Transintimal clefts or "channels" of normal and atherosclerotic coronary arteries (a preliminary study)

Transintimal clefts or "channels" have been found in the coronary arteries of children, adolescents, young and mature adults up to 40 years old; they appeared on light microscope examination as sinusoid-like spaces running from the endothelium to the internal elastic membrane. The mean luminal diameter was 5-6 micrometers, and the maximum density per mm2 varied between 15 (anterior descending artery) and 3 (left main coronary artery). Transintimal clefts or "channels" developed as cylindrical tunnels into the intimal connective tissue surrounded by a coat of ground substance rich in heparan sulfate; blood red cells, leucocytes and platelets were not present in their lumen. In serial cross-sections and camera lucida drawings transintimal "channels" appeared as blind tubes ending either in the inner or outer half of the thickened intima or at the intima-media frontier. We were unable to reveal connections with media vasa vasorum. Atherosclerotic plaques undergoing a mucoid transformation or submitted to swelling and/or dissecting necrosis occurred constantly connected with the coronary artery lumen by transintimal "channels". Many light microscopic pictures suggested that the necrotizing agent(s) of plasma spreads along the course of transintimal "channels" and reached the basal intimal regions or the basal areas of developing and preexisting atherosclerotic plaques. The implications of the presence of transintimal clefts or "channels" in the pathogenesis of human atherosclerosis are discussed.