Term describing a condition in which fluid collects inside the skull.

Hydrocephalus, which means literally "water on the brain," is a condition in which excessive cerebrospinal fluid (CSF) collects inside the skull. This fluid is normally found in the brain, although excessive amounts of CSF may build pressure to levels that cause brain damage and subsequent disability.

The brain rests within the natural bony vault of the cranium. There it is protected by the skull and by layers of fibrous material that help to stabilize it and to contain the fluid that surrounds it. The brain itself is a very soft, gelatinous material that requires substantial protection. Three layers of connective tissue line the skull and surround the brain. The pia mater (which means literally "tender mother") lies directly on the brain, following its contours and continuing along the spinal cord as it descends through the spine. The...