Summary: A 28-year-old male with a lifelong learning disability is
referred to neurology for abnormal eye movements. He has had no previous
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.
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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