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 th e determination of gestational age (GA). Due to the small organ size and th e unique shape of the fetal cerebellum (CL), accurate measurement of the di mensions of CL by two-dimensional (2-D) US is not easy if the appropriate p lane 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 d iameter (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 C AD 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 dimen sions. In addition, with GA as the dependent variable, polynomial regressio n analysis showed that the best-fit equations for both CTD vs. GA and CAD v s. GA were the first-order. The best-fit predictive equation of GA by CTD w as GA (week) = 9.0281 + 0.58533 x CTD (mm) (r = 0.95, n = 223, SE = 1.82 we eks, 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, t he 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 se rve as a useful reference in assessing fetal CL growth, dating GA or detect ing fetal CL anomalies. (C) 2000 World Federation for Ultrasound in Medicin e & Biology.