The Cranial Arachnoid and Pia Mater in Man: Anatomical and Ultrastructural Observations

Abstract

The objects of the present study were: (1) to define the relationships of the arachnoid mater to blood vessels in the subarachnoid space; (2) to establish the structure of leptomeningeal trabeculae and their relationships to the pia mater; and (3) to investigate the fine structure of the human pia mater. Intracranial portions of vertebral artery were taken at post mortem, and normal cerebral cortex and overlying leptomeninges were obtained from surgical lobectomies. Tissue from these specimens was examined by scanning and transmission electron microscopy, by light microscopy and by immunocytochemistry for the presence of basement membrane, desmosomal proteins and vimentin. Results of the study showed that as the vertebral artery pierced the posterior atlanto-occipital membrane and entered the subarachnoid space, it acquired a leptomeningeal coat as the arachnoid was reflected on to it. It has been demonstrated previously that as vessels enter the brain, the leptomeningeal coat is reflected on to the surface of the cortex as the pia mater. The arachnoid mater was seen to consist of a subdural mesothelial layer and a compact central layer as previously reported. From the inner layer of the arachnoid, collagen bundles coated by leptomeningeal cells extended as trabeculae across the subarachnoid space to fuse with the pia mater. The pia itself was composed of a delicate but apparently continuous layer of cells joined by desmosomes and gap junctions but no tight junctions were observed. It was possible to detect pia mater cells in the perivascular spaces of the brain by immunocytochemical techniques using light microscopy. The significance of the observed anatomical arrangement for cerebrospinal fluid physiology is discussed.

The role of brain barriers in fluid movement in the CNS: is there a ‘glymphatic’ system?

“…Studies of nose-to-brain transport further support some degree of separation between CSF and ISF [181]. Földi and colleagues have long proposed that drainage of ISF along the PVS is indeed compartmentalized from the CSF as it drains from the brain, possibly by the presence of the cells ensheathing the vessel in the subarachnoid space [61] (e.g., as described by [4]). In addition to tracer studies, antigenic responses also appear to suggest a compartmentation of CSF and ISF [58,66], as parenchymal tissue grafts and ISF antigens elicit more limited immune responses (e.g., [122,155,167]) than CSF-administered tissue or antigen that usually results in a strong immune response (e.g., [122,167]).…”

Differential Gene Expression during Meningeal-Meningococcal Interaction: Evidence for Self-Defense and Early Release of Cytokines and Chemokines

“…The leptomeninges surrounding the subarachnoid space consist of the arachnoid mater and the pia mater, separated by trabeculae and lined by a type of epithelium termed meningothelial cells (1). The basic cell type and fine structure of these layers have many similarities.…”

Comparison of the Inflammatory Responses of Human Meningeal Cells following Challenge withNeisseria lactamicaand withNeisseria meningitidis

“…In humans, the meninges comprise the pachymenix (dura mater) and the leptomeninges, which consists of the arachnoid and pia mater together with the trabeculae that traverse the cerebrospinal fluid (CSF)-filled subarachnoid space (SAS) (4,25). The bacterial etiology of meningitis is broad, and susceptibility to the causative organisms varies with age, with different groups of organisms affecting neonates, children, and adults (28).…”