An abnormal accumulation of CEREBROSPINAL FLUID, or CSF, within the skull, as a result of one or more of three main causes: (i) excessive CSF production; (ii) defective CSF absorption; (iii) blockage of the circulation of CSF. Such disturbances in the circulation of the fluid may be for congenital reasons (most commonly associated with SPINA BIFIDA), to MENINGITIS, or to a tumour.
In infants, the chief sign is the gradual increase in size of the upper part of the head, out of all proportion to the face or the rest of the body. The head is globular, with a wide anterior FONTANELLE and separation of the bones at the sutures with prominent scalp veins. The normal infant's head circumference should not increase more than 2·5 cm (1 inch) in each of the first two months of life, and much more slowly subsequently; growth beyond this rate should arouse suspicions of hydrocephalus; medical professionals caring for infants use charts for this purpose.
The cerebral ventricles are widely distended, and the convolutions of the brain flattened, while occasionally the fluid escapes into the cavity of the cranium, which it fills, pressing down the brain to the base of the skull. As a consequence of such changes, the functions of the brain are interfered with, and the mental condition of the patient is generally impaired. Untreated, the senses, especially vision, become affected as the disease advances, and sight is often lost, as is also hearing.
Numerous operations have been devised for the treatment of hydrocephalus. The most satisfactory of these utilise unidirectional valves and shunts (tubes), whereby the cerebrospinal fluid is bypassed from the brain into the right atrium of the heart or the peritoneal cavity. The shunt may have to be left in position indefinitely. Close follow-up is needed as shunts have a tendency to block, become displaced or become infected. In these circumstances, symptoms and signs may recur and shunt revision surgery become necessary, sometimes urgently.