Hydrocephalus is best detected antenately by:

Hydrocephalus is a condition in which there is an abnormal increase in cerebrospinal fluid within the ventricular and subarachnoid spaces of brain. “The prenatal diagnosis of hydrocephalus is usually made by demonstration of a dilated ventricular system in an ultrasound examination.” Fernando Arias 2/e, p 331 Earliest and most accurate sonographic sign of hydrocephalus – Enlarged lateral ventricles. The lateral ventricle is measured at the level of atrium. Normal transverse diameter of atrium is 7 mm + 1 mm (It remains constant during the second and third trimester). When diameter of atrium is >10 mm, it is called as Ventriculomegaly/Hydrocephalus. Other signs of hydrocephalus on USG: Dangling choroid plexuses. Thinning out of cerebral cortex.