Applied Radiology

Diagnosis

Joubert Syndrome

Findings

Two axial T2-weighted images and a coronal T1-weighted image (T1-WI) are provided. The first axial image demonstrates enlargement of the superior cerebellar peduncles, resulting in a classic “molar tooth” appearance. The second axial image demonstrates severe hypoplasia of the cerebellar vermis with resultant enlargement of the fourth ventricle. The fourth ventricle does not have a classic “bat wing” appearance, which has been described with Joubert Syndrome. The coronal T1-WI also demonstrates enlarged, elongated superior cerebellar peduncles and severe cerebellar hypoplasia.

Discussion

Joubert Syndrome is an autosomal recessive disorder, which may present clinically with some combination of the following symptoms: Ataxia, global developmental delay, hypotonia, abnormal ocular movements, facial dysmorphism, and episodic hyperpnea. The syndrome is also associated with multicystic dysplastic kidneys, polydactyly, ocular abnormalities, such as colobomas and retinal dysplasias, and hepatic fibrosis.

Joubert Syndrome demonstrates a characteristic radiographic appearance, which is most often diagnosed with MRI. The characteristic imaging finding is aplasia or dysplasia of the cerebellar vermis with enlarged, elongated superior cerebellar peduncles. On axial images, this combination of findings results in a “molar tooth” appearance. Additionally, absence of the pyramidal decussation results in a triangular-shaped fourth ventricle, which has been termed a “bat wing” fourth ventricle. Supratentorial abnormalities in patients with Joubert Syndrome are rare, so findings such as ventriculomegaly should prompt consideration of other diagnoses.

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