The brain and spinal cord are surrounded by cerebrospinal fluid (CSF). In the brain are a number of cavities, one of which contains a network of veins (the choroid plexus) that secretes the CSF, which passes through small ducts to the outside of the brain. From there it flows down and around the spinal cord in the back, from where it is absorbed into the blood. Hydrocephalus occurs when excess CSF accumulates in or around the brain. There are three types of hydrocephalus:-
- Obstructive hydrocephalus occurs if CSF cannot escape from the cavities within the brain due to a blockage in the draining tubes, and the brain is blown up by the fluid it contains.
- Communicating hydrocephalus occurs when there is a blockage of the circulation down the spinal cord and the fluid cannot be absorbed back into the bloodstream.
- Normal pressure hydrocephalus may occur in the elderly after a stroke, bleed into the brain or changes in brain structure with dementia.
The first two types are usually caused by a developmental abnormality of the foetus, or may develop in later life because of brain infections, tumours in the brain or skull, a colloid or other form of cyst in the brain, blood clots and other rarer conditions.
In babies with hydrocephalus, the soft skull is grossly dilated by the excess fluid. In older children or adults, a severe headache, personality changes, partial paralysis and loss of consciousness may be symptoms, as the harder skull is unable to expand. Other symptoms will depend upon the effect of the increased fluid pressure on the brain.
It is diagnosed by a CT or MRI scan.