Authors’ response to Letter from A. Toi: cerebellar vermis area versus perimeter

We would like to thank Dr Toi for his comments on our 2012 study, “Assessment of cerebellar vermis biometry at 18–32 weeks of gestation by three-dimensional ultrasound examination” [1]. The measurement of cerebellar vermis (CV) area reported in Figure 3B (not in Figure 5 as indicated in the letter, where the reproducibility was tested by Bland–Altman plots) are those resulting from manual tracing of the CV perimeter. Since the shape of the CV is not circular, but for the presence of the fastigium has a C shape, area cannot be calculated by using the formula 3.14 × CV length.

Finally, in the 2 years following the publication of these reference limits, we have tested them in 21 fetuses with postnatally or autopsy-confirmed cerebellar hypoplasia and found that CV length is the most efficient parameter.