What does magnetic resonance imaging add to the prenatal sonographic diagnosis of ventriculomegaly?

OBJECTIVE: The purpose of this study was to determine the contribution of magnetic resonance imaging (MRI) in evaluating fetuses with the sonographic diagnosis of ventriculomegaly (VM).
METHODS: Over 4 years, consecutive fetuses with the sonographic diagnosis of VM at 1 facility who underwent prenatal MRI at a second facility were included. The roles of MRI and follow-up sonography were tabulated. The patients were analyzed in 2 groups based on the presence or absence of other central nervous system (CNS) abnormalities.
RESULTS: Twenty-six fetuses with a gestational age range of 17 to 37 weeks had sonographically detected VM (atria > or =10-29 mm), including 19 with mild VM (atria 10-12 mm). In group 1, 14 had isolated VM, 6 of which reverted to normal by the third trimester. Magnetic resonance imaging showed cerebellar hypoplasia not shown by sonography in 1 fetus and an additional finding of a mega cisterna magna in a second fetus. In group 2, 12 fetuses had VM and other CNS anomalies on sonography. Additional findings were seen with MRI in 10 of these fetuses, including migrational abnormalities (n = 4), porencephaly (n = 4), and 1 diagnosis each of abnormal myelination, hypoplasia of the corpus callosum, microcephaly, a kinked brain stem, cerebellar hypoplasia, and congenital infarction. There were significantly more fetuses with additional CNS anomalies found by MRI among those in group 2 compared with those in group 1 (Fisher exact test, P = .001).
CONCLUSIONS: Although sonography is an accurate diagnostic modality for the evaluation of fetuses with VM, MRI adds important additional information, particularly in fetuses in whom additional findings other than an enlarged ventricle are seen sonographically.