Pathophysiology of Ascending Aortic Aneurysm and Dissection

Abstract

Type A aortic dissection is a highly lethal event that is often but not always associated with ascending aortic aneurysms. The pathophysiology of ascending aneurysms and dissection differs markedly from that of aneurysms and rupture in other areas of the aorta. The ascending aorta is much less likely to be affected by degenerative changes associated with atherosclerosis and inflammation and more likely to be affected by genetic abnormalities that promote patchy dissolution of medial elastic fibers, apoptosis of smooth muscle cells, and rupture or dissection starting in histologically normal-appearing areas. The development of type A dissections and ascending aneurysms is discussed in relation to biomechanics of the ascending aorta, developmental biology, micromechanics of aortic composite structure, microscopic and ultrastructural features of dissections and aneurysms, and biomechanics of pathologic ascending aortas. Ten postulates are offered describing pathophysiologic features of aneurysms and dissections. Dissection is a disease of collagen fibers. Aneurysms are a disease of elastic fibers. Both are strongly associated with hypertension.