Hydrocephalus

Definition:

A disorder associated with excessive fluid in the brain.

Causes, incidence, and risk factors:

The fluid in the brain (cerebrospinal fluid or CSF) is formed in the brain. CSF usually circulates through parts of the brain, its covering, and the spinal canal, and is then absorbed into the circulatory system.

When the circulation or absorption of this fluid is blocked, or excessive fluid is produced, the volume of fluid in the brain becomes higher than normal. The accumulation of fluid puts pressure on the brain forcing it against the skull and damaging or destroying the tissues.

Symptoms vary depending on the cause of the obstruction to CSF circulation, the age at which the problem develops, and the extent of damage to brain tissue caused by the hydrocephalus.

In infants, fluid accumulates in the central nervous system, causing the fontanelle (soft spot) to bulge and the head to expand. The head can enlarge because the bony plates which make up the skull have not yet fused together. However, once the skull bones are completely fused together, at about age 5, the skull will no longer expand.

In small children, risks for developing hydrocephalus include congenital defects, tumors of the central nervous system, intrauterine infection, infections in an infant or child that affect the central nervous system (such as meningitis or encephalitis), injury occurring during the birth process, or trauma before or after birth (including subarachnoid hemorrhage). Myelomeningocele, a disorder involving incomplete closure of the spinal column, is strongly associated with hydrocephalus.

In older children, risks include history of congenital or developmental defects, space-occupying lesions or tumors of the brain or spinal cord, central nervous system infections, bleeding anywhere in the brain, and trauma.

The incidence is approximately 1 out of 1,000 people. Hydrocephalus most often occurs in children, but may also occur in adults and the elderly.

See Normal pressure hydrocephalus (NPH).