Hydrocephalus: The Causes
There are many reasons why Hydrocephalus may occur:
» 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 that 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.
» Congenital Hydrocephalus
This means hydrocephalus is present at birth. It is important to remember that this term does not imply that it is hereditary. The exact cause of congenital Hydrocephalus cannot always be determined.
Babies born prematurely are at risk of developing Hydrocephalus. The brain of a baby born early is far more vulnerable than one that goes to 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 very plentiful blood supply. Its blood vessels are very fragile and can easily burst if the baby suffers too large a swing in blood pressure or in the amount of fluid in the system.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.
» Brain Haemorrhage
Other forms of brain haemorrhage, including those occurring in adults ('stroke') can result in this type of post-haemorrhagic Hydrocephalus
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 can be benign or malignant. 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 control Hydrocephalus, which might only be temporary.
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, and sometimes it is unknown why it has happened.