Mild ventriculomegaly is defined as being present when the width of the lateral ventricle, measured at the atrium, is greater than or equal to 10 mm (1-3). Sonographic technique is important when evaluating the ventricles. Care must be taken not to measure from the midline, but rather to use the medial aspect of the ventricle. Oblique planes should not be used to measure the ventricle.
Identification of a fetus with mild ventriculomegaly should prompt a diligent search for associated central nervous system (CNS) and extra-CNS anomalies, as many fetuses with ventriculomegaly have additional abnormalities. Fetuses with concurrent anomalies are at greater risk for an underlying chromosomal abnormality (4-6). Among cases of truly isolated mild ventriculomegaly, for which chromosome analysis was performed, approximately 2% (4,7) had a chromosomal abnormality. It should be noted that this data has been ascertained from populations of patients already at an increased risk for a fetal anomaly because of previous abnormal ultrasound findings, size and date discrepancy, abnormal maternal serum screen, twin gestation, placenta previa, advanced maternal age, and preterm labor; therefore, it is unclear how these risk figures apply to low-risk pregnancies.
Given the finding of fetal ventriculomegaly, we recommend offering genetic counseling, fetal echocardiography, amniocentesis, as well as follow-up ultrasound examination to search for additional anomalies and assess any progression of ventriculomegaly. A fetal MRI research protocol is currently ongoing at BIDMC and may be useful in identifying anomalies not readily visualized by sonography, such as agenesis of the corpus callosum, commonly associated with ventriculomegaly. The referring clinician should be notified at the time of the original scan to discuss these issues.
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