Neuroimaging of ventriculomegaly in the fetal period.

Fetal cerebral ventriculomegaly (VM) is defined as an enlargement of the lateral ventricles of the developing fetal brain. It is diagnosed when the width of one or both lateral ventricles, measured at the level of the atrium, is ≥10 mm. VM is defined as mild when the atrial width is 10-15 mm and severe when >15 mm. VM is a non-specific sonographic sign which is common to various pathological conditions. It is frequently associated with neural and extraneural anomalies. The rate of associated malformations is higher (≥60%) in severe VM and lower (about 40%) in cases of mild VM. When an abnormality is associated with severe VM the incidence of aneuploidies is high (>15%); in isolated mild VM the mean value of aneuploidy is 2.7%. The rate of infections in severe VM is 10-20%, in mild forms 1-5%. Since the prognosis in cases of VM depends mainly on the associated anomalies, a careful examination of the fetus, particularly of the brain, is mandatory. Magnetic resonance imaging can be a useful diagnostic tool complementary to ultrasound in order to recognize subtle brain anomalies, such as neuronal migration and proliferation disorders.