[Light and electron microscopic studies on the subdural space, the subarachnoid space and the arachnoid membrane].

Cranial meninges of humans were studied by electron microscopy after fixation in situ and histochemical demonstration of nicotinamide-adenine dinucleotide diaphorase within mitochon dria. There was an intimate fusion between the innermost portion of the dura mater (dural border cells) and the outermost portion of the arachnoid (arachnoid barrier layer). Cranial meninges did not contain a true subdural space, when specimens were well prepared with spatial relationships preserved. If cleavage had occurred during preparation, the subdural space was artificially formed by the separation of dural border cells, because the latter showed a paucity of intercellular contacts and weak collagenous reinforcements. The arachnoid barrier layer was a squamous layer of elongated cells with numerous tonofilaments, desmosomes and tight junctions. There was a lining of junctional devices between the innermost two cell layers. There was a number of extracellular lacunae, being separated by inter digitations and containing collagen fibrils, elastins, granular material and matrix vesicles with or without psammoma bodies. The mitochondrial enzymes of this layer showed negative activity in intact specimens, but a positive one in cleaved dural border cells and arachnoid trabecular cells. An incomplete basement membrane covered the innermost aspect of this layer. The arachnoid trabecular cells generally had electron-lucent cytoplasm with a few tonofilaments. The cells beneath the arachnoid barrier layer had oval nuclei and wide cytoplasm containing numerous mitochondria. This layer was anchored by flattened or button-shaped pedicles, otherwise these cells formed an epithelial cluster. The cells lying within the subarachnoid space had elongated nuclei and cytoplasmic projections. The arachnoid trabeculae consisted of both a network of arachnoid trabecular cells and interwoven collagen fibrils. Alternating with these cells were numerous resting macrophages.