Magnetic resonance imaging features and classification of central nervous system malformations in Joubert syndrome.

This article examines the magnetic resonance imaging features that typify the Joubert malformation. Specific morphologic features include: (1) dysgenesis of the isthmic portion of the brain stem at the pontomesencephalic junction, (2) abnormally thick superior cerebellar peduncles perpendicular to the brain stem, (3) hypoplasia of the cerebellar vermis with consequent enlargement of the 4th ventricle and rostral shift of the fastigium, and (4) sagittal vermic clefting. At least two of these features were present in every patient and all were present in some. The only cerebral anomaly identified was mild prominence of the ventricles and subarachnoid spaces. The "Joubert-plus anomaly" has been defined as the Joubert malformation plus additional anomalies of either the mesencephalon or the caudal 4th ventricle; this likely represents a similar but more extensive embryologic defect. By placing a relative numeric value on each morphologic feature, a classification scheme has been created that can quantitate the extent of the Joubert malformation in any individual case.