Dandy-Walker malformation HP:0001305 human_phenotype HP:0001313 MSH:D003616 A congenital brain malformation typically characterized by incomplete formation of the cerebellar vermis, dilation of the fourth ventricle, and enlargement of the posterior fossa. In layman's terms, Dandy Walker malformation is a cyst in the cerebellum (typically symmetrical) that is involved with the fourth ventricle. This may interfere with the ability to drain cerebrospinal fluid from the brain, resulting in hydrocephalus. Dandy Walker cysts are formed during early embryonic development, while the brain forms. The cyst in the cerebellum typically has several blood vessels running through it connecting to the brain, thereby prohibiting surgical removal. Dandy-Walker cyst Dandy-walker anomaly HP:0006809 UMLS:C0010964 SNOMEDCT_US:14447001 Cerebellar vermis hypoplasia Dilated fourth ventricle Cerebellar cyst Enlarged posterior fossa