What is Hydrocephalus?
Hydrocephalus is commonly known as 'water on the brain'. A watery fluid, known as cerebro-spinal fluid or CSF, is produced constantly inside each of the four spaces or ventricles inside the brain. The CSF normally flows through narrow pathways from one ventricle to the next, then out over the outside of the brain and down the spinal cord. The CSF is absorbed into the bloodstream and recirculates, and the amount and pressure are normally kept within a fairly narrow range. If the drainage pathways are blocked at any point, the fluid accumulates in the ventricles inside the brain, causing them to swell - resulting in compression of surrounding tissue. In babies and infants, the head will enlarge. In older children and adults, the head size cannot increase as the bones which form the skull are completely joined together.
What causes Hydrocephalus?
The condition is caused by the inability of CSF to drain into the bloodstream. There are many reasons why this can happen:
Congenital Hydrocephalus
This means that hydrocephalus is present at birth. It is important to remember that this term does not imply that it is hereditary. Often the exact cause of congenital hydrocephalus cannot be determined.
Prematurity
Babies born prematurely are at risk of developing hydrocephalus. A baby born early is far more vulnerable than one which goes the full term since it is still developing. The area which lies just beneath the lining of the ventricles in the brain is particularly important - because of the activity in this area it has a plentiful blood supply. Its blood vessels are very fragile and can be easily burst if the baby suffers too large a swing in blood pressure or becomes severely ill from other causes.
If these complications do occur, then the baby is at risk of developing a haemorrhage from rupture of the fragile vessels. This can lead to a blood clot developing, which in some cases is big enough to break through the wall of the ventricle. Should the clot block the flow of CSF, the baby will develop hydrocephalus. The blockage may be temporary or permanent. Even if a blood clot does not develop, the blood cells from the haemorrhage can cause blockage.
Spina Bifida
Most babies born with
spina bifida have hydrocephalus. In addition to the lesion in the spinal cord, there are abnormalities in the structure of certain parts of the brain which develop before birth. This prevents proper drainage of the CSF. The increase in pressure due to this can also compress the abnormal parts of the brain even further.
Other forms
Brain haemorrhage, including those occurring in adults ("stroke"), can result in this type of post-haemorrhagic hydrocephalus.
Meningitis
This is an infection of the membranes covering the brain. The inflammation and debris from this infection block the drainage pathways resulting in hydrocephalus. Meningitis can occur at any age but it is more common in children. The incidence of one form, haemophilus meningitis, has been drastically reduced by HIB vaccine.
Dandy Walker Cysts
There is a particular group of disorders involving the formation of fluid-filled cysts in the CSF system (for example Dandy Walker cysts). In these cases, hydrocephalus is often due to pressure on the surrounding tissues by the enlarging cyst.
Tumours
Tumours of the brain cause compression and swelling of surrounding tissues, resulting in poor drainage of CSF. In the treatment of brain tumours, it is often necessary to include measures to control hydrocephalus, which might only be temporary.
Genetic
In very rare circumstances, hydrocephalus is due to hereditary factors, which might affect future generations.
Other causes
There are many other very rare causes of hydrocephalus.
How is Hydrocephalus Treated?
Some forms of hydrocephalus require no specific treatment. Other forms are temporary and do not require long-term treatment. However, most forms do require treatment, and this is usually surgical. Drugs have been used for many years but they may have unpleasant side effects and are not often successful.
The usual treatment is to insert a shunting device. It is important to note that this does not 'cure' the hydrocephalus and damage to the brain tissue remains. Shunting controls the pressure by draining excess CSF, so preventing the condition becoming worse. Symptoms caused by raised pressure usually improve but other problems of brain damage will remain.
An alternative treatment may be third ventriculostomy. This treatment, if successful, avoids the need for a shunt. However, not all types of hydrocephalus can be treated by this method and it is not available in all neurosurgical units.
What is a Shunt?
A shunt is simply a device which diverts the accumulated CSF from the obstructed pathways and returns it to the bloodstream. It consists of a system of tubes with a valve to control the rate of drainage and prevent back-flow. It is inserted surgically so that the upper end is in a ventricle of the brain and the lower end leads either into the heart (ventriculo-atrial) or into the abdomen (ventriculo-peritoneal). The device is completely enclosed so that all of it is inside the body. The fluid which is drained into the abdomen passes from there into the bloodstream. Other drainage sites such as the outer lining of the lungs (ventriculo-pleural shunt) can also be used.
Possible Complications
In most cases, the shunts are intended to stay in place for life, though alterations or revisions might become necessary from time to time. The tube or catheter may become too short as the individual grows and an operation to lengthen it might be necessary.
Occasionally, as with any implant, there can be mechanical failure. Also, it is important to be aware that problems can occur with blockage or infection of the shunt.
What Symptoms Should be Looked for?
These vary enormously between individuals. Previous personal experience of a shunt problem is usually a reliable guide as to what to look for.
Possible signs of acute shunt blockage may include:
vomiting, headach, dizziness, photophobia (sensitivity to light) and other visual disturbances, drowsiness and fits.
Possible signs of chronic shunt blockage may include:
fatigue, general malaise, visuo-perceptual problems, behavioural changes, decline in academic performance, being just 'not right' from the carer's point of view.
Medical advice should be sought from your neurosurgical unit if a shunt blockage is suspected, within four hours of acute symptoms occurring.
In shunt infections, symptoms vary with the route of drainage.
In ventriculo-peritoneal shunts, the symptoms often resemble those of a blockage. This is because the shunt becomes infected and the lower catheter is very often then sealed off by tissue. There may be accompanying fever and abdominal pain or discomfort.
In ventriculo-atrial shunt infections, fever is present in most cases though often intermittently. Anaemia is frequently present, and sometimes skin rashes along with joint pains. In contrast to ventriculo-peritoneal shunts, such infections may not appear for months or years after the operation when they were contracted.
Various tests can be carried out for shunt infections and medical advice should always be sought if an infection is suspected.
How are shunt problems treated?
Shunt blockages which are causing illness usually require an operation to replace or adjust the offending part of the shunt. Shunt infections are usually treated by removal of the whole shunt and a course of antibiotics before insertion of a new system. Modern approaches to antibiotic therapy mean that such treatment can be expected to succeed in most cases.
More information on hydrocephalus and shunts.
Hydrocephalus and fits
Richard Hayward, consultant neurosurgeon, writes:
"Patients with hydrocephalus sometimes have fits. The fits are not due to the hydrocephalus itself but are usually associated with an underlying cause (meningitis, abnormal development of the brain, neonatal haemorrhage etc).
"As a general rule, fits in patients with hydrocephalus should be treated in the same way as those that occur in children who do not have hydrocephalus."
What are the effects of hydrocephalus?
There can be learning difficulties associated with hydrocephalus such as problems with concentration, reasoning and short-term memory. Hydrocephalus can also result in subtle effects: giving problems with co-ordination, motivation and organisational skills. Physical effects such as visual problems, or early puberty in children, may also occur.
Many of these effects can be overcome with teaching strategies or treatment where relevant.
It must be stressed that the effects of hydrocephalus vary from one individual to another and some people will have very few, if any, problems.
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