Electron Microscopy of Human Arachnoid Villi Removed During Operation in Different Pathological Conditions
The functional morphology of arachnoid villi has been studied by electron microscopy in different animals and in various experimental conditions (Potts and Gomez 1975). The processes of CSF reabsorption through the arachnoid granulations to the venous system were correlated to the ultrastructural aspects of the villi, that show variable results in the different species and depend on the pressure gradient between CSF and the venous lumen (Gomez et al. 1974). A study of the functional ultrastructure of human arachnoid villi obtained by surgical biopsies has been previously reported by our research group (D’Avella et al. 1980). The villi were removed from patients considered in “physiological” conditions because of normal ICP and CSF pressure gradient. The ultrastructure of the villi provided evidence for both closed and open systems for CSF reabsorption: micropinocytotic vesicles and giant vacuoles in the endothelial cells covering the villi are consistent with an active process of CSF transport across the cytoplasm, while the gaps between adjacent endothelial cells and the endothelium-lined open channels permit a bulk flow of the CSF in the venous lumen (D’Avella et al. 1980). These data support the concept of two different and additional mechanisms for CSF reabsorption, regulated by a high and a low pressure systems (Lorenzo et al. 1970). Failure of either pressure-dependent absorption system may probably occur in different pathological conditions, but ultrastructural examination of human pathological cases for correlative studies is obviously very difficult. Biopsies of arachnoid granulations removed from dural veins accidentally interrupted during operation are only rarely obtained. In the last two years we were able to study by electron microscopy (T.E.M.) three cases in which the villi can be considered drawn and fixed in “pathological” conditions, both for clinical and ICP factors.
KeywordsNormal Pressure Hydrocephalus Arachnoid Granulation Arachnoid Villus Arachnoidal Cell Ultrastructural Aspect
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