INTIMAL HYPERPLASIA PRODUCING THROMBUS ORGANIZATION IN AN EXPERIMENTAL VENOUS THROMBOSIS MODEL

Purpose: A venous thrombosis animal model demonstrated similarities be tween intimal hyperplasia and thrombus organization. This has prompted the evaluation of a hypothesis that intimal hyperplasia may be the me chanism for thrombus organization in veins with normal pressure. Metho ds: Thrombi were produced in surgically exposed jugular veins of anest hetized, 18 to 20 kg pigs. Thrombosis was induced by a combination of devascularization, electric injury produced by a low amperage, direct current, and permanent partial ligation (50% diameter reduction). Vein segments were harvested at 0, 1, 2, 7, 14, and 60 days and histologic ally examined for fibrin, red blood cells, platelets, smooth muscle ce lls, endothelial cells, elastic fibers, and collagen deposits. Results : Forty vein segments in 20 pigs were evaluated. Luminal thrombi with thickened walls developed in all specimens. All luminal thrombi demons trated partial spontaneous thrombolysis over the period of observation . Intimal thickening consisting primarily of smooth muscle cells by da y 2 was apparent and progressed until about 2 weeks, when collagen dep osits became prominent within the neointima. The neointima frequently comprised half the cross-sectional area of the veins. Endothelial cell s were present in the intima as single cells or as lining for clefts f ormed within the thickened intima. Conclusions: Smooth muscle cell pro liferation with collagen deposition characteristic of intimal hyperpla sia seemed to be the mechanism of thrombus organization in the experim ental thrombosis model used in this study in which extensive stimulati on was used to produce thrombosis.