Antenatal unilateral hydrocephalus

Fetal ventriculomegaly usually involves both lateral ventricles. If dilatation of the dependent lateral ventricle is seen, it might be assumed that the condition is bilateral and symmetric and that reverberation artifact is obscuring the ventricle nearer to the transducer. However, unilateral hydrocephalus can occur, though rarely and usually as a result of unilateral obstruction of the foramen of Monro. Careful attention to visualization of the obscured hemisphere is emphasized. In the patient described here the condition was associated with frontoethmoidal encephalocele.