An abdominal aortic aneurysm (AAA) is an expansion of the aorta below the renal arteries to a maximal diameter of 3 cm or greater. The prevalence of AAAs, as detected by screening ultrasonography, is about 4%-9% in men and 1% in women.
Although the condition may be asymptomatic for years, as many as one in three eventually rupture if left untreated. In the US, AAA accounts for an estimated 15,000 deaths annually, with most fatalities occurring in men 65 years of age and older.
While the prognosis is grim for undiagnosed abdominal aortic aneurysm, ultrasound of the abdomen is known to be accurate and reliable (95% sensitivity and 100% specificity) in detecting the condition, and survival after elective surgical repair approaches that of the general population.
Elective AAA repair, however, carries significant risks, such as operative mortality, myocardial infarction, respiratory failure, and renal failure.
In 1996, the US Prevention Services Task Force (USPSTF) found insufficient evidence to recommend either for or against routine abdominal aortic aneurysm ultrasound screening for adults.
The task force, a group of health experts that reviews published research and makes recommendations about preventive health care, cited the need for data from population-based screening trials to determine whether the potential benefits gained from preventing a ruptured AAA justify the potential risks involved with the surgery necessary for its repair.
Since 1994, the results of several such studies have been published, and the results of four of those studies were analyzed by a team of investigators at the Oregon Evidence-based Practice in Portland. In light of their analysis, the USPSTF has revised its recommendations regarding abdominal aortic aneurysm screening. Results of the Oregon researchers' analysis as well as the revised task force recommendations appear in the January 31 issue of Annals of Medicine.
In their study, the Oregon researchers examined the results of four population-based, randomized, controlled trials of abdominal aortic aneurysm screening. Their analysis revealed the following:
- Screened patients had lower rates of dying of a ruptured AAA than did unscreened patients.
- AAA was much more common in men than in women and was most common in male smokers.
- Of all patients dying of AAA rupture, 95% were older than age 65.
- Death from AAA rupture is rare after negative results on ultrasonography at age 65.
- Repair improved outcomes for patients with aneurysms larger than 5.5 cm.
- Screening can cause short-term anxiety, but there is no evidence of long-lasting psychological side effects.
- No significant reduction in AAA-related mortality in women has been associated with screening.
Responding to these findings, USPSTF members recommended the following:
- Men who are current or former smokers should be screened for AAA by ultrasound once between ages 65 and 75.
- Women in general should not undergo ultrasound screening for AAA.
- Ultrasonography to look for AAA is indicated in any patient with abnormal findings on medical examination or with symptoms that might be due to AAA.
The task force noted that, since patients cannot benefit from screening and subsequent surgery unless they have a reasonable life expectancy, people over age 75 years are less likely than those who are younger to benefit from screening.
USPSTF recommended neither for nor against abdominal aortic aneurysm screening for men who have never smoked. If these men wish to consider AAA screening, the task force advised, they should consult their physicians in order to decide whether the risks are worth the potential benefits.
- Reviewed by Zalman S. Agus, MD Emeritus Professor at the University of Pennsylvania School of Medicine