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 but known causes can include: 

Aqueduct Stenosis: 
One of the pathways (aqueduct) linking the ventricles in the brain is narrowed (stenosis) which prevents flow of CSF. Although always congenital, symptoms may not occur until sometime later. 

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. For further information about spina bifida, see Shine’s Information Sheet: What is spina bifida?

Cysts within the brain: 
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. 

Genetics:
 In very rare circumstances, hydrocephalus is due to hereditary factors, which might affect future generations, such as x-linked hydrocephalus. 

Maternal infections:
 These include group B streptococcus which can cause neonatal meningitis and toxoplasmosis in the pregnant woman. Both are rare but can cause hydrocephalus.