Electron microscopic observations of endothelial junctions in perifocal human brain edema. An interpretative study.

Cortical biopsies of 12 patients with diagnosis of cerebral tumor or complicated brain trauma were studied with the electron microscope to analyse the alterations of endothelial junctions and their probable participation in the pathogenesis of human brain edema. Capillaries with increased vesicular and vacuolar transport from areas with moderate and severe edema were examined. Some endothelial tight junctions were structurally closed and intact while others showed openings and dehiscence of processes. Some accessory mechanisms of bypassing the endothelial junctions were found, such as: a) communicating micropinocytotic vesicles with the extracellular space at the basal segment of endothelial junction; b) chained micropinocytotic vesicles between endothelial luminal membrane and basal segment of endothelial junction and c) tubular structures connecting the extracellular pockets of endothelial junction with the basement membrane bifurcation. In severe brain edema a considerable enlargement of interjunctional pockets of extracellular space was seen, suggesting that in highly increased cerebrovascular permeability the endothelial junctions are partially opened and that an intercellular route through interendothelial clefts for transferring hematogenous edema fluid from blood to the capillary basement membrane is formed.