An aortic aneurysm is the dilation, bulging or ballooning out of part of the wall of the aorta. Typically, the widening of such an area is considered to be an aneurysm when it is more than 1.5 times its normal size. The pressure of blood flow within the aorta, particularly if the walls have been weakened and damaged by plaque buildup, may eventually lead to the aneurysm expanding and rupturing. Ruptures are very painful events that causes massive internal bleeding. The patient usually must be treated within minutes to hours in order to have a chance of survival. The survival rate of those with ruptured aortic aneurysms is less than 50 percent.

Aortic aneurysms may be classified a number of ways. They are often grouped by where they occur along the length of the aorta, or by the form of the aneurysm itself. Forms of aneurysm include:

Aneurysms are also commonly grouped by where they occur along the length of the aorta. If they occur in the ascending aorta, aortic arch or the portion of the aorta that travels through the upper chest (descending thoracic aorta), they are known as thoracic aortic aneurysms. These account for about 25 percent of aortic aneurysms. If they occur in the portion of the aorta that runs through the abdomen, down toward the branch of the iliac arteries, they are known as abdominal aortic aneurysms. They account for about 75 percent of aortic aneurysms.

The underlying causes of aortic aneurysms are somewhat related to their location. Thoracic aortic aneurysms are connected to atherosclerosis (“hardening of the arteries”), inherited disorders such as Marfan syndrome or Ehlers-Danlos syndrome or high blood pressure. Because of their proximity to the heart, thoracic aortic aneurysms may cause heart attack by pressing on the coronary arteries or heart failure by causing the aortic valve to function abnormally. Most patients with thoracic aortic aneurysms also have other forms of heart disease, and as many as 25 percent also have abdominal aortic aneurysms.

Abdominal aortic aneurysms are about three times as common as thoracic aortic aneurysms. They usually occur in patients over the age of 50, and they become more common as people age. They are also much more common (about four to five times) in men as women. The causes of abdominal aortic aneurysms are not completely understood, but they are more common in patients with atherosclerosis and high blood pressure, and inflammation as measured by C-reactive protein, seems to play a role in the process. They also appear to run in families. More than one quarter of patients diagnosed with such an aneurysm have a close relative with the same condition.

Aneurysms in the arteries of the heart can also develop from cocaine use. Researchers feel that a person’s risk increases with the amount of cocaine used, and that this risk is irreversible. Both kinds of aneurysms are also affected by smoking. Cigarette smoking has been shown to cause aneurysms to grow larger and more rapidly, thus increasing their risk of rupture. Quitting smoking is a major element of non-surgical therapy for aneurysm.