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

Abstract

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.

fig 1.

T1-weighted MR image (left) reconstructed from 3D-SSFP sequence and sagittal H&E-stained photomicrograph (right) of fetal brain at 21 weeks' GA. There is good correlation between the images. Each image reveals the germinal matrix (arrows) and migrating neuroblast layer (arrowheads)

fig 2.

Images show good correlation between macroscopic brain (upper row) and 3D surface-rendered brain (middle row). Germinal matrix (orange), located ventrolateral to the lateral ventricles (blue), extends along the lateral walls of the lateral ventricles (lower row).

fig 3.

Successive images show developmental changes of lateral configuration of brain, germinal matrix, and ventricular system. The brain surfaces (upper row), germinal matrix (middle row, orange), and ventricular system (lower row, blue) of human fetal brain were reconstructed by surface rendering. The volume of the germinal matrix increased until 23 weeks' GA and decreased rapidly at 28 weeks' GA. Note how lateral ventricles change from fetal type, with vesicular aspect and bicornuate shape, to adult type with increasing GA.

fig 4.

Serial coronal MR images of the fetus at 7 weeks' GA. Germinal matrix cannot be detected

fig 5.

Serial coronal MR images of the fetus at 9 weeks' GA. Note germinal matrix is detected ventrolateral to the lateral ventricles (arrow)

fig 6.

Volumetric changes of the fetal brain (open triangles), germinal matrix (open circles), and lateral ventricles (solid circles). Increasing fetal brain volume (gray curve) has an exponential relationship (r² = .963) to GA, reaching 132.5 cm³ at 28 weeks' GA. The germinal matrix also increases exponentially, reaching a volume of 2.3 cm³ at 23 weeks' GA, then decreases rapidly after 25 weeks' GA. In contrast to the germinal matrix, the volume of the lateral ventricles gradually increases, up to 2.6 cm³ at 23 weeks' GA

fig 7.

Relationship between germinal matrix (open circles), lateral ventricles (solid circles), and brain. It is noteworthy that the volumetric ratio of the germinal matrix to brain volume is constant at about 5% between 11 and 23 weeks' GA