An 80-year old male diabetic has a 7-cm, pulsating mass in the midline of his lower abdomen, He has poor pulses in his lower extremities. Which of the following complications of aoic atherosclerosis is responsible for the development of this lesion?

Aneurysms, including aoic aneurysms, form in areas of weakness of an aerial wall. Abdominal aoic aneurysms are typically atherosclerotic in origin. Atherosclerotic plaques compress the media, and this can cause atrophy of the media. Because the media provides elasticity and suppo to the vessel wall, weakening of the media predisposes to aneurysmal dilatation. Ulceration, thrombosis, and hemorrhage occur superficially in atheromatous plaques and tend to promote narrowing of aerial lumens, not aerial dilation. Cystic medial necrosis is a feature of Marfan syndrome.