What are the different types of hydrocephalus?

Aria Fallah, MD
There are two main types of hydrocephalus. Non-communicating hydrocephalus is where the blockage of cerebrospinal fluid (CSF) is at the level of the fluid spaces of the brain. Communicating hydrocephalus where the blockage of CSF is at the surface of the brain.

Hydrocephalus may be congenital or acquired. Congenital hydrocephalus is present at birth and may be caused by events or influences that occur during fetal development, or genetic abnormalities. Acquired hydrocephalus develops at the time of birth or at some point afterward. This type of hydrocephalus can affect individuals of all ages and may be caused by injury or disease.

Hydrocephalus may also be communicating or noncommunicating. Communicating hydrocephalus occurs when the flow of cerebrospinal fluid (CSF) is blocked after it exits the ventricles. This form is called communicating because the CSF can still flow between the ventricles, which remain open. Noncommunicating hydrocephalus-also called obstructive hydrocephalus-occurs when the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles. One of the most common causes of hydrocephalus is aqueductal stenosis. In this case, hydrocephalus results from a narrowing of the aqueduct of Sylvius, a small passage between the third and fourth ventricles in the middle of the brain.

There are two other forms of hydrocephalus that do not fit exactly into these four categories and primarily affect adults-hydrocephalus ex-vacuo and normal pressure hydrocephalus (NPH).

Hydrocephalus ex-vacuo occurs when stroke or traumatic injury causes damage to the brain. In these cases, brain tissue may actually shrink. NPH can occur at any age, but it is most common among the elderly. It may result from a subarachnoid hemorrhage, head trauma, infection, tumor, or complications of surgery. However, for reasons that are unknown, many people develop NPH even when none of these factors are present.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.

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