The "vermian-crest angle": does it allow accurate categorisation of fetal upward rotation of cerebellar vermis on intrauterine MRI? A pilot study.

AIM: To test a new parameter to assess the position of the fetal cerebellar vermis in the posterior fossa (PF) using intrauterine magnetic resonance imaging (MRI). MATERIALS AND METHODS: The angle between the cerebellar vermis and the internal occipital crest (vermian-crest angle, VCA) was assessed retrospectively using MRI in fetuses with and without PF anomalies. Spearman's rank test was used to investigate correlation of the VCA with gestational age (GA). Groups were compared using Student's t-test and the one-way analysis of variance (ANOVA) with the Bonferroni adjustment. Box-and-whisker plots were also used. RESULTS: One hundred and two normal cases were identified. Mean±SD GA at MRI was 26.5±2.8 weeks (range: 22-32 weeks). The VCA was 64.49±11.5° independently of GA (r=0.19; p=0.12). In addition, 30 fetuses at 19-28 weeks were identified with Blake's pouch cyst (BPC; n=5), Dandy-Walker malformation (DWM; n=12), mega cisterna magna (MCM; n=10), and vermian hypoplasia (VH; n=3). The VCA was significantly different in the DWM (p<0.001) and BPC (p<0.001) subgroups, but was not significantly different in cases of VH (p=0.84) and MCM (p=0.95) in comparison with controls. CONCLUSIONS: A new method to assess vermian position within the PF using intrauterine MRI was assessed. In combination with the other existing parameters, it may be helpful for addressing the categorisation of upward rotation of the fetal cerebellar vermis; however, further studies are necessary to strengthen the present findings.