Morphological Study of the Ventriculus Terminalis in the Human Fetal Spinal Cord

Kang, Ho Suck; Song, Dae Yong; Yang, Young Chul; Kim, Ji Won; Cho, Byung Pil

Abstract

The ventriculus terminalis, also known as the 'fifth ventricle', is a dilated cavity in the conus medullaris. It is formed by degenerative process in the course of neural tube development, but the definite function is unclear. And the reports, which have studied the morphological variation according to fetal age, are insufficient. So, in this report, we observed the morphological variation of the ventriculus terminalis and measured the areal ratio of the ventriculus terminalis to the parenchyma of conus medullaris by fetal age. We also studied the fine structure of the conus medullaris and ependyma by electron microscope. The ventriculus terminalis began at the level at which the ependymal cells proliferated and the central canal moved to the dorsal region. Periependymal islet was observed at this level. At the lower level, it immediately extended both lateral sides and finally switched over to the filum terminale. The area ratio of the ventriculus terminalis to the parenchyma of the conus medullaris increased from above downward. Especially, It increased steeply between the Leaf-shaped region and the transitional zone, where the ventriculus terminalis began. But the increasing pattern was too irregular to generalize its pattern by fetal age. The ependyma lining the ventriculus terminalis was composed of pseudostratified ciliated columnar epithelium layer about 5~7 cells thick. It had conspicuous intercellular junctional complexes close to the lumen into which microvilli and cilia projected. At the junction where the ependyma meets the parenchyma of the conus medullaris, we could observe many myelin-like structures made by basolateral membrane of the ependymal cell. In the conus medullaris, we could observe many obscure cell types because they were in the course of differentiation. On the other hand, we could also observe the fully differentiated nerve cells, astrocytes and oligodendrocytes which seemed to play its own role. A lot of developing myelin sheaths were observed and the majority was the degenerative one. Some ependymal cells showed the apoptotic characteristics and many cell debris were observed in the lumen. As a result, the ventriculus terminalis was formed by the combination of cell differentiation and degeneration, and its development was independent of the spinal cord.