Overview of Hydrocephalus
The word hydrocephalus is derived from two Greek words, hydro, meaning water, and cephalus, meaning head, and once was called "water on the brain." Hydrocephalus is the condition caused by the accumulation of an abnormally large amount of cerebrospinal fluid (CSF) in the skull, or cranium. Normally, CSF flows continually from the interior cavities in the brain (ventricles) to the thin subarachnoid space that surrounds the brain and spinal cord.
About a pint of this clear fluid is produced a day and is absorbed by the blood stream.
CSF performs the following functions:
- Balances the amount of blood in the head.
- Bathes and protects the brain and spinal cord.
- Carries nutrients between the brain and spinal cord while removing waste.
Normal flow and absorption through the subarachnoid space is dependent on proper CSF pressure in the head (called intracranial pressure). A build up of CSF often causes a dangerous increase in pressure. The combination of CSF buildup and the subsequent increase in intracranial pressure can stress brain tissue and can cause the characteristic symptoms of hydrocephalus, though they also may occur with normal pressure.
Incidence and Prevalence of Hydrocephalus
Congenital hydrocephalus affects about one in every 1000 births. The overall prevalence in the United States is about 0.5%. Most cases are detected early, either at or soon after birth. The incidence of acquired hydrocephalus in adults is not known because it occurs as a result of injury, illness, or environmental factors.
Types of Hydrocephalus
The two main types of hydrocephalus are congenital (developed before birth) and acquired (developed during or after birth). Hydrocephalus is further classified as communicating and noncommunicating.
In communicating hydrocephalus, the obstruction occurs in the subarachnoid space. Noncommunicating hydrocephalus means the obstruction is located within the ventricles. Intracranial pressure is usually increased and significant neurological abnormalities may develop, including damage to brain tissue. This type is most commonly caused by stroke or traumatic brain injury.
Normal pressure hydrocephalus (NPH) is more common in patients over the age of 60. In NPH, obstruction develops over time, slowly enlarging the ventricles and increasing pressure in the brain. NPH usually affects areas of the brain that control the bladder, movement in the legs, and cognitive abilities (e.g., memory, reasoning, problem solving).