MEDizzy - During a routine physical examination, a 60-year-old man is

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Cardiovascular System

During a routine physical examination, a 60-year-old man is found to have a 5-cm pulsatile mass in his abdomen. Angiography reveals a marked dilation of his aorta distal to his renal arteries. Which of the following is the most likely cause of this aneurysm?

ExplanationAn aneurysm is an abnormal dilation of any vessel. The causes of aneurysms are many, but the two most important ones are atherosclerosis and cystic medial necrosis. Atherosclerotic aneurysms, the most common type of aortic aneurysms, usually occur distal to the renal arteries and proximal to the bifurcation of the aorta. Many atherosclerotic aneurysms are asymptomatic, but if they rupture they produce sudden, severe abdominal pain, shock, and a risk of death. Prior to rupture, physical examination reveals a pulsatile mass in the abdomen. Cystic medial necrosis refers to the focal loss of elastic and muscle fibers in the media of vessels and is seen in patients with hypertension, dissecting aneurysms, and Marfan syndrome. Trauma may also lead to the formation of dissecting aneurysms. Berry aneurysms, found at the bifurcation of arteries in the circle of Willis, are due to congenital defects in the vascular wall. Syphilitic (luetic) aneurysms are caused by obliterative endarteritis of the vasa vasorum of the aorta. These aneurysms are part of the tertiary manifestation of syphilis and become evident 15 to 20 years after persons have contracted the initial infection with Treponema pallidum. Elastic tissue and smooth-muscle cells of the media undergo ischemic destruction as a result of the treponemal infection (obliterative endarteritis). As a consequence of ischemia in the media, musculoelastic support is lost and fibrosis occurs. Grossly, the aorta has a “tree-bark” appearance. Luetic aneurysms almost always occur in the thoracic aorta and may lead to luetic heart disease by producing insufficiency of the aortic valve (aortic regurgitation).