Development of the Cerebrospinal Fluid Pathway in the Normal and Abnormal Human Embryos

Abstract

The subarachnoid space, the chorioid plexus and the arachnoid villi are microscopically studied in 60 normal human embryos and in 3 abnormal human embryos with rhombencephaloschisis and cervical myeloschisis. The subarachnoid space has been generally considered to be developed by outflow of cerebrospinal fluid (CSF) of the choroid-plexus origin from the IVth ventricle. This generally accepted concept does not meet with our findings: (1) cavity formation in the meninx primitiva is seen before appearance of the choroid plexus; (2) the primitive subarachnoid space is developed earlier in the prepontine region than in the area dorsal to the rhombic roof, and (3) the primitive subarachnoid space is formed in the embryos with dysraphism where the perineural subarachnoid space is separated from the ventricles. Apparently the embryonic pattern of CSF circulation should be much different from the generally believed pattern of adult, since the arachnoid villi are absent in the embryos and the ability of production of CSF in the embryonic choroid plexus is questionable. It is suggested that such embryonic pattern of CSF production and absorption may partly persist in adult human being.

Interhemispheric Osteolipoma with Agenesis of the Corpus Callosum

“…The inner meninx is normally resorbed in an orderly process, as the subarachnoid cisterns expand into the space around it 15,18) . Truwit and Barkovich 18) described the preferential cisternal sites of intracranial lipomas, based on the orderly formation of the cisterns proposed by Osaka et al 15) They reported that since the meninx primitiva dissolves last in the region dorsal to the lamina terminalis, the chance that the meninx will differentiate abnormally is greatest in the interhemispheric area, which makes it the most common site for intracranial lipomas to occur. If the meninx primitiva regresses incompletely, adjacent neural structures may fail to develop or would develop improperly to form lipomas.…”

Visualization of the cerebrospinal fluid drainage into the Galen's vein.

“…The former appears early in development phylogenetically and ontogenetically (OSAKA et al, 1980), whereas the latter appear later and increase in number and size in accordance with the increasing cranial volume and aging. They are more suitably regarded as a tool to prevent the central nervous tissue from compression caused by a sudden rise of the intracranial pressure.…”

“…This view has been applied even to lower mammals (MANN et al, 1979), although the arachnoid granulations appear later than does the CSF, both ontogenetically and phylogenetically (OSAKA et al, 1980). This discrepancy has not yet been explained satisfactorily even though BUTLER et al (1983) recently showed some transcellular channels in the sinus endothelium covering "arachnoid villi within dural wall" in the rat.…”

The Embryological Development of the Form of the Trabeculae Bridging the Subaracnoid Space

“…Gases move through this gel by diffusion, there is no bulk movement. Osaka et al refer to this stage as meninx primitivea, or primitive subarachnoid space [10]. Initially there are no Pial or Arachnoid membranes in the PPAS.…”

“…These remaining walls are the trabeculae. Osaka described the resultant fluid space as "essentially the 'cleared-out connective tissue space' which is formed in late embryonic life" [10].…”