Overview of Aortic Aneurysms
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.