Molar tooth sign (CNS)

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 recognised to occur in a number of other conditions, e.g. nephronophthisis, hepatic fibrosis and in Cogan's syndrome.

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.

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Article information

rID: 8241
Section: Signs
Synonyms or Alternate Spellings:
  • CNS molar tooth sign

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