Fetal mild idiopathic lateral ventriculomegaly: is there a correlation with fetal trisomy?

Mild idiopathic lateral ventriculomegaly in the mid‐trimester fetus can be accurately detected using modern prenatal ultrasonography. Since an abnormal karyotype has been reported in some of these cases, the present prospective study was designed to evaluate, first, the prevalence of mild idiopathic lateral ventriculomegaly in the general obstetric population and, second, to determine the incidence of abnormal fetal karyotype associated with mild idiopathic lateral ventriculomegaly. Eight cases of mild idiopathic lateral ventriculomegaly (0.15%) were detected among 5400 routine prenatal sonographic examinations, between 16 and 22 weeks' gestation. Three newborn infants were found to be normal; in one baby, spontaneous resolution of the lesion occurred in utero, and, among the other five cases, two had an abnormal karyotype: one had Down's syndrome, and one trisomy 18. A review of the English literature revealed that 12% of fetuses with mild idiopathic lateral ventriculomegaly have an abnormal karyotype. Since 3% of the fetuses with Down's syndrome can be visualized in utero with mild idiopathic lateral ventriculomegaly, the calculated risk for Down's syndrome when such lesions appear is about 3%. We, therefore, conclude that karyotypic study is warranted in the mid‐trimester fetus with incidental findings of mild idiopathic lateral ventriculomegaly.