Hydrocephalus is a condition 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 of blood supply. Its blood vessels are very fragile and can 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 can compress the abnormal parts of the brain even further.
Other forms Forms of 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 the 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 developed due to the 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 may only be temporary.
Genetic In very rare circumstances, Hydrocephalus is due to hereditary factors, which may affect future generations.
(Source: International Federation for Spina Bifida and Hydrocephalus in Brussels, Belgium)