An enlargement of the head resultingfrom excessive accumulation of cerebrospinal fluid within the ventricles (open spaces) of the brain (internal hydrocephaly) or, less often, between the hemispheres (external hydrocephaly).in most cases progressive accumulation of fluid produces internal pressure that damages the brain tissue. If the damage is slight, intellectual impairment is not great; if it is extensive, severe, or profound mental retardation may result, sometimes accompanied by convulsions and impairment or loss of sight and hearing. Most hydrocephalics require custodial care. The less severe cases can be trained to care for their physical needs, but where the head is extremely large and heavy they must be confined to bed.Hydrocephaly may be present at birth, and probably results from prenatal conditions that affect the formation and circulation of the cerebrospinal fluid. In rare cases, known as an- encephaly, the fluid completely inhibits the growth of the brain. In some instances the condition develops during infancy and early childhood in connection with intracranial neoplasms (tumors), head injury, or brain inflammations associated with chronic meningitis or congenital syphilis. The rare infectious disease, toxoplasmosis, may also result inhydrocephaly.Recently developed surgical techniques have been dramatically successful in arresting the condition in its early stages before severe brain damage occurs. These procedures are directed toward reducing the production of cerebrospinal fluid or channeling it past obstructions resulting from congenital malformations or postnatal infections. Some cases, however, develop severe postoperative complications or do not respond to treatment, and the cranium continues to expand until gross deterioration and death occur.