is a congenital brain malformation involving the cerebellum (an area at the back of the brain that controls movement) and the fluid-filled spaces around it. This condition is characterized by an enlargement of the fourth ventricle (a small channel that allows fluid to flow freely between the upper and lower areas of the brain and spinal cord), a partial or complete absence of the cerebellar vermis (the area between the two cerebellar hemispheres), and cyst formation near the internal base of the skull. This condition may present with an increase in fluid and pressure around the skull (hydrocephalus). It may also be associated with developmental delay, or malformations of the heart, face, limbs, fingers, or toes. The term "Dandy-Walker complex" represents a spectrum of abnormalities that includes Dandy-Walker variant, Dandy-Walker malformation, and mega cisterna magna. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.