Which threshold is commonly used to diagnose ventriculomegaly?

• A. 4 mm
• B. 20 mm
• C. 2 mm
• D. 10 mm

Answer: (D)

Ventriculomegaly is diagnosed by measuring the width of the lateral ventricle at the atrium on a fetal brain ultrasound. The commonly used threshold is a transverse atrial width of 10 millimeters or greater. This cutoff reflects that normal atrial widths are typically under 10 mm, so reaching or exceeding 10 mm indicates dilation that may signal hydrocephalus or other anomalies. When performing the measurement, ensure you use the correct axial plane at the level of the atrium and place calipers perpendicular to the inner skull, avoiding the choroid plexus. Mild cases may hover around 10–12 mm, with larger values indicating more pronounced ventriculomegaly. Smaller values, like 4 mm or 2 mm, are generally normal, while a width around 20 mm would be a much more severe dilation.