Molar tooth sign (CNS)

Last revised by Ammar Ashraf on 14 Mar 2023

The molar tooth sign refers to the appearance of the midbrain in an axial section in which the elongated superior cerebellar peduncles give the midbrain an appearance reminiscent of a molar or wisdom tooth.

It was initially described in Joubert syndrome and related disorders (JSRD) 2 but is now recognized to occur in a number of other conditions, e.g. nephronophthisis, hepatic fibrosis, Cogan's syndrome, and pontine tegmental cap dysplasia 4.

Molar tooth appearance results from a lack of normal decussation of superior cerebellar peduncular fiber tracts which in turn leads to enlargement of the peduncles, which also follow a more horizontal course 3.

The absence of crossing fibers also leads to a reduction in the anteroposterior diameter of the midbrain and deepening of the interpeduncular cistern 3.

See also

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