Most common cause of fetal ventriculomegaly is ?

Hydrocephalus is characterized by an increased CSF volume with progressive ventricular dilatation (ventriculomegaly). Obstructive or noncommunicating hydrocephalus/ventriculomegaly develops most commonly in children because of an abnormality of the aqueduct or a lesion in the 4th ventricle. Obstruction of the aqueduct is the single most common cause of fetal and neonatal hydrocephalus/ ventriculomegaly. Non obstructive or communicating hydrocephalus most commonly follows a subarachnoid hemorrhage, which is usually a result of intraventricular hemorrhage in a premature infant.