgical resection included patients that were symptomatic from mass effect and for confirmation of the unknown diagnosis. Patients with pathology-proven metastatic brain tumors measuring ≥ 2 cm at the widest diameter with at least 3-mo follow-up data were included. All patients underwent an oncologic evaluation to evaluate their systemic tumor burden and general medical health. Only patients with solitary metastatic brain lesions were included in this study. Patients with previous metastatic brain tumor resections, poor Karnofsky Performance Status score (<70), uncontrolled systemic disease, and/or leptomeningeal disease were excluded from the analysis. Study Size and Bias Limited data were available for a power analysis due to the novelty of this investigation; therefore, the study design was limited to a pilot study. To limit bias, consecutive patients from multiple institutions were included. Variables and Data Sources/Measurement The demographics, clinical, and imaging data of all patients were collected and entered into a secured spreadsheet. Data on the metastatic lesions, including location, maximal diameter (2-3 cm or >3 cm), depth (<2 cm, 2-4 cm, or >4 cm), final pathologic diagnosis, and intraoperative tumor core and capsule characteristics (surgeon's perspective of soft vs firm) were collected. Data on maximal diameter and depth were stratified based on prior reports1,5,10,12 and hypothesized impact on surgical outcome with the use of the exoscopic-tubular retractor technique. Tumor resection was analyzed based on postoperative magnetic resonance imaging (MRI) and was defined as gross-total resection (GTR) or subtotal resection (STR). Additional outcomes including hospital stay, perioperative complications, immediate and 90-d neurological outcomes (either improved, stable, or worse) were collected. Mortality was classified as postoperative deaths within 30 d of surgery or otherwise as related to systemic disease (90-d mortality). Statistical Methods Statistical significance in potential associations with tumor characteristics, size, and depth on the extent of resection were analyzed with SPSS v24 (IBM, Armonk, New York). In select cases, missing data were obtained from the electronic medical record. No patients were lost to follow-up. Exoscopic Channel-Based Protocol Frameless stereotactic navigation was utilized to plan a surgical corridor. In select cases, diffusion tensor imaging was used to plan an approach around critical subcortical white matter tracts. The BrainPath (NICO Corporation) surgical port was used in all cases, and comprises an inner obturator and an outer sheath. The navigation probe was placed inside the obturator to guide the planned trajectory and cannulation via a trans-sulcal approach. Operative visualization was obtained with an exoscope (Karl Storz Endoscopy, Tuttlingen, Germany or Synaptive Medical, Toronto, Canada)1,4 which was secured to a pneumatic holder (Karl Storz Endoscopy) for mobilization. Operative Technique All cases were performed under general endotracheal anesthesia except for 2 cases, which were performed with anesthesia for awake craniotomies. A small craniotomy overlying the planned trans-sulcal trajectory was performed. A small (≥13 mm) durotomy and arachnoid opening was made, and the port was introduced under navigation guidance until the obturator tip reached the planned target (Video, Supplemental Digital Content). The inner obturator was then removed, and the outer sheath was secured to a standard surgical retractor. Tumor resection was performed using standard bimanual microsurgical methods, a side-cutting aspirator (Myriad from NICO Corporation), and/or ultrasonic aspirating instruments as needed.2,21 In general, hemostasis was successfully acquired through standard microsurgical techniques, with bayoneted bipolar forceps and the application of standard hemostatic agents. RESULTS Patient Characteristics Twenty-five patients (Table) with metastatic lesions were included in the analysis (12 male, 13 female). The mean age at surgical resection was 61 yr (range 24-81 yr). Primary cancer sources included lung (n = 13), breast (n = 3), liver (n = 2), prostate (n = 1), renal cell (n = 3), colon (n = 2), and salivary gland (n = 1). They were located in parietal (n = 8), cerebellar (n = 8), frontal (n = 5), occipital (n = 3), and splenium (n = 1) regions. Twenty lesions had a maximum diameter of >3.0 cm and 5 lesions were between 2.0 and 3.0 cm. Tumor depth was >4 cm in 14 patients, 2.0 and 4.0 cm in 5 patients, and <2 cm in 6 patients. TABLE. Summary of patient data included in this study Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 DVT, deep vein thrombosis; GTR, gross total resection; L, indicates left; Path, pathology; POD, postoperative day; R, indicates Right; STR, subtotal resection. View Large TABLE. Summary of patient data included in this study Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 Lesion (cm) Characteristics POD Surgical Nonsurgical Neurological No. Sex Age Path Location Size Depth Resection Core Capsule Discharge Complications Complications Outcomes 1 F 54 Breast L Occipital >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 2 F 55 Breast L Parietal >3.0 2.0-4.0 GTR Soft Soft 1 None None Improved—Day 90 3 F 50 Breast R Frontal >3.0 <2.0 GTR Firm Firm 2 None None Improved—Day 90 4 M 78 Colon L Parietal 2.0 -3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 5 F 58 Colon R Parietal >3.0 >4 STR Soft Firm 2 None None Improved—Day 90 6 F 40 Liver L Splenium 2.0 -3.0 >4 GTR Soft Firm 11 None None Stable—Day 90 7 M 62 Liver R Parietal 2.0 -3.0 >4 GTR Soft Firm 2 None None Stable—Day 90 8 M 63 Lung Cerebellar >3.0 <2.0 GTR Soft Soft 1 None None Improved—Day 90 9 M 65 Lung L Parietal >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 10 F 72 Lung L Occipital >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 11 M 54 Lung Cerebellar >3.0 2.0-4.0 GTR Soft Soft 2 None None Improved—Day 90 12 F 51 Lung Cerebellar >3.0 2.0-4.0 GTR Firm Firm 1 None None Improved—Day 90 13 F 24 Lung L Frontal >3.0 >4 STR Firm Firm 7 R hemiparesis DVT Worse—Day 90 14 M 66 Lung R Frontal >3.0 >4 GTR Soft Firm 12 None None Improved—Day 90 15 F 53 Lung L Occipital >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 16 M 49 Lung L Cerebellar >3.0 >4 STR Firm Firm 2 None None Stable—Day 90 17 F 63 Lung L Cerebellar >3.0 >4 GTR Firm Firm 5 None None Improved—Day 90 18 F 72 Lung R Frontal >3.0 >4 STR Firm Firm 10 None None Improved—Day 90 19 M 41 Lung L Parietal 2.0 -3.0 >4 GTR Firm Firm 2 None None Improved—Day 0 20 F 78 Lung R Cerebellar 2.0 -3.0 >4 GTR Firm Firm 6 None None Improved—Day 90 21 M 63 Prostate R Parietal >3.0 <2.0 GTR Soft Soft 6 None None Improved—Day 30 22 M 53 Renal R Frontal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 23 M 53 Renal R Parietal >3.0 <2.0 GTR Soft Soft 2 None None Improved—Day 90 24 F 69 Renal R Cerebellar >3.0 >4 GTR Firm Firm 3 None None Stable—Day 90 25 M 46 Salivary Cerebellar vermis >3.0 >4 STR Firm Firm 3 None None Improved—Day 90 DVT, deep vein thrombosis; GTR, gross total resection; L, indicates left; Path, pathology; POD, postoperative day; R, indicates Right; STR, subtotal resection. View Large Surgical Outcomes Intraoperative conversion to a larger or open craniotomy or the use of a microscope was not required in any case. A transsulcal transcortical approach was used in all cases. A posterior transsulcal transcortical approach was utilized in the case of the lesion involving the splenium. Thirteen of the metastatic lesions were found to have a firm core and capsule, 7 were found to have a soft core and capsule, and 5 were found to have a soft core with a firm capsule. GTR was achieved in 20 cases (80.0%) and STR in 5 cases (20.0%). All cases with residual tumor had a firm capsule. The median postoperative hospital stay was 2 d (average = 3.5, range = 1-12 d). Complications occurred in 1 patient (4.0%), which included postoperative hemiparesis and subsequent deep vein thrombosis. This patient (Table: case no. 13) had a 3.5-cm lesion (measured at widest diameter) with a firm capsule and core located in the deep left frontal lobe adjacent to the posterior internal capsule. During surgical resection of the medial portion of this lesion, reductions in right-sided motor-evoked potentials were noted and the resection was aborted. The patient had postoperative hemiparesis that gradually resolved. The patient underwent gamma knife stereotactic radiosurgery (Elekta AB, Stockholm, Sweden) for the residual tumor and remained alive without progression of the lesion at 31-mo follow-up. No patients were lost to follow-up. At 3-mo follow-up, 19 patients (76.0%) demonstrated improvements in their neurological exam, 5 patients (20.0%) had a stable neurological exam, and 1 patient (4.0%) demonstrated new neurological deficits. All patients received postoperative radiosurgery to the resection cavity, except 1 patient (Table: case no. 18) who received whole brain radiation therapy at an outside facility. No mortalities were observed at 3-mo follow-up evaluations. Illustrative Case A 78-yr-old man with a past medical history of stage IV colon adenocarcinoma (Table: case no. 4) presented with complaints of speech difficulty, right-sided apraxia, and visual deficits (Video, Supplemental Digital Content). MRI showed a heterogeneously enhancing 2 cm mass within the left parietal periventricular white matter with a significant amount of perilesional vasogenic edema (Figure 1). Given the patient's neurological symptoms and location of lesion, surgical resection followed by adjuvant radiation was recommended. Under navigational guidance (Figure 2), a 3-cm craniotomy was performed on the left parieto-occipital region and a dural opening was made. A sulcus was identified for the entry point with navigation and dissected open (Figures 3-4). A 50 mm BrainPath retractor (NICO Corp) was inserted into the dissected sulcus and cannulated to a depth of 45 mm using navigation guidance, and then secured. The obturator was then removed and the exoscope was used to visualize and resect the tumor and the distal end of the port (Figure 5). The tumor was removed using a combination of suction, piecemeal resection, and side-cutting aspirator (NICO Myriad) until an intraoperative GTR was achieved. There were no changes in somatosensory or motor-evoked potential monitoring. Following meticulous hemostasis, the BrainPath tube was gently withdrawn, and hemostasis was achieved along the tract using Surgicel (Figure 6). Immediate postoperative imaging confirmed GTR (Figure 7). The final pathology diagnosis was consistent with metastatic colon adenocarcinoma. There were no complications associated with the surgery, and the patient was discharged home on postoperative day 2. He subsequently received adjuvant radiosurgery to the resection cavity followed by chemotherapy. At 3-mo follow-up, the patient's presenting neurological symptoms had resolved. MRI at that time demonstrated no evidence of residual or recurrent tumor. FIGURE 1. View largeDownload slide Example of preoperative imaging of deep-seated metastatic lesion. (Left) Preoperative T1-weighted MRI and (center) T1-weighted postcontrast MRI demonstrated 2.6 × 2.5 cm lobular heterogeneous enhancing lesion within the left parietal periatrial white matter, consistent with a metastatic lesion. (Right) FLAIR MRI demonstrated moderate to large amount of adjacent vasogenic edema and foci of hemorrhage within the lesion (seen on other sequences). FIGURE 1. View largeDownload slide Example of preoperative imaging of deep-seated metastatic lesion. (Left) Preoperative T1-weighted MRI and (center) T1-weighted postcontrast MRI demonstrated 2.6 × 2.5 cm lobular heterogeneous enhancing lesion within the left parietal periatrial white matter, consistent with a metastatic lesion. (Right) FLAIR MRI demonstrated moderate to large amount of adjacent vasogenic edema and foci of hemorrhage within the lesion (seen on other sequences). FIGURE 2. View largeDownload slide Navigation-guided trajectory. Frameless stereotactic navigation was utilized to plan and execute a surgical corridor based on assessing sagittal, coronal, and axial images. FIGURE 2. View largeDownload slide Navigation-guided trajectory. Frameless stereotactic navigation was utilized to plan and execute a surgical corridor based on assessing sagittal, coronal, and axial images. FIGURE 3. View largeDownload slide Identifying the appropriate sulcus is for BrainPath (NICO Corp) retractor entry. FIGURE 3. View largeDownload slide Identifying the appropriate sulcus is for BrainPath (NICO Corp) retractor entry. FIGURE 4. View largeDownload slide Opening the sulcus to introduce the tubular retractor. FIGURE 4. View largeDownload slide Opening the sulcus to introduce the tubular retractor. FIGURE 5. View largeDownload slide Demonstrating the view of the metastatic lesion with the tubular retractor and exoscope. FIGURE 5. View largeDownload slide Demonstrating the view of the metastatic lesion with the tubular retractor and exoscope. FIGURE 6. View largeDownload slide Showing the sulcal entry point after the tubular retractor was withdrawn and hemostasis was achieved along the tract using Surgicel. FIGURE 6. View largeDownload slide Showing the sulcal entry point after the tubular retractor was withdrawn and hemostasis was achieved along the tract using Surgicel. FIGURE 7. View largeDownload slide Example of postoperative imaging of deep-seated metastatic lesion. (Left) Immediate postoperative T1-weighted MRI and T1-weighted postcontrast MRI (center) demonstrated GTR of left parietal mass and decreased (right) signal on FLAIR. FIGURE 7. View largeDownload slide Example of postoperative imaging of deep-seated metastatic lesion. (Left) Immediate postoperative T1-weighted MRI and T1-weighted postcontrast MRI (center) demonstrated GTR of left parietal mass and decreased (right) signal on FLAIR. DISCUSSION Brain metastases are the most common intracranial neoplasms, and their reported incidence continues to increase.13 When used in combination with radiation-based treatments, surgical resection has been advocated as a primary option for patients with brain metastasis.13,18,22 The current multi-institutional consecutive case series demonstrated that utilization of a navigable tubular retractor and exoscope appears to be safe and feasible surgical option for trans-sulcal resection of carefully selected metastatic brain lesions. The resection of single, symptomatic brain metastases in conjunction with radiation-based treatments has previously been shown to demonstrate an overall survival benefit in class I studies.16,17 Additional benefits with the current approach may include shorter hospital length of stay, safer tissue acquisition, while optimizing target volume for radiosurgery. Multiple treatment options are available and should be carefully considered for patients with brain metastases.18,23-25 Most patients with brain metastases can be treated with radiation-based treatments. Larger (>2.5 cm), symptomatic, isolated, and surgically accessible metastases should be given strong consideration for surgical resection.16,17 For larger tumors that are not ideal candidates for radiosurgery (larger tumor volumes, surrounding vasogenic edema, and/or long-term corticosteroid dependence), options can include surgical resection or LITT.18,26 Trans-sulcal channel-based approaches with adjuvant radiosurgery may also be a viable option. Acquiring GTR of brain metastases has been shown to improve patient survival in retrospective comparative studies.27,28 Resection of metastatic lesions through the port, even those prone to hemorrhage, did not present as a major obstacle for resection. While GTR was obtained in most cases, STRs occurred with deep-seated lesions located nearby eloquent regions. This obstacle was encountered when the metastatic lesion involved the corticospinal tract adjacent to the posterior internal capsule. Intraoperative motor-evoked potential signals declined, and the patient developed postoperative right-sided hemiparesis (Table: case no. 14). This case may have benefited from concurrent intraoperative subcortical motor mapping, but this was not feasible with the retractor system. Tumors were resected in a piecemeal fashion, as an en bloc resection was not feasible with this approach. Previous investigations have suggested that piecemeal resection of single metastatic brain lesions may increase the risk for leptomeningeal disease and local recurrence when compared to en bloc resection.29,30 However, postoperative radiotherapy was performed in all cases included in their investigation, and it is unclear if the benefit of en bloc resection would still be present with modern postoperative radiation treatment options. The current study is limited by a short follow-up, but none of the cases included in the current study had signs of leptomeningeal disease and almost all patients were followed up with postoperative stereotactic radiosurgery. When lesions are adjacent to eloquent motor or speech regions, resection through a piecemeal fashion of tumors nearby eloquent regions may be preferred in an effort to avoid postoperative deficits. In these cases, STR with the goal of optimizing an adaptive target for subsequent stereotactic radiosurgery may be the preferred option. On the other hand, the resection of metastatic tumors nearby eloquent regions through a piecemeal fashion has not been shown to be safer in retrospective comparative case studies.30 The tumor's consistency (ie, firmness) is an important factor to be aware of, as it may become a surgical obstacle. Although a statistical association with the consistency of the metastatic tumor was not observed due to a low-powered investigation, it was felt that a softer tumor consistency was more amenable for channel-based resection. This is in line with reports that the soft consistency of intracerebral hematomas likely facilitates channel-based evacuation.5,6 Predicting the consistency of tumors, including adhesion to surrounding brain parenchyma, could provide valuable information for preoperative planning and predicting the extent of resection.31,32 Unfortunately, the current study did not have a large enough sample size to evaluate for significant correlations with tumor consistency. New magnetic resonance elastography based techniques have been shown to predict the degree of meningioma to brain parenchyma adhesions,32 and the investigation into the integration of these techniques may prove useful. The size of the tumor has also previously been reported to be less important than the consistency and anatomical location.2,10 Eliyas et al2 retrospectively analyzed 20 patients that underwent surgical resection with a tubular retractor and exoscope for lesions with average depths of 4.37 cm from the cortex. The authors achieved GTR in 85% of cases, and observed STRs with lesions that invaded eloquent regions. GTR rates in our case series were similar to patients treated surgically for metastatic lesions with high functional scores.22 Although a direct comparison cannot be drawn, median postoperative hospital stay appeared to be lower than prior reports (2 vs 6-7 d).13,22 Hospital stay may also vary due to required additional diagnostic evaluations/consultations or length of inpatient rehabilitation. The use of tubular retractors with an exoscope has previously shown promising results with evacuation of intracerebral hemorrhages and tumors.2,5,6,12 Recently, Day12 reported their experience with using this technique, and observed GTR in 19 of 20 metastatic brain lesions, 1 mortality due to pulmonary complications in a patient with nonsmall cell lung carcinoma and 1 postoperative hemorrhage that did not require surgical evacuation. The majority of their complications occurred in patients with gliomas and details on neurological outcomes were not reported. Bander et al33 retrospectively analyzed postoperative magnetic resonance fluid-attenuated inversion-recovery (FLAIR) hyperintensity and diffusion-weighted imaging of 20 patients that underwent resection of a deep-seated brain lesion with a METRx tubular retractor system with a microscope or endoscope. The authors achieved GTR in 75%, near-total resection in 10%, and STR in 15% of patients. Traditional retractors were found to have more postoperative restricted diffusion, but the results were not significant. This may be due to low power or the lack of objective volumetric analysis. The use of an endoscope with modern tubular retractors has previously been shown to result in higher rates of STRs.10,11 Limitations This study is limited by its retrospective study design and additional information on adjuvant therapies and long-term outcomes (particularly on the incidence of leptomeningeal disease and local recurrence). The study is also confounded by selection bias for patients selected for this technique. The indication used for this technique was for large (>2 cm at the widest diameter) presumed metastatic lesions with peritumoral edema or mass effect making them suboptimal to manage with radiosurgery alone. The number of patients meeting these indications was low; therefore, further investigations are needed to help delineate which patients would benefit the most with tubular surgical resection of deep-seated lesions over open microsurgical surgery. Investigations on the functional status of patient, tumor burden, number of brain lesions, and its impact on predicting prognosis and survival is currently underway. Although this is a low-powered study with short follow-up, the feasibility and safety of this technique have both been highlighted during this time period. CONCLUSION In our initial multi-institutional experience, we demonstrated that the utilization of a navigable channel retractor and exoscope appears to be safe and feasible for surgical resection of subcortical metastatic brain lesions. Disclosures US Food and Drug Administration-approved access system (BrainPath, NICO Corporation, Indianapolis, Indiana). Dr Pradilla is Principal Investigator for the ENRICH trial (Early Minimally Invasive Removal of ICH), funded by NICO corporation. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Mamelak AN , Nobuto T , Berci G . Initial clinical experience with a high-definition exoscope system for microneurosurgery . Neurosurgery . 2010 ; 67 ( 2 ): 476 - 483 . Google Scholar CrossRef Search ADS PubMed 2. Eliyas JK , Glynn R , Kulwin CG et al. Minimally invasive transsulcal resection of intraventricular and periventricular lesions through a tubular retractor system: multicentric experience and results . World Neurosurg . 2016 ; 90 : 556 - 564 . Google Scholar CrossRef Search ADS PubMed 3. Greenfield JP , Cobb WS , Tsouris AJ , Schwartz TH . Stereotactic minimally invasive tubular retractor system for deep brain lesions . Neurosurgery . 2008 ; 63 ( 4 Suppl 2 ): 334 - 339 ; discussion 339-340 . 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Transsulcal parafascicular surgery using Brain Path® for subcortical lesions . Neurosurgery . 2017 ; 64 ( CN_suppl_1 ): 151 - 156 . Google Scholar CrossRef Search ADS PubMed 13. D’Andrea G , Palombi L , Minniti G , Pesce A , Marchetti P . Brain metastases: surgical treatment and overall survival . World Neurosurg . 2017 ; 97 : 169 - 177 . Google Scholar CrossRef Search ADS PubMed 14. Andrews DW , Scott CB , Sperduto PW et al. Whole brain radiation therapy with or without stereotactic radiosurgery boost for patients with one to three brain metastases: phase III results of the RTOG 9508 randomised trial . Lancet North Am Ed . 2004 ; 363 ( 9422 ): 1665 - 1672 . Google Scholar CrossRef Search ADS 15. Aoyama H , Shirato H , Tago M et al. Stereotactic radiosurgery plus whole-brain radiation therapy vs stereotactic radiosurgery alone for treatment of brain metastases . JAMA . 2006 ; 295 ( 21 ): 2483 - 2491 . Google Scholar CrossRef Search ADS PubMed 16. 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Utility of tubular retractors to minimize surgical brain injury in the removal of deep intraparenchymal lesions: a quantitative analysis of FLAIR hyperintensity and apparent diffusion coefficient maps . J Neurosurg . 2016 ; 124 ( 4 ): 1053 - 1060 . Google Scholar CrossRef Search ADS PubMed Supplemental digital contentis available for this article at www.operative-neurosurgery-online.com. Supplemental Digital Content. Video. Illustrative case demonstrating resection of a metastatic lesion. Copyright © 2018 by the Congress of Neurological Surgeons

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Operative NeurosurgeryOxford University Press

Published: Apr 18, 2018

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