Abnormal midbrain morphology Molar tooth sign on MRI HP:0002419 Molar tooth sign on imaging An abnormal appearance of the midbrain in axial magnetic resonance imaging in which the elongated superior cerebellar peduncles give the midbrain an appearance reminiscent of a molar or wisdom tooth. UMLS:C1865060 Molar tooth sign Molar tooth sign on brain imaging 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. The absence of crossing fibers also leads to a reduction in the anteroposterior diameter of the midbrain and deepening of the interpeduncular cistern.