← Radiology signsAsk Alera

Molar tooth sign

NeuroMRI

The midbrain at the level of the isthmus shows thick, horizontally oriented superior cerebellar peduncles and a deep interpeduncular fossa, resembling a molar tooth.

What it means

The imaging hallmark of Joubert syndrome and related ciliopathies.

Mechanism

Vermian hypoplasia with failure of decussation and thickening of the superior cerebellar peduncles gives the midbrain its molar-tooth outline.

Associated conditions

  • Joubert syndrome
  • Joubert-related disorders (ciliopathies)
  • Cerebellar vermian hypoplasia
  • COACH and related syndromes

Pearls

  • It is best seen on axial images through the midbrain-pons junction.
  • Clinically it associates with the abnormal breathing and eye movements of Joubert syndrome.

References

  • Radiopaedia: Molar tooth sign

For educational use only. This dictionary is a study aid and reference, not a diagnostic tool, and must not be used to guide clinical decisions or patient care. Imaging appearances vary; always correlate with the full clinical picture and confirm with a qualified radiologist.