Why Does it Happen?

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.

Prematurity

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.