Aneurysms are abnormal dilations of arteries caused by weakening of the arterial wall. Common causes include hypertension, atherosclerosis, infection, trauma, and hereditary or acquired connective tissue disorders (eg, Marfan syndrome, Ehlers-Danlos syndrome). Aneurysms are usually asymptomatic but can cause pain and lead to ischemia, thromboembolism, spontaneous dissection, and rupture, which may be fatal. Diagnosis is by imaging tests (eg, ultrasonography, CT angiography, magnetic resonance angiography, aortography). Unruptured aneurysms may be treated with medical management or surgical intervention depending on symptoms and the size and location of the aneurysm. Medical management includes risk factor modification (eg, strict BP control) plus scheduled surveillance imaging. Surgical intervention includes open repair or endovascular stent-graft surgery. Treatment of ruptured aneurysms is immediate repair with either an open surgical synthetic graft or an endovascular stent graft.

The aorta originates at the left ventricle above the aortic valve, travels upward (ascending thoracic aorta) to the first branch of the aorta (brachiocephalic or innominate artery), arches up and behind the heart (aortic arch), then turns downward distal to the left subclavian artery (descending aorta) through the thorax (thoracic aorta) and abdomen (abdominal aorta). The abdominal aorta ends by dividing into the right and left common iliac arteries.

The wall of the aorta is composed of three layers:

Aneurysms are abnormal dilations of arteries defined as a ≥ 50% increase in arterial diameter compared with normal segments. They are caused by weakening of the arterial wall, specifically, the media. True aneurysms involve all 3 layers of the artery (intima, media, and adventitia). Aneurysmal disease is not a focal problem and can extend along the aorta with time.

A pseudoaneurysm (false aneurysm) is a communication between the arterial lumen and overlying connective tissue resulting from arterial rupture; a blood-filled cavity forms outside the vessel wall and seals the leak as it thromboses.

Aneurysms are classified as

Layered (laminated) thrombus may line the walls of either type as the result of alterations in flow within the aneurysmal segment.

Aneurysms may occur in any artery. The most common and significant are

Aneurysms of the major aortic branches (subclavian and splanchnic arteries) are much less common. Aneurysms of peripheral arteries and the cerebrovascular system (causing stroke) are discussed elsewhere.