The molar tooth sign was initially identified in Joubert syndrome, named after Marie Joubert who first described it in 1968 as a rare autosomal recessive disorder characterised by the neuroradiological hallmark of the molar tooth sign caused by cerebellar vermian hypoplasia. Subsequently, it emerged that the molar tooth sign encompasses many syndromes that are now grouped together and termed Joubert syndrome and related disorders (JSRDs). Knowledge of the newer classification system and the subtypes is important and helps to direct and interpret imaging studies based on clinical signs so as to avoid delay in diagnosis of the hepatic oculorenal and renal subtypes of JSRDs in patients in whom the molar tooth sign is identified on brain MRI.

Joubert syndrome; molar tooth sign