Molar tooth sign on MRI is associated with which condition?

• A. SCA
• B. Joubert's Syndrome
• C. Friedrich's Ataxia
• D. Ataxia Telangiectasia

Answer: (B)

The imaging hallmark here is the molar tooth sign, which points to Joubert syndrome. This sign arises when the superior cerebellar peduncles are abnormally thick and oriented horizontally, with a deepened interpeduncular fossa, creating a silhouette that resembles a molar tooth on axial MRI views. Joubert syndrome is a ciliopathy characterized by hypoplasia of the cerebellar vermis and brainstem malformations, and clinically it presents in infancy with hypotonia, ataxia, and irregular breathing or ocular movement abnormalities—findings that fit the context of this MRI feature. Other conditions listed can cause ataxia or cerebellar involvement but do not produce the distinctive molar tooth appearance, so they are not the best match for this imaging sign.