Aortic aneurysms and dissections: Clinical

An aneurysm is a full-thickness dilation of a segment of a blood vessel so that it’s 50 percent greater than its normal diameter, and it’s usually caused by a weakness in the blood vessel wall.

True aneurysms involve all three layers of the arterial wall - the tunica intima, which has endothelial cells; the tunica media, which has smooth muscle; and the tunica adventitia, which has connective tissue as well as vasa vasorum which are the vessels nourishing the aortic wall itself.

There are two major types of aneurysms: fusiform aneurysms, which are uniform in shape with symmetrical dilatation and involves the entire circumference of the aortic wall; and saccular aneurysms, which are localized outpouchings of only a portion of the aortic wall.

Aortic aneurysms are classified by their location along the aorta. Abdominal aortic aneurysms involve the segment of the aorta within the abdominal cavity. Thoracic aortic aneurysms are found within the chest; and these are further classified as ascending or descending aneurysms. Finally, there’s thoracoabdominal aortic aneurysms, which involve both the thoracic and abdominal aorta.

AAAs are the most common form of aneurysm, usually involving the infrarenal segment of the aorta, inferior to the renal arteries and superior to the iliac bifurcation. An AAA is defined as dilation with a transverse diameter exceeding 3 centimeters.

Most individuals with abdominal aortic aneurysm, or AAA, have no symptoms and are only detected as an incidental finding on imaging studies performed to evaluate an unrelated condition. Some cases, especially in thinner individuals, may be discovered on a routine physical examination as a pulsating abdominal mass that can be felt on palpation and heard as a bruit on auscultation.