T1 sagittal T1 axial T1 coronal

Diagnosis: Dandy-Walker complex

Dandy-Walker complex refers to the continuum between Dandy-Walker malformation and variant. In true Dandy-Walker malformation, there is enlargement of the posterior fossa secondary to cystic dilatation of the fourth ventricle as well as elevation of the torcula and variable hypoplasia of the cerebellum and vermis. The etiology is believed to be due to congenital atresia of the foramina of Luschka or Magendie. Other CNS anomalies are associated in 3/4 of patients with Dandy-Walker malformation including callosal agenesis in 1/4, holoprosencephaly, gray matter heterotopia in 1/4. Hydrocephalus is present in 80%. Other associations are hamartoma of the tuber cinereum, cleft palate, polydactyly and cardiac anomalies.

Dandy-Walker variant is characterized by less vermian hypoplasia, a normal size posterior fossa with less prominent cystic dilatation of the fourth ventricle. DWV has the same associations as DWM.

Other considerations in the differential diagnosis of posterior fossa cystic lesions are arachnoid cyst, mega cisterna magna, juvenile pilocytic astrocytoma, and hemangioblastoma. Arachnoid cysts of the posterior fossa tend to be in the midline or at the cerebellopontine angle. There may be hydrocephalus due to the mass effect of the cyst, but there is no vermian hypoplasia. The fourth ventricle is not enlarged but may be displaced. Mega cisterna magna will show continuation with the cisterna magna inferiorly. In MCM there is no hydrocephalus and the fourth ventricle and vermis are normal. Hemangioblastoma and juvenile pilocytic astrocytoma are intraaxial, cerebellar hemispheric lesions which typically demonstrate a contrast enhancing nodular component. In this case, the combination of enlarged posterior fossa with a cyst communicating with the fourth ventricle, vermian hypoplasia and callosal agenesis are most compatible with Dandy-Walker complex/malformation. Related Cases

Hemangioblastoma Cortical dysplasia Dandy-Walker complex