Dissecting Aneurysm of the Aorta
ARTHUR L. SCHERBEL, M.D.
Division of Medicine
JOHN B. HAZARD, M.D.
Department of Pathology
VICTOR G. DEWOLFE, M.D.
Department of Cardiovascular Disease
DISSECTING ANEURYSM OF THE AORTA is an intramural separation of the aortic wall by circulating blood that has penetrated and extended into the media. The process may arrest at this stage and heal, progress immediately, or extend at some later date. As the dissecting aneurysm progresses, it may rupture through the adventitia into the pericardial, pleural, or abdominal cavities and may obstruct arteries arising from the aorta. It may rupture back into the lumen and form a double-barreled aorta, which may persist, or the aneurysm may be filled with clot and subsequently heal, obliterating the secondary channel.
Although the specific cause of the disease is not known, the lesion that generally is accepted as being precedent to dissecting aneurysm of the aorta is medial degeneration. This most often consists of mucoid changes in the media and focal loss of elastic tissue (Fig. 1); degeneration of muscle also may occur. The intimal rupture, almost universally present, may vary in size from a small defect a few millimeters in diameter to a large and nearly circumferential laceration. Some believe that the initial lesion may be hemorrhage into degenerated media derived from rupture of vasa vasorum. The originating point (Fig. 2) of dissection is predominantly in the ascending aorta, within a few centimeters of the aortic valve. It may occur in the regions of the ligamentum arteriosum and the left subclavian artery. The intramural dissection (Fig. 3) is of variable length and occurs mostly in the outer third of the media (Fig.. . .