Hydrocephalus is a build up of fluid inside the skull, leading to brain swelling. Hydrocephalus means "water on the brain."

Hydrocephalus is due to a problem with the flow of cerebrospinal fluid (CSF), the liquid that surrounds the brain and spinal cord. The fluid brings nutrients to the brain, takes away waste from the brain, and acts as a cushion.

CSF normally moves through areas of the brain called ventricles, then around the outside of the brain and the spinal cord. It is then reabsorbed into the bloodstream.. Build up of CSF can occur in the brain if it's flow or absorption is blocked, or if too much CSF is produced.

This build up of fluid puts pressure on the brain, pushing the brain up against the skull and damaging or destroying brain tissues.

Hydrocephalus may start while the baby is growing in the womb. It is commonly present with myelomeningocele , a birth defect involving incomplete closure of the spinal column. Genetic defects and certain infections that occur during pregnancy may also cause hydrocephalus.

In young children, hydrocephalus may also be associated with the following conditions:

• Infections that affect the central nervous system (such as meningitis or encephalitis ), especially in infants
• Bleeding in the brain during or soon after delivery (especially in premature babies)
• Injury before, during, or after childbirth, including subarachnoid hemorrhage
• Tumors of the central nervous system, including the brain or spinal cord
• Injury or trauma

Hydrocephalus most often occurs in children, but may also occur in adults and the elderly. See: Normal pressure hydrocephalus