Volumetric analysis of the germinal matrix and lateral ventricles performed using MR images of postmortem fetuses.

BACKGROUND AND PURPOSE The volumetric changes of the ventricular system and germinal matrix are important to understand brain maturation and the mechanism of subependymal hemorrhage. Our purpose was to show the 3D configuration of the brain, germinal matrix, and lateral ventricles and to discuss the volumetric changes of each structure with maturation by using high-resolution MR imaging. METHODS Three-dimensional MR images of 13 formalin-fixed fetal brains ranging from 7 to 28 weeks' gestational age (GA) were obtained on a 4.7-T unit. Each 3D configuration of the brain surface, germinal matrix, and ventricles was rendered from the cross-sectional imaging data sets and its volume measured. RESULTS The germinal matrix was detected on MR images at 9 weeks' GA. Its volume exponentially increased by 23 weeks' GA (maximum, 2346 mm3) and then sharply decreased at 28 weeks' GA. The volume of the lateral ventricles increased gradually and reached 2646 mm3 peak volume at 23 weeks' GA. Between 11 and 23 weeks' GA, total brain and germinal matrix volumes were exponentially increasing, but the volume ratio of germinal matrix to brain was stable at about 5%. On the other hand, the volume ratio of lateral ventricles to brain was large between 10 and 13 weeks' GA. This period corresponded to the lateral ventricle showing a "vesicular" aspect with a thin mantle, and the developing mantle thickness of the hemisphere resulted in the decreasing ratio. CONCLUSION Volumetric information concerning the germinal matrix and lateral ventricles may be useful in the accurate interpretation of clinical echograms and MR images of the fetal brain in utero.