What is Hydrocephalus?

By , BSc

Hydrocephalus refers to a build-up of fluid within the brain. This accumulated fluid places increased pressure on the brain, which can cause brain damage.

Although hydrocephalus has sometimes previously been referred to as “water on the brain,” the fluid that accumulates in the brain is not water. The fluid is cerbrospinal fluid (CSF), a colorless, clear fluid that contains glucose and is more viscous than water. Around 500 ml of CSF is produced in our brain cavities each day. It circulates around the sub-arachnoid space that surrounds the brain and spinal cord and flows through cavities in the brain called ventricles and channels referred to as foramina. CSF cushions the brain by acting as a shock absorber as well as providing the brain with nutrients and removing waste products. Only around 120 to 150 ml of CSF can be contained in the brain at any given time, so any excess CSF moves into the bloodstream via valves referred to as the arachnoid villi.

Hydrocephalus can develop if too much CSF is produced, if the flow of CSF becomes blocked or if a problem arises with the arachnoid villi that prevents CSF being drained into the bloodstream. If any of these occur, the brain ventricles and sub-arachnoid space start to swell as the increased fluid causes pressure to build. If the problem is not promptly treated, the result can be permanent brain injury.

Types of hydrocephalus

There are three main types of hydrocephalus. The first type is present at birth and is referred to as congenital hydrocephalus. It can be caused by birth defects such as spina bifida or as a consequence of events that may occur during fetal development such as infection.

The second type develops at the time of birth or at some point after birth and is referred to as acquired hydrocephalus. This can develop at any age and may develop as the result of an injury or as a complication of disease, for example. Damage caused to the brain by such events results in enlarged brain ventricles that fill with excess CSF or blockages that prevent CSF being drained into the bloodstream.

The third type can affect individuals of any age, but is most commonly seen in people aged 50 years or older. It is called normal pressure hydrocephalus (NPH) and can develop as a consequence of events such as stroke, head injury, tumor, infection or complications after surgery.


This brain damage can lead to various different symptoms. Some of the main symptoms of hydrocephalus include:

  • Headache, neck pain
  • Nausea and vomiting
  • Blurred or double vision
  • Confusion

Some individuals may also experience:

  • Poor coordination
  • Difficulty with balance
  • Difficulty walking
  • Urinary and/or bowel incontinence

Individuals with hydrocephalus may not experience all of these symptoms, but they usually develop more than one of them.

In cases of NPH, the accumulation of CSF may be gradual and symptoms may develop slowly over a period of months or years. The most commonly occurring symptoms are difficulty walking, incontinence and problems with processing information.

The symptoms of congenital hyrdocephalus usually appear early on in childhood and typically include muscle spasms, an unusually large head size, irritability, difficulty feeding and drowsiness.


The main approach to diagnosing hydrocephalus is a brain scan, which may be a computerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan. The scans are used to look for any build up of CSF and signs of increased pressure in the brain. A doctor may also perform a physical assessment to evaluate symptoms, an eye test to check for any swelling behind the eye caused by pressure building up in the brain and a lumbar puncture to extract CSF and check the pressure level.

A lumbar puncture involves inserting a needle between two lumbar (lower back) vertebrae and into a space where CSF is contained. A small amount of CSF is removed via a syringe and the pressure is checked. After the lumbar puncture, the patient is assessed to see whether removing the CSF has improved their symptoms.


Hydrocephalus is usually treated using a device called a shunt, which is a thin tube that is surgically implanted in the brain to provide a channel by which excess CSF can be drained away from the brain. The fluid moves way from the brain to another body part, usually the abdomen, where it is then absorbed into the bloodstream. A full recovery is possible when patients are treated with a shunt.

Occasionally, adults with hydrocephalus are treated using a procedure referred to as third ventriculostomy. Here, a small hole is made beneath the third brain ventricle, which allows CSF to bypass a point of blockage.

Last Updated: Sep 17, 2015

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