Updated: September 19, 2006
Causes and risk factors
- Age over 55 years (Risk increases with age)
- A family history of AAA is particularly concerning
- High blood pressure
Most aneurysms are caused by a breakdown in the proteins that provide the structural strength to the wall of the aorta. These proteins, called collagen and elastin can gradually deteriorate with age, but inflammation that is associated with atherosclerosis can accelerate this process even in younger people. There are also naturally occurring enzymes that cause the breakdown of collagen and elastin. An excess of these enzymes or other conditions that activate these enzymes may also contribute to the formation of an aneurysm, or its sudden growth. In rare cases an aneurysm may be caused by infection (mycotic aneurysms). There is still much to be learned about the cause of aneurysms and their growth, but fortunately we have successful, permanent treatments for AAA when they occur. Vascular surgeons have performed much of the basic research on aneurysm formation.
Types of Aortic Aneurysms
Aortic aneurysms are classified by shape, location along the aorta, and how they are formed.
True aneurysms and pseudoaneurysms
The wall of the aorta is made up of three layers: a thin inner layer of smooth cells called the endothelium, a muscular middle layer which has elastic fibers in it called the media, and a tough outer layer called the adventitia. When the walls of the aneurysm have all three layers, they are called true aneurysms. If the wall of the aneurysm has only the outer layer remaining, it is called a pseudoaneurysm. Pseudoaneurysms may occur as a result of trauma when the inner layers are torn apart.
- Fusiform aneurysms
Most fusiform aneurysms are true aneurysms. The weakness is often along an extended section of the aorta and involves the entire circumference of the aorta. The weakened portion appears as a generally symmetrical bulge.
- Saccular aneurysms
Occasionally an aneurysm may occur because of a localized weakness of the artery wall (saccular). Saccular aneurysms appear like a small blister or bleb on the side of the aorta and are asymmetrical. Typically they are pseudoaneurysms caused either by trauma (such as a car accident) or as the result of a penetrating aortic ulcer.
- Thoracic aortic aneurysm (TAA)
A TAA is a diseased, weakened, and bulging section of the aorta in the chest. This condition, if not treated, could result in a rupture of the aorta, leading to life-threatening internal bleeding. The aneurysm may be caused by vascular disease, injury, or a genetic defect of the tissue. TAA is sometimes found in people with Marfan?s syndrome, which is characterized by many anomalies including elongated bones. It is also associated with Turner syndrome, which results from a missing X chromosome and is associated with dwarfism and arrested sexual development in addition to aortic aneurysm. TAA also can run in families independent of those two syndromes. Because it is difficult to diagnose victims often die young. People with TAA remain unaware of the risk they face because the slowly enlarging aorta does not cause any symptoms until it has reached a critical diameter. At that point, the aorta dissects or ruptures, both of which are life-threatening. Typically, the patient develops chest pain and usually goes to an emergency department to seek treatment.
- Abdominal aortic aneurysm (AAA)
More than 90% of abdominal aortic aneurysms originate below the renal arteries. The diameter is the most important predictor of aneurysm rupture with up to a 40% risk of rupture over 5 years for aneurysm > 5 cm. When they do rupture they tend to rupture leftward and posteriorly.
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