Topic Overview

Hydrocephalus of the brain occurs when there is an imbalance in how much cerebrospinal fluid (CSF) is made and absorbed, or in how it flows. One way to classify this condition is by how the imbalance occurs. There are two main ways:

• Nonobstructive, or communicating, hydrocephalus occurs when the CSF flows out of the chambers of the brain (ventricles) and into the spinal canal, but it is not reabsorbed normally by the tissue surrounding the brain and spinal cord. Sometimes this type of hydrocephalus corrects itself.
• Obstructive, or noncommunicating, hydrocephalus occurs when the CSF does not flow properly between or out of the brain ventricles because of an obstruction, such as from a malformation or narrowing.

In very rare cases the brain tissue makes too much CSF and the body can't properly absorb or distribute the high amount of fluid. This is called overproduction hydrocephalus.

Cerebrospinal fluid sometimes builds up rapidly, such as with an injury, and can cause sudden and severe damage if not treated. Other times the fluid gradually accumulates and may not cause problems right away.

Types of hydrocephalus include:

• Congenital hydrocephalus, which is present at birth. Congenital hydrocephalus may be caused by physical problems with how CSF flows or is made or absorbed, by infections or trauma during fetal development, or by teratogens. It may be linked with other birth defects that affect the spine, especially open neural tube defects.
• Acquired hydrocephalus, which develops at the time of birth or later. It can be caused by infections such as meningitis, bleeding, injury, or a tumor.
• Normal-pressure hydrocephalus, which usually develops in people who are age 55 or older. It is a potentially treatable cause of dementia. This type of hydrocephalus often occurs after head trauma, infections, and bleeding within the brain.
• Ex-vacuo hydrocephalus, which occurs when there is damage to the brain caused by stroke or traumatic injury. This type of hydrocephalus may not be a health danger for some people, in which case treatment is not needed.

With all types of hydrocephalus, early detection and treatment are important to minimize or prevent long-term problems.