hydrocephalus, also known as water on the brain, developmental (congenital) or acquired condition in which there is an abnormal accumulation of body fluids within the skull. The congenital form may be associated with other abnormalities. The acquired form may follow meningitis or another cerebral inflammation or tumor. The accumulation of fluid causes compression of the brain and enlargement of the skull, sometimes with separation of bone structures. Paralysis and death may result or, at the least, mental retardation. Many forms of therapy, including surgery, have been attempted, but usually without much success in extreme cases.

Accumulation of cerebrospinal fluid (CSF) in the ventricles (cavities) of the brain. Hydrocephalus is caused by overproduction of CSF, congenital blockage that prevents drainage (see neural tube defect), or complications of head injuries or infections. Normally, CSF circulates through the brain and spinal cord and drains into the circulation. In infants and young children, hydrocephalus causes the brain and skull to enlarge because the fontanels have not yet closed. Without surgery to divert the excess fluid into the blood or abdomen, accumulating fluid eventually compresses the brain, causing convulsions, intellectual disability, and death.

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