Mild ventriculomegaly (VM), also defined as “borderline”, is a condition characterized by an atrial width between 10 and 15 mm independently from gestational age.
Fetuses with mild ventriculomegaly require an accurate morphological examination to rule out for associated neural and extraneural anomalies. The percentage of this association is 41%. However, in almost 13% of cases, the associated anomaly is not recognized at the time of the initial presentation. It is important to monitor the atrial width during the third trimester because in 15% of the cases it increases. Most of the cases missed at the first examination have a late onset diseases (migrational disorders, parenchimal damage, hemorrhage, etc). For these conditions MRI may play a useful role.
Maternal serum tests for congenital infections should be performed, since infections may be the cause of mild VM in 1.5% of the cases.
Fetal karyotype should also be evaluated, since chromosomal abnormalities may be associated in 2.8% of the cases of isolated VM.
The counseling in cases of apparently isolated mild VMs focuses on the possibility of neurodevelopmental delay in the surviving infants. The average percentage of neurodevelopmental delay reported in the literature is 10.9%. The possibility of late onset brain anomalies must be considered.
In conclusion, the most important prognostic factors are the association with other abnormalities not detected at the first examination and the progression of the ventricular dilatation.
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