Hydrocephalus is a pathological increase in intracranial cerebrospinal fluid, usually within the lateral ventricles and often, although not always, associated with an increase in intracranial pressure and an abnormally large biparietal diameter. Ventriculomegaly simply means enlargement of the lateral cerebral ventricles. The reported incidence of hydrocephalus at birth is 0.5–3 per 1000. The incidence of ventriculomegaly diagnosed antenatally by ultrasound (atrium 10–15mm), varies from 1.48 per 1000 (8/5400) to 22 per 1000 (11/500), the latter study being in a low risk population.