Hydrocephalus refers to an increase in the amount of cerebrospinal fluid in the cranium. The cerebrospinal fluid, or CSF, is like water. It is produced by cells near the brain, and it surrounds the brain and spinal cord. The fluid flows around the brain and down into the spinal canal. Normally it is absorbed at the same rate it is produced, so that there is no net gain in fluid. In hydrocephalus, however, the fluid builds up either because it is blocked (by a tumor, cyst, or other mass) or because it cannot be absorbed fast enough.

Buildup of spinal fluid can cause increased pressure on the brain. Symptoms can include headaches, blurred vision, nausea, and vomiting. In severe cases, this can progress to confusion, lethargy, and possibly coma and death if not treated. Not all forms of hydrocephalus present with these symptoms, however.

Treatment involves diverting the spinal fluid out of the head, usually into the abdominal cavity. The lining of the abdominal wall absorbs the fluid. This is called a VP shunt (ventriculoperitoneal shunt: a shunt from the ventricle to the peritoneum). A small catheter and tubing system is tunneled under the skin, and a valve controls the amount of flow.

In some cases, the flow of cerebrospinal fluid can be restored by opening up membranes through a small scope (endoscope) inserted through a small hole in the skull. In these cases, the need for a permanent shunt can be avoided.