Ventriculomegaly is defined as the atrial width of the lateral ventricle exceeding which threshold on fetal ultrasound?

• A. 8 mm
• B. 10 mm
• C. 12 mm
• D. 15 mm

Answer: (B)

On fetal ultrasound, ventriculomegaly is identified when the lateral ventricle’s atrial width is larger than the upper limit of normal. The normal atrial width is about 10 mm, so any measurement greater than 10 mm defines ventriculomegaly. The measurement is taken in the axial view at the level of the atrium, from inner table to inner table. Mild ventriculomegaly is typically around 10–12 mm, moderate about 12–15 mm, and severe over 15 mm, but the defining threshold is simply anything exceeding 10 mm.