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.
Kumar J, Kumar A, Saha S. The Molar Tooth Sign of Joubert Syndrome. Arch Neurol. 2007;64(4):602-603. doi:10.1001/archneur.64.4.602