Fetal Ventriculomegaly

The term ventriculomegaly refers to enlargement of the ventricles of the central nervous system. Measurement of the atrium of the lateral ventricle is an accurate way of assessing the integrity of the ventricular system prenatally. The normal mean dimension of the lateral ventricular atrium ranges from 6 to 8 mm beginning at 15 weeks through term-gestational age. An atrial dimension >10 mm is above 2.5–4 SD of the mean [1, 2]. Therefore, fetal ventriculomegaly is defined by enlargement of the lateral ventricular atrial dimension above 10 mm at any gestational age [3, 4]. Fetal ventriculomegaly can be unilateral or bilateral. Asymmetry in atrial diameter should only be considered abnormal if at least one atrial measurement is above 10 mm [5]. Fetal ventriculomegaly can be further classified as mild (10–12 mm), moderate (13–15 mm), and severe (above 15 mm) with increased risk of associated abnormalities and abnormal outcome with higher degrees of ventricular dilatation [3, 6, 7]. When ventriculomegaly is the only abnormal CNS finding, it has been referred to as “isolated ventriculomegaly” [3]. Mild isolated ventriculomegaly can be a normal variant [6, 8].