a condition characterized by an abnormal increase in the amount of fluid in the cranium, esp. in young children, causing enlargement of the head and deterioration of the brain
See hydrocephalus in American Heritage Dictionary 4
(hīˌdrō-sĕfˈə-ləs) also hy·dro·ceph·a·ly(-lē)
noun
A usually congenital condition in which an abnormal accumulation of fluid in the cerebral ventricles causes enlargement of the skull and compression of the brain, destroying much of the neural tissue.