Molar tooth sign
 Discussion of Molar tooth sign
- The molar tooth sign is seen on transverse computed tomographic and magnetic resonance images obtained at the level of the midbrain in patients with Joubert syndrome.
- The term molar tooth refers to the characteristic appearance of an enlarged and horizontally directed tubular structure on each side of the midline emerging from the midbrain.
- The sign is caused by a lack of normal decussation of superior cerebellar peduncular fiber tracts.
- A lack of decussation leads to enlargement of the peduncles; in addition, the peduncles follow a more horizontal course as they extend perpendicularly to the brainstem between the midbrain and the cerebellum.
- The absence of crossing fibers is responsible for the decreased anteroposterior diameter of the midbrain and also causes the interpeduncular cistern to be deeper than that in the normal brain.
- The combination of these findings leads to the characteristic "molar tooth" appearance on transverse CT and MR images of the midbrain in patients with Joubert syndrome.
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 References for Molar tooth sign
- Peter McGraw. The Molar Tooth Sign. Radiology 2003 229: 671-672.