Development of Cerebellar Connectivity in Human Fetal Brains Revealed by High Angular Resolution Diffusion Tractography

摘要

High angular resolution diffusion imaging (HARDI) tractography has provided insight into major white matter pathways and cortical development in the human fetal cerebrum. Our objective in this study was to further apply HARDI tracography to the developing human cerebellum ranging in fetal and adult stages, to outline in broad strokes the 3-dimensional development of white matter and local gray matter organization in the cerebellum. We imaged intact fixed fetal cerebellum specimens at 17 gestational weeks (W), 21W, 31W, 36W, and 38W along with an adult cerebellum for comparison. At the studied earliest gestational age (17W), coherent pathways that formed the superior, middle, inferior cerebellar peduncles were already detected, but pathways between deep cerebellar nuclei and the cortex were not observed until after 38W. At 36–38W, we identified emerging regional specification of the middle cerebellar peduncle. In the cerebellar cortex, we observed disappearance of radial organization in the sagittal orientation during the studied developmental stages similar to our previous observations in developing cerebral cortex. In contrast, in the axial orientation, cerebellar cortical pathways emerged first sparsely (31W) and then with increased prominence at 36–38W with pathways detected both in the radial and tangential directions to the cortical surface. The cerebellar vermis first contained only tangential pathways to the long axes of folia (17–21W), but pathways parallel to the long axes of folia emerged between 21–31W. Our results show the potential for tractography to image developing cerebellar connectivity using HARDI tractography.