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The Molar Tooth Sign of Joubert Syndrome

The Molar Tooth Sign of Joubert Syndrome A 1-year-old child presented with global developmental delay. Physical examination findings revealed hypotonia and abnormal eye movements. Magnetic resonance (MR) imaging of the brain (Figure 1 and Figure 2) revealed hypoplastic vermis with a narrow cleft separating the cerebellar hemispheres. The superior cerebellar peduncles were thickened and abnormally oriented perpendicular to the dorsum of the brainstem, giving the characteristic “molar tooth” sign. There was deepening of the interpeduncular fossa. The fourth ventricle was enlarged with a bat-wing appearance of the rostral fourth ventricle. The cerebellar hemispheres were normal and there was no assosciated supratentorial abnormality. These imaging findings were typical of Joubert syndrome. Figure 1 View LargeDownload T1-weighted axial magnetic resonance image through the pontomesencephalic junction shows a deep cleft in the isthmus of the brainstem, thickened and reoriented superior cerebellar peduncles, and vermian hypoplasia, which combine to give the “molar tooth” appearance. Figure 2 View LargeDownload T1-weighted axial magnetic resonance image through the rostral fourth ventricle shows the enlarged fourth ventricle with a bat-wing appearance. A midline cleft is noted reflecting vermian hypoplasia. Comment Joubert syndrome is a rare autosomal recessive disorder associated with cerebellar vermian hypoplasia. The vermian hypoplasia ranges from hypoplasia of the inferior vermis to agenesis of the entire vermis.1 Maria et al2 reviewed the clinical features of Joubert syndrome and provided revised diagnostic criteria. These include hypotonia, ataxia, global developmental delay, characteristic MR imaging, and pathological findings. The MR imaging shows molar tooth sign in the axial plane which consists of an abnormally deep cleft in the isthmus of the brainstem, thickened and reoriented superior cerebellar peduncles, and vermian hypoplasia. The pathological findings include vermian hypoplasia or dysplasia, elongation of the caudal midbrain tegmentum, and marked dyplasia of the caudal medulla. The associated abnormalities that may be seen include abnormal facies, episodic hyperpnea or apnea, ocular and oculomotor abnormalities, renal involvement, and other uncommon findings. Although vermian dysgenesis is the cardinal morphological feature, there may also be other morphological abnormalities of the cerebrum, cerebellum (excluding the vermis), or brainstem. When associated with additional abnormalities, the condition is named Joubert syndrome plus.3 Genetically, Joubert syndrome is a heterogeneous group of disorders with mapping to more than 1 chromosome site (9q34, 11p12-q13, 2q13, and 6q23). Two specific gene mutations have also been proposed: the AHI1 gene on chromosome 6q23, and the NPHP1 gene on chromosome 2q13.4 Better understanding of the clinical and radiological characteristics is paramount to successful genetic studies. Back to top Article Information Correspondence: Dr A. Kumar, 175, Minakshi Garden, P.O. Tilak Nagar, New Delhi-110018, INDIA (atinkumar@rediffmail.com). Author Contributions:Study concept and design: J. Kumar, Acquisition of data: J. Kumar A. Kumar, and Saha. Analysis and interpretation of data: J. Kumar and A. Kumar. Drafting of the manuscript: J. Kumar, A. Kumar, and Saha. Critical revision of the manuscript for important intellectual content: J. Kumar and A. Kumar. Administrative, technical, and material support: J. Kumar, A. Kumar, and Saha. Study supervision: J. Kumar and A. Kumar. Financial Disclosure: None reported. References 1. DeSouza NChoudhri RBingham JCox T MRI in cerebellar hypoplasia. Neuroradiology 1994;36148- 151PubMedGoogle ScholarCrossref 2. Maria BLBoltshauser EPalmer SCTran TX Clinical features and revised diagnostic criteria in Joubert syndrome. J Child Neurol 1999;14583- 590PubMedGoogle ScholarCrossref 3. Maria BLQuisling RGRosainz LC Molar tooth sign in Joubert syndrome: clinical, radiologic and pathologic significance. J Child Neurol199914368376PubMedGoogle Scholar 4. Online Mendelian Inheritance in Man. OMIM™ Johns Hopkins University, Baltimore, Md. MIM Number: %213300.http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=213300. Accessed March 30, 2006Google Scholar http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Neurology American Medical Association

The Molar Tooth Sign of Joubert Syndrome

Kumar, Jyoti; Kumar, Atin; Saha, Sanchita
Archives of Neurology , Volume 64 (4) – Apr 1, 2007
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References (4)

Publisher
American Medical Association
Copyright
Copyright © 2007 American Medical Association. All Rights Reserved.
ISSN
0003-9942
DOI
10.1001/archneur.64.4.602
pmid
17420326
Publisher site
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Abstract

A 1-year-old child presented with global developmental delay. Physical examination findings revealed hypotonia and abnormal eye movements. Magnetic resonance (MR) imaging of the brain (Figure 1 and Figure 2) revealed hypoplastic vermis with a narrow cleft separating the cerebellar hemispheres. The superior cerebellar peduncles were thickened and abnormally oriented perpendicular to the dorsum of the brainstem, giving the characteristic “molar tooth” sign. There was deepening of the interpeduncular fossa. The fourth ventricle was enlarged with a bat-wing appearance of the rostral fourth ventricle. The cerebellar hemispheres were normal and there was no assosciated supratentorial abnormality. These imaging findings were typical of Joubert syndrome. Figure 1 View LargeDownload T1-weighted axial magnetic resonance image through the pontomesencephalic junction shows a deep cleft in the isthmus of the brainstem, thickened and reoriented superior cerebellar peduncles, and vermian hypoplasia, which combine to give the “molar tooth” appearance. Figure 2 View LargeDownload T1-weighted axial magnetic resonance image through the rostral fourth ventricle shows the enlarged fourth ventricle with a bat-wing appearance. A midline cleft is noted reflecting vermian hypoplasia. Comment Joubert syndrome is a rare autosomal recessive disorder associated with cerebellar vermian hypoplasia. The vermian hypoplasia ranges from hypoplasia of the inferior vermis to agenesis of the entire vermis.1 Maria et al2 reviewed the clinical features of Joubert syndrome and provided revised diagnostic criteria. These include hypotonia, ataxia, global developmental delay, characteristic MR imaging, and pathological findings. The MR imaging shows molar tooth sign in the axial plane which consists of an abnormally deep cleft in the isthmus of the brainstem, thickened and reoriented superior cerebellar peduncles, and vermian hypoplasia. The pathological findings include vermian hypoplasia or dysplasia, elongation of the caudal midbrain tegmentum, and marked dyplasia of the caudal medulla. The associated abnormalities that may be seen include abnormal facies, episodic hyperpnea or apnea, ocular and oculomotor abnormalities, renal involvement, and other uncommon findings. Although vermian dysgenesis is the cardinal morphological feature, there may also be other morphological abnormalities of the cerebrum, cerebellum (excluding the vermis), or brainstem. When associated with additional abnormalities, the condition is named Joubert syndrome plus.3 Genetically, Joubert syndrome is a heterogeneous group of disorders with mapping to more than 1 chromosome site (9q34, 11p12-q13, 2q13, and 6q23). Two specific gene mutations have also been proposed: the AHI1 gene on chromosome 6q23, and the NPHP1 gene on chromosome 2q13.4 Better understanding of the clinical and radiological characteristics is paramount to successful genetic studies. Back to top Article Information Correspondence: Dr A. Kumar, 175, Minakshi Garden, P.O. Tilak Nagar, New Delhi-110018, INDIA (atinkumar@rediffmail.com). Author Contributions:Study concept and design: J. Kumar, Acquisition of data: J. Kumar A. Kumar, and Saha. Analysis and interpretation of data: J. Kumar and A. Kumar. Drafting of the manuscript: J. Kumar, A. Kumar, and Saha. Critical revision of the manuscript for important intellectual content: J. Kumar and A. Kumar. Administrative, technical, and material support: J. Kumar, A. Kumar, and Saha. Study supervision: J. Kumar and A. Kumar. Financial Disclosure: None reported. References 1. DeSouza NChoudhri RBingham JCox T MRI in cerebellar hypoplasia. Neuroradiology 1994;36148- 151PubMedGoogle ScholarCrossref 2. Maria BLBoltshauser EPalmer SCTran TX Clinical features and revised diagnostic criteria in Joubert syndrome. J Child Neurol 1999;14583- 590PubMedGoogle ScholarCrossref 3. Maria BLQuisling RGRosainz LC Molar tooth sign in Joubert syndrome: clinical, radiologic and pathologic significance. J Child Neurol199914368376PubMedGoogle Scholar 4. Online Mendelian Inheritance in Man. OMIM™ Johns Hopkins University, Baltimore, Md. MIM Number: %213300.http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=213300. Accessed March 30, 2006Google Scholar

Journal

Archives of Neurology – American Medical Association

Published: Apr 1, 2007

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