The MRI of the brain establishes the diagnosis of Joubert syndrome. The superior cerebellar peduncles are prominent and have horizontal courses. These characteristics of the superior peduncles, in association with a deep interpeduncular fossa, produce the molar tooth sign on axial view. Sagittal images of the fourth ventricles reveal the batwing sign due to the convex appearance of the upper fourth ventricular wall. Hydrocephalus may also occur but is rare. Cervicomedullary abnormalities are often present. Patients with Joubert syndrome may have retinal dystrophy and cystic kidneys. Joubert syndrome must be differentiated from romboencephaloclasis.

Romboencephaloclasis
Romboencephaloclasis is characterized by absence or hypoplasia of the cerebellar vermis and fusion of the cerebellar hemispheres. Rhomboencephaloclasis is associated with other central nervous system malformations. The most frequent associated anomalies are fusion of the cerebellar dentate nuclei, superior cerebellar peduncles, and thalami. Magnetic resonance imaging is diagnostic.