PURPOSE: We evaluated the role of magnetic resonance (MR) imaging in the diagnosis of corpus callosum agenesis - isolated or associated with other anomalies - in fetuses with mild cerebral ventriculomegaly, as depicted at prenatal sonography. MATERIAL AND METHODS: Between January 2005 and March 2007, 33 fetuses with a mean gestational age of 28.9 weeks (range 17-37) and mild ventriculomegaly diagnosed at prenatal sonography were included in this prospective study. All fetuses underwent MR imaging according to the following protocol: half-Fourier T2-weighted images along the three orthogonal plane according to the longitudinal axis of the mother, and subsequently three orthogonal planes were acquired according to the fetal brain. Quantitative image analysis included the size of the transverse diameter of the lateral ventricles, in the axial plane, and the thickness of the adjacent cerebral cortex. Qualitative image analysis included morphology of the lateral ventricles (normal, parallel pattern colpocephaly), signal intensity changes of the fetal brain, interruption of the germinative matrix, agenesis of the corpus callosum (complete/partial) and associated malformations. Postnatal physical examination and diagnostic imaging, as well as surgery, were the standard of diagnosis. RESULTS: Mean axial diameter of the lateral ventricle was 11.6 mm (range 10-15 mm), and mean thickness of the adjacent cerebral cortex was 2.1 mm (range 1.8-3 mm); 23/33 fetuses (70%) showed normal morphology of the lateral ventricles, and 8/33 (24%) showed abnormal morphology (parallel pattern, colpocephaly). The entire corpus callosum was visualised in 20/33 fetuses (60%). In 8/33 fetuses (25%), partial agenesis was diagnosed, whereas in 5/33 (15%), there was hypogenesis. In 6/13 fetuses (46%), isolated corpus callosum agenesis was detected, and two cases of hypogenesis of the corpus callosum were misinterpreted - overestimated in one case and underestimated in another. CONCLUSIONS: MR imaging may prove to be a useful second-line imaging modality in the prenatal diagnosis of corpus callosum agenesis in fetuses with mild ventriculomegaly.
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