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

This article examines the magnetic resonance imaging features that typify t he Joubert malformation. Specific morphologic features include: (1) dysgene sis of the isthmic portion of the brain stem at the pontomesencephalic junc tion, (2) abnormally thick superior cerebellar peduncles perpendicular to t he brain stem, (3) hypoplasia of the cerebellar vermis with consequent enla rgement of the 4th ventricle and rostral shift of the fastigium, and (4) sa gittal vermic clefting. At least two of these features were present in ever y patient and all were present in some. The only cerebral anomaly identifie d was mild prominence of the ventricles and subarachnoid spaces. The "Joube rt-plus anomaly" has been defined as the Joubert malformation plus addition al anomalies of either the mesencephalon or the caudal 4th ventricle; this likely represents a similar but more extensive embryologic defect. By placi ng a relative numeric value on each morphologic feature, a classification s cheme has been created that can quantitate the extent of the Joubert malfor mation in any individual case.