Three-dimensional ultrasound in the assessment of fetal cerebellar transverse and antero-posterior diameters.

Fetal cerebellum scanning by prenatal ultrasound (US) is very important for early detection of fetal central-nervous-system anomaly, as well as for the determination of gestational age (GA). Due to the small organ size and the unique shape of the fetal cerebellum (CL), accurate measurement of the dimensions of CL by two-dimensional (2-D) US is not easy if the appropriate plane cannot be reached. With the advent of three-dimensional (3-D) US, the disadvantages of 2-D US in assessing the fetal CL dimensions can be avoided. The purpose of this study was to assess the fetal cerebellar transverse diameter (CTD) and cerebellar antero-posterior diameter (CAD) using 3-D US. First, we compared the reproducibility of 2-D and 3-D US on the assessment of fetal cerebellar dimensions. Second, we prospectively measured CTD and CAD in 223 healthy fetuses using a cross-sectional design with an attempt to establish the normal growth charts of fetal CL. Our results showed 3-D US is superior to 2-D US in the reproducibility test of fetal cerebellar dimensions. In addition, with GA as the dependent variable, polynomial regression analysis showed that the best-fit equations for both CTD vs. GA and CAD vs. GA were the first-order. The best-fit predictive equation of GA by CTD was GA (week) = 9.0281 + 0. 58533 x CTD (mm) (r = 0.95, n = 223, SE = 1.82 weeks, p < 0.0001), and the best-fit predictive equation of GA by CAD was GA (week) = 10. 855 + 1.1672 x CAD (mm) (r = 0.82, n = 223, SE = 3.41 weeks, p < 0. 0001). Furthermore, all the correlation coefficients of CTD or CAD vs. the common fetal growth indexes were also highly significant (all p < 0.0001). In conclusion, our data of fetal CL dimensions assessed by 3-D US may serve as a useful reference in assessing fetal CL growth, dating GA or detecting fetal CL anomalies.