Dilation of the fourth ventricle resulting in hypoplasia of the midline portion of the cerebellum and enlargement of the posterior fossa.
Often secondary to atresia of the foramina of Luschka and Magendie.
Usually presents with a cystic deformity of the fourth ventricle, hypoplasia of the cerebellar vermis, and an enlarged posterior fossa: a genetically heritable disease. (0.003%/births).
Patients often present with developmental problems, enlarged head circumference and signs and symptoms of hydrocephalus.
Cerebeller involvement may result in impaired balance, plasticity ad poor fine motor control.
Associated with fourth ventricle cystic dilation.
Causes occipital bone to bulge posteriorly and displaces the tentorium upward.
Causes hypoplasia of the cerebellar vermis, and a deficient or absent corpus callosum.
MRI and CT scan of the brain identify an enlarged posterior fossa with a midline cyst.
Treatment is to shunt the hydrocephalus and prevent brain herniation.
70-90% of patients with this process develop neurological abnormalities without treatment.