joubert syndrome

Joubert reported five children with episodic hyperpnoea, abnormal eye movements, ataxia, and mental retardation in 1969. Joubert syndrome is a relatively rare developmental malformation with autosomal recessive transmission.It is characterized by the aplasia or hypoplasia of cerebellar vermis, but fragmentation and heterotopia of dentate nuclei, inferior olivary nuclei, and basis pontis are associated neuropathological findings. The nuclei and tracts of trigeminal nerve, solitary nuclei and tracts, and nuclei gracilis and cuneatus are also hypoplastic or fragmented in Joubert syndrome. The pyramidal decussation is almost totally absent.

The clinical presentation of Joubert syndrome is usually at a very early age. Clinical findings may include nonspecific features such as hypotonia, ataxia, with mental and motor retardation. Neuro-ophthalmologic examination of the patient reveals the presence of abnormal eye movements, characterized by partial to complete oculomotor apraxia, both in horizontal and vertical directions. Most patients have a medical history of respiratory disturbances, characteristically episodic attacks of hyperpnoea intermixed with central apnoea especially during the neonatal period.

Neuroimaging findings of Joubert syndrome are quite characteristic. Imaging features are isthmic dysgenesis, which is characterized by elongation and thinning of the pontomesencephalic junction, the so called isthmus, leading to deepening of the anterior interpeduncular fossa, together with thickening and elongation of the superior cerebellar peduncles. The most consistent radiological change of the syndrome is agenesis or hypogenesis of the vermis with a cleft formation. A portion of the superior vermis may be present in some cases with incomplete fusion of the halves of vermis, creating a sagittal vermian cleft. Sagittal images show a complete or nearly complete lack of the normal vermian folia. Absence of the vermis results in a triangular-shaped mid-fourth ventricle and a bat-wing-shaped fourth ventricle superiorly. Imaging in the axial plane demonstrates the molar tooth sign due to a deep posterior interpeduncular fossa, thick and elongated superior cerebellar peduncles, and hypoplastic or aplastic superior cerebellar vermis. The cerebellar hemispheres appose one another in the midline, but are not fused .Associated supratentorial anomalies are uncommon, however cerebral cortical dysplasia, grey matter heterotopia, occipital meningoencephalocele, callosal dysgenesis are rarely detected findings. Chorioretinal coloboma, retinal dystrophy, facial dysmorphism, sacral dermal sinus, polydactyly, scoliosis, congenital heart defects, congenital hepatic fibrosis, and polycystic kidney disease have been reported as rare extracranial findings in patients with Joubert syndrome.The prognosis is generally poor .