Microvascular Alterations and Edema in Focal Cerebral Ischemia

Summary

The sequential morphologic changes in ischemic cerebral edema were studied in squirrel monkeys following middle cerebral artery occlusion. The edema appeared to develop in a diphasic fashion. The primary phase was characterized by astrocytic swelling which spread in an orderly centrifugal fashion beginning in the vicinity of capillaries. Enlargement of the extracellular space of both gray and white matter was noted. This phase began shortly following vessel occlusion and increased gradually in severity with only slight swelling grossly evident. The secondary phase was characterized by tissue necrosis, rupture of cell membranes, and massive accumulation of fluid. This phase began approximately 6 h following vessel occlusion and increased rapidly in severity. Progressive reduction of capillary luminal dimensions was demonstrated. A significant reduction in mean capillary diameter was noted as early as 90 min. Complete obstruction to the passage of erythrocytes was evident by 6 h. Narrowing of capillaries was thought to be the result of compression, initially by swollen pericapillary astrocytic processes and later by increased tissue pressure. Endothelial swelling also appeared to be an important factor. The progressive reduction of capillary luminal dimensions was thought to have an important adverse effect on tissue perfusion.