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At a glance

It is classified as a rare congenital human brain anomaly of the cerebellum and fourth ventricle. It is characterized by hypoplasia of the cerebellum, absence of the cerebellar vermis, and consequently noncommunicating hydrocephalus that is caused by cystic expansion of the fourth ventricle in the posterior fossa. The clinical features include abnormal motor coordination, raised intracranial pressure due to accumulation of the cerebrospinal fluid, and other multiple brain function problems. It is typically a lifelong disorder. Other systemic malformations are reported between 47 and 81% of DWS patients and include urogenital, renal, cardiac, intestinal, and craniofacial defects.


Dandy-Walker Cyst; Luschka-Magendie Foramina Atresia; Hydrocephalus Noncommunicating Dandy-Walker Type; Dandy-Walker Deformity; Hydrocephalus Internal Dandy-Walker Type.


There are four subtypes that have been described in which multiple organs are affected to varying degrees; however, the fundamental abnormalities involve the cerebellum and muscle coordination. The four conditions consist of:

  • DWS Malformation: Most severe condition where the posterior fossa is largely cystic, filling up the entire fossa, compressing the cerebellar, pushing upward the cerebellar tissue throughout the tentorium, causing compression of the seventh cranial nerves on the edges of the falx cerebri. There is a complete agenesis of the vermis. This is most often associated with a spina bifida and noncommunicating hydrocephalus. The rise in intracranial pressure is consequent to the enlarged posterior fossa and the bulge of the tentorium into the upper cranial cavities.

  • DWS Mega Cisterna Magna: Variation of the posterior fossa anatomy that causes enlarged retrocerebellar cisterns with otherwise normal cerebellar morphology. The cerebellar hemispheres and vermis are normal, but the cisterna magna is significantly enlarged, measuring greater than 10 mm on oblique transverse radiological plane. When the disorder is isolated, the prognosis is favorable. However, one-third of children with central nervous system anomalies associated with a mega cisterna magna usually present cognitive, motor and language delay as well as cerebellar ataxia.

  • DWS Variant: Characterized by a less severe clinical presentation and neurological malformation. The fourth ventricle is mildly enlarged and the external compression onto the cerebellar tissue is less significant as observed in the other two subtypes. The cerebellar vermis is hypoplastic and is accompanied with variable sized cyst. In this case, the fourth ventricle communicates with the cisterna magna through an enlarged vallecula. Hydrocephalus is present in 25% of cases and supratentorial central nervous system manifestations are only present in 20% of affected individuals. The third and lateral ventricles as well as the brain stem are normal.

  • Blake’s Pouch Cyst: Posterior ballooning of the superior medullary velum into the cisterna magna. Patients present with delayed neurological development, with normal outcomes at 1 to 5 years old.


The true incidence remains unknown as it is a disorder that occurs sporadically in approximately 1:25,000 to 30,000 live births worldwide. It accounts for ...

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