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Abdominal Aortic Aneurysm (AAA)

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Updated November 13, 2011

If you have been told you have an abdominal aortic aneurysm (AAA), it means that a localized section of your aorta within your abdomen has developed a balloon-like dilation known as an aneurysm. The main problem caused by AAA is the rupture of the aneurysm, an event which is often catastrophic.

This means that it will be important for you and your doctor to decide whether your AAA poses a sufficient risk of rupture that it ought to be treated now, or whether it can be safely monitored over time. This article will help you learn what you need to know about AAA so you can make the decision that is right for you.

What Are the Symptoms of AAA?

Most people with AAA have no symptoms unless the aneurysm ruptures. Occasionally, AAA can produce abdominal or back pain, or a tender spot in the abdomen. These symptoms - which, again, are uncommon - may indicate that a recent expansion of the aneurysm has occurred, and may be a sign that a rupture is likely to happen. Most ruptures, however, occur without any prior symptoms whatsoever.

Rupture of an AAA usually causes massive internal bleeding within the abdomen, and is often quickly fatal. Patients who survive long enough to get to an emergency room usually have severe abdominal or back pain, and a dangerously low blood pressure. Only about 25% of patients who suffer a ruptured AAA will survive. In fact, AAA is an important cause of unexplained sudden death in older people.

What Causes AAA?

Surprisingly, the cause of AAA is still largely unknown. While atherosclerosis is often present in patients with AAA, experts do not agree whether atherosclerosis actually causes the aneurysm. It is now felt that in many if not most cases, AAA is caused by genetic factors that lead to defects in some of the proteins within the wall of the aorta, and which make the blood vessel prone to dilation.

AAA occurs much more commonly in men than in women, and is rare in people under 60 years of age. A family history of AAA is an important risk factor. Hypertension is another risk factor for AAA. But smoking, by far, is the major risk factor for AAA. Smokers have a 5-fold increase in the incidence of AAA compared with non-smokers.

How is AAA Diagnosed?

Because the initial symptoms of AAA are most often due to rupture, and because rupture is most often fatal, ideally AAA should be diagnosed before it produces any symptoms.

It is usually difficult to diagnose AAA by physical examination (only 30% of AAA are initially detected in this way), so most pre-rupture AAAs are diagnosed when patients who are judged to be at increased risk for AAA are specifically screened for it, usually with an ultrasound (echo) study.

Which individuals should be screened for AAA, and when to screen them, turns out to be a controversial question. Learn more about whether you should be screened for AAA.

Who Should Be Treated For AAA?

If you have been told you have an AAA, you and your doctor will have to decide whether you should have surgical repair of the aneurysm to prevent rupture, or instead whether your AAA should be carefully monitored over time. To a large extent, this decision will depend on the estimated likelihood that your AAA will rupture, and on your estimated risk from surgery.

Many patients with AAA have other cardiovascular disorders (due to their age and risk factors), so the risk of surgical AAA repair will not be trivial. In general, the risk of dying from the surgical procedure is usually about 5% or less, but the risk of surgery in your own case will depend on your individual situation, which will need to be carefully assessed by your doctor.

The likelihood that an AAA will rupture appears to depend largely on two factors: the size of the AAA, and the rate of growth of the AAA.

The size of the AAA is usually the best indicator of the risk of rupture. The size of an AAA can be measured by ultrasound testing, CT scan, or MRI. Aneurysms greater than 5.5 cm in diameter in men, or greater than 5.0 cm in women, are dramatically more likely to rupture than smaller aneurysms. If these "threshold" diameter values have been reached, the risk of rupture is greater than 40% over five years, and surgery is often recommended. Below these threshold values, the risk of rupture is usually similar to the risk of complications from surgery, so surgery is often not recommended.

If surgery is not recommended, then regular reassessments of the size of the AAA should be made. If the AAA grows in size by more than 0.5 cm in a year, the risk of rupture is much higher - and surgery is usually recommended even if the overall size of the AAA is still less than 5.0 or 5.5 cm.

How is AAA Treated?

The treatment of AAA is usually surgical. Learn more about the treatment of AAA.

Summary

Having an AAA usually presents you with a difficult choice. AAA generally causes no difficulties whatsoever until it produces a sudden medical catastrophe, so you are faced with having to choose when - and whether - to have a relatively big surgical procedure to prevent such a catastrophe. This choice is often only made more difficult by the fact that you may be feeling just fine right now.

The right decision for you will depend on your own medical condition, the size and the rate of growth of your AAA, and a careful balancing of your overall individual risks in taking action now versus watchful waiting. So making the best decision will require close cooperation and excellent communication between you and your doctor.

Sources:

Nevitt, MP, Ballard, DJ, Hallett, JW Jr. Prognosis of abdominal aortic aneurysms. A population-based study. N Engl J Med 1989; 321:1009.

Creager, MA, Halperin, JL, Whittemore, AD. Aneurysmal disease of the aorta and its branches. In: Vascular Medicine, Loscalzo, J, Creager, MA, Dzau, VJ (Ed), Little, Brown, New York, 1996, p. 901.

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