Hydrocephalus, or "water on the brain," is the buildup of excess cerebrospinal fluid (CSF) within the brain. The pressure from the fluid buildup may lead to an injury to the brain if the condition is not treated.

Normally, CSF flows through and out of chambers in the brain called ventricles, and then around the brain and spinal cord, providing nutrition and a protective cushion. Hydrocephalus is caused by an imbalance between the brain's production of CSF and the body's ability to distribute or absorb it properly.

Hydrocephalus may be present at birth (congenital). It may also happen after a serious illness (such as meningitis) or a head injury.

Treatment usually includes draining the fluid spaces (ventricles) of the brain. This drainage may be done with a surgery to place a tube called a shunt in the brain.

Treatment can help prevent long-term problems.