Three-dimensional volumetric study with VOCAL in normal and abnormal posterior fossa fetuses.

Purpose: The aim of this study was to compare volumetric parameters in the abnormal and normal posterior fossa using the Virtual Organ Computer-aided AnaLysis (VOCAL™) technique to determine whether fetuses with an abnormal posterior fossa have different volumes. Methods: A prospective study was conducted on 17 fetuses with an abnormal posterior fossa including, Dandy Walker malformation (DWM) ( n  = 6), vermian hypoplasia (VH) ( n  = 3), mega cisterna magna (MCM) ( n  = 8), and 99 healthy control fetuses from 20 to 34 weeks' gestation. Measurement of the fetal cisterna magna and cerebellar volume was performed in the standard transcerebellar plane through the VOCAL™ method. To establish the correlation of volumes with gestational age, polynomial regression analysis was performed. For comparison between groups, univariate ANCOVA was performed using gestational age as a covariate. The reliability was analyzed by the intraclass correlation coefficient (ICC). Results: Cerebellar volume and cisterna magna volume were correlated with gestational age. Posterior fossa volume was significantly larger in DWM ( p  < .0001) and MCM ( p  < .0001) in comparison to the control group. In VH group, cisterna magna volume does not seem to expand ( p  = .298). Cerebellar volume does not seem to change in subgroups when the influence of gestational age is discarded ( p  = .09). The ratio of cerebellar volume to the cisterna magna volume decreases significantly in abnormal fetuses ( p  < .0001). Good intraobserver and interobserver reliabilities were found for both cerebellum and cisterna magna measurements. Conclusions: Volume analysis may have a role in discrimination of different posterior fossa pathologies.