Hydrocephalus is a condition in which the primary characteristic is excessive accumulation of fluid in the brain. Although hydrocephalus was once known as "water on the brain," the "water" is actually cerebrospinal fluid (CSF) -- a clear fluid surrounding the brain and spinal cord. The excessive accumulation of CSF results in an abnormal dilation of the spaces in the brain called ventricles. This dilation causes potentially harmful pressure on the tissues of the brain.
Hydrocephalus is the buildup of too much cerebrospinal fluid in the brain. Normally, this fluid cushions the brain. When there is too much, though, it puts harmful pressure on the brain that tends to become enlarged, sometimes with little or no increase in intracranial pressure (ICP).