OBJECTIVETo evaluate the third plane image of the three-dimensional sonography (3D US) for the quantitative analysis of the cerebellar vermis in normal and Dandy-Walker syndrome (DWS) fetuses.

METHODSThe cerebellar vermis was scanned with trans-abdominal 3D US in the second and third trimesters in 571 normal fetuses and 39 fetuses with Dandy-Walker syndrome. The surface area of the vermis in the mid-sagittal view was measured and calculated. The correlation between the vermian area and the pregnant week was analyzed. The data of vermian area between normal and DWS fetuses was compared.

RESULTSThe vermian area was measured in 529 normal fetuses in the third plane of 3D US. The vermis grew in a linear fashion throughout pregnancy and the growth pattern positively correlated with the gestational age (r2 = 0. 854, P < 0.05). In 39 fetuses with DWS, including 14 with Dandy-Walker malformation (DWM) and 25 with Dandy-Walker variant (DWV), no vermian structure was showed in the mid-sagittal plane in 12 fetuses with DWM and 2 fetuses with DWV, whereas a small vermis appeared in other DWSs.

CONCLUSIONSThe third plane image obtained by 3D US is valuable in studying the fetal cerebellar vermis during the middle and late pregnancy. Knowledge of normal and abnormal vermian appearance may help identify developmental anomalies. Measurement of vermian area in the third plane with 3D US provide a quantitative indicator for prenatal diagnosis of DWS.