May also be called: Water on the Brain

Hydrocephalus (sometimes called "water on the brain") is a brain condition that happens when cerebrospinal fluid — the clear, watery fluid that surrounds and cushions the brain and spinal cord — is unable to drain from the brain.

More to Know

Everyone's brain and spinal cord float in a liquid called cerebrospinal fluid (CSF). CSF is produced in spaces within the brain called ventricles. Normally, it flows from the ventricles to the outer part of the brain and the spinal canal and then is recycled into the bloodstream. If a disease, injury, or other condition interferes with this recycling, the fluid can build up inside the brain.

This buildup of extra CSF inside the brain under pressure is called hydrocephalus. Abnormal pressure inside the head can cause headaches, vomiting, nausea (in older kids), and changes in behavior. It can damage the brain and interfere with its growth and development. In a young child it can cause the head to grow bigger. If the pressure gets very high, hydrocephalus can be life threatening.

Keep in Mind

When treated at the right time and with good medical care, hydrocephalus can be well controlled. To relieve the pressure, doctors may perform a type of surgery so the CSF flows out of the brain's ventricles and into another part of the body (for example, a ventriculoperitoneal [VP] shunt leads the fluid into the belly).

Surgery cannot cure the underlying cause of the hydrocephalus, but can treat the symptoms by decreasing the pressure inside the head.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.