Early events in the formation of a venous thrombus following local trauma and stasis.

A jugular vein was exposed in 20 cats divided into four groups of five cats each. In group 1 the vein was removed immediately after exposure. In group 2 the vein was removed after three 5-minute periods of stasis and reflow. Groups 3 and 4 had the jugular vein occluded for 24 and 72 hours, respectively. In all groups, veins were perfused under physiologic pressure by heparinized saline to remove blood and immersed in 2.5% glutaraldehyde for fixation. All vessels were prepared for scanning and transmission electron microscopy. Group 1 cats had a normal-appearing luminal surface. Group 2 cats had deposition of leukocytes with few erythrocytes or platelets. Groups 3 and 4 had deposition of leukocytes, platelets, and erythrocytes. Leukocytes were found in all areas and associated with all cell types. Platelets and erythrocytes were seldom found in the absence of leukocytes. Thrombi were found on normal-appearing and damaged endothelium. The majority of thrombi were found at side branches and valve pockets. Our results suggest that leukocytes play a primary role in the initiation of deep vein thrombosis. Platelets may have only a secondary role.