Hydrocephalus & Shunts
The term hydrocephalus is derived from the Greek words "hydro" meaning water and "cephalus" meaning head. As the name implies, it is a condition in which the primary characteristic is excessive accumulation of fluid in the brain. Although hydrocephalus was once known as "water on the brain," the "water" is actually cerebrospinal fluid (CSF) — a clear fluid that surrounds the brain and spinal cord. The excessive accumulation of CSF results in an abnormal widening of spaces in the brain called ventricles. Ventricles are hollow cavities within the brain that are constantly producing CSF. This widening creates potentially harmful pressure on the tissues of the brain.
The ventricular system is made up of four ventricles connected by narrow passages. Normally, CSF flows through the ventricles, exits into cisterns (closed spaces that serve as reservoirs) at the base of the brain, bathes the surfaces of the brain and spinal cord, and then reabsorbs into the bloodstream.
CSF has three important life-sustaining functions:
- To keep the brain tissue buoyant, acting as a cushion or “shock absorber”
- To act as the vehicle for delivering nutrients to the brain and removing waste; and
- To flow between the cranium and spine and compensate for changes in intracranial blood volume (the amount of blood within the brain).
The balance between production and absorption of CSF is critically important. Because CSF is made continuously, medical conditions that block its normal flow or absorption will result in an over-accumulation of CSF. The resulting pressure of the fluid against brain tissue is what causes hydrocephalus.
What are the types of hydrocephalus?
Hydrocephalus may be congenital or acquired:
- Congenital hydrocephalus is present at birth and may be caused by either events or influences that occur during foetal 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 non-communicating.
- Communicating hydrocephalus occurs when the flow of 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.
- Non-communicating 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 which do not fit exactly into the categories mentioned above and primarily affect adults: hydrocephalus ex-vacuo and normal pressure hydrocephalus
- Hydrocephalus ex-vacuo occurs when stroke or traumatic injury cause damage to the brain. In these cases, brain tissue may shrink.
- Normal pressure hydrocephaluscan happen to people at any age, but it is most common among the elderly. It may result from a subarachnoid haemorrhage, head trauma, infection, tumour, or complications of surgery. However, many people develop normal pressure hydrocephalus even when none of these factors are present for reasons that are unknown.
How is hydrocephalus treated?
Hydrocephalus is most often treated by surgically inserting a shunt system. This shunt system diverts the flow of CSF from the brain and spinal cord to another area of the body where it can be absorbed as part of the normal circulatory process.
A shunt system consists of the shunt, a flexible but sturdy plastic tube, a catheter, and a valve. One end of the catheter is placed within a ventricle inside the brain or in the CSF outside the spinal cord. The other end of the catheter is commonly placed within the abdominal cavity, but may be placed at other sites in the body depending on the patient’s situation. A valve located along the catheter maintains one-way flow and regulates the rate of CSF flow. Shunt systems may be permanent or temporary and may need to be replaced if they malfunction.