Dandy-Walker syndrome: a congenital brain malformation (birth defect) involving the cerebellum (the area in the back of the brain that coordinates movement) and the fluid-filled spaces around it. It may be associated with other abnormalities in the central nervous system. Affected infants may have slow motor development and progressive enlargement of the skull. Older children may have symptoms such as irritability, unsteadiness, poor muscle coordination, jerky eye movements, or vomiting. Other possible symptoms can include enlarged head circumference, bulging at the back of the skull, breathing problems, and problems with the nerves that control the eyes, face and neck. Some affected people have normal intellectual function, while others may have cognitive impairment. Treatment is directed at managing symptoms; sometimes surgery is required to drain excess fluid buildup.