Introduction to Abdominal Aortic Aneurysm

Natural Progression of Abdominal Aortic Aneurysm

The natural history of abdominal aortic aneurysms (AAA) is difficult to determine and predict on an individual basis despite increasing knowledge and information in recent years about aneurysm growth patterns. Different patterns of expansion have been noted in patients with abdominal aortic aneurysm who have been followed by serial non-invasive methods, such as abdominal ultrasound. Some aneurysms may remain stable for long periods while others enlarge progressively or expand rapidly. The average expansion rate has been estimated to be about a 10% increase in diameter per year.

An abdominal aortic aneurysm may develop slowly over many years without producing any readily apparent clinical symptoms. In fact, about 60% to 70% of patients with abdominal aortic aneurysm are asymptomatic. Small AAAs present a very low risk for rupture but they must be followed carefully to monitor their expansion in order to minimize the risk of rupture. Screening studies involving ultrasound imaging indicate that approximately 5% of men above the age of 65 have small abdominal aortic aneurysms ranging in size from 3-6 cm. When the aneurysm reaches a diameter of 5.5 cm. elective surgical repair of the aneurysm is recommended as it significantly reduces the rate of rupture and mortality.

There is continuing debate regarding the threshold diameters used to determine the appropriate time for elective surgical intervention. There are indications that some people may require intervention before the aneurysm reaches 5.5 cm and others may be able to wait until it is slightly larger. Surgeons therefore take into account that the cutoff diameter for surgery is just an average and may vary for each person depending upon:

• Gender - women may require a lower standard of diameter size before intervention. The Joint Council of the American Association for Vascular Surgery (JCAAVS) recommends that the threshold for intervention for women be considered at 5.0 cm.

• Body habitus - obese individuals may be able to reach a higher diameter before intervention

• Family history of abdominal aortic aneurysm

Many abdominal aortic aneurysms remain small, however, they may expand and may do so at different rates. When expansion is present, the aneurysm is followed very carefully for size and rate of expansion since each determines the point at which surgical intervention is considered - i.e. if the size reaches 5.5 cm. (average) or if expansion rate is greater than 1 cm. per year.

Although it appears that the risk of rupture is low for aneurysms below 5.0 cm., it is critical for each patient be carefully evaluated on an ongoing basis and that individuals with small AAAs comply fully with the monitoring schedule set forth by their physician.