hydroceph'alus

[G. hydor, water, kephale, head.] A condition, usually congenital, marked by an extensive effusion of serum into the cerebral ventricles, dilating these cavities, thinning the brain, and causing a separation of the cranial bones; there may also be an accumulation of fluid in the subarachnoid space, acute' h., basilar (tuberculous) meningitis, chron'ic h., a gradual accumulation of fluid in the ventricles of the brain, occurring in infancy, causing enlargement of the head and signs of mental deficiency. exter'nal h., an accumulation of fluid in the subarachnoid spaces of the brain, inter'nal h., h. in which the accumulation of fluid is confined to the ventricles, Whytt's disease.hydranencephaly. pri'mary h., chronic h. sec'ondary h., an accumulation of fluid in the cranial cavity, due to meningitis or obstruction to the venous flow.