[The morphological study of cerebrospinal fluid drainage at monkey arachnoid granulations]

It is generally accepted that the arachnoid granulations play an essential role in the drainage of the cerebrospinal fluid (CSF) into venous system, but there is continuing in controversy as to the morphological features of their functions. The present study was undertaken to investigate the structure and function of monkey arachnoid granulations under the increased pressure of subarachnoid space by light, scanning (SEM) and transmission (TEM) electron microscopy. Granulations were classified into three types by surface endothelial morphology. They were, 1) a granulation covered with bulged endothelium only, 2) a granulation covered with flatten endothelium only, and 3) a granulation covered with both two previous mentioned endothelia. Type 1) and 2) were spherical or hemispherical in shape. Type 3) granulations were lobulated, having the flatten endothelium at the constricted portion and the bulged endothelium in the other major portion. Three kinds of mechanisms for CSF drainage at arachnoid granulations ("closed system", "open system" and "temporary vacuolar transcellular channel") were proved to exist concurrently, because morphological criteria findings of each mechanism were observed in the same specimen. So, we proposed that these arachnoid granulations should be called "arachnoid granulations complexs".