In hydrocephalus there is an abnormal amount of cerebrospinal fluid within and around the brain, causing increased pressure in the skull. The term 'water on the brain' is sometimes used for this condition.

When the condition is congenital the pressure from accumulated fluid expands the babies skull, sometimes greatly because the bones are not rigid. This causes a typical appearance of an abnormally large vault to the skull. There may also be: Irritability; An inability to look upwards; Restricted eye movements; Loss of appetite; Vomiting; Seizures; A decreased level of consciousness and without treatment to death.

When the condition occurs in older children and adults it leads to headache, vomiting and damage to the cranial nerve function, including even blindness.

Causes

Hydrocephalus results when the fluid is produced faster than it can be reabsorbed. This is because the circulation of the fluid is obstructed by a defect present at birth (a congenital abnormality), particularly Spina bifida.

Or by a later acquired disease which may result from a brain infection (e.g. meningitis), from a tumour or from bleeding within the skull, due to brain injury.

Treatment

It is usually necessary to shunt, or by-pass, the normal channels by means of a tube passed into one of the spaces in the brain (ventricle). The tube is carried right down to open into the abdominal (peritoneal) cavity. Alternatively, the shunt tube can be carried down under the skin of the neck to be inserted, by way of a jugular vein, into the heart. In both cases, the tube contains a one-way valve so that fluid can pass out of the brain but not back in.