Mild Ventriculomegaly on Prenatal Ultrasound

Mild ventriculomegaly (atrial width between 10 mm to 20 mm) can be seen in association with the following conditions and should prompt close evaluation of the posterior fossa.

• Chiari II malformation: Important to recognize due to the high association with open neural tube defects. Inspection of the posterior fossa will reveal a small posterior fossa with effacement of the cisterna magna and a banana-shaped cerebellum. The lemon sign (flattened or inwardly scalloped frontal bones) is a less specific finding.
• Dandy-Walker: Hypogenic cerebellar vermis and communication of the cisterna magna with the 4th ventricle.
• Agenesis of the corpus callosum: Look for tear-drop shaped lateral ventricles.
• Infection:
• Chromosomal abnormalities:
• Isolated ventriculomegaly: