Abdominal aortic aneurysm (AAA) is the abnormal dilatation of the infrarenal abdominal aorta of 3.0 cm or more.¹ It occurs when the abdominal aortic wall weakens, causing it to bulge or balloon, resulting in permanent and progressive focal dilatation of the abdominal aorta² (Figure 1). AAA is the 14th leading cause of mortality in the United States, resulting in 4,500 deaths each year.³ Approximately 45,000 surgeries for AAA repair are performed annually.^1,3 AAA affects about 1.5% of men older than 60 years and 1% of women older than 64 years.⁴ Women are known to have worse outcomes with AAA than men. This is likely due to the lack of screening and late presentation associated with larger aneurysms that tend to grow faster and have a four times higher risk of rupture at diameters of 5.0 cm to 5.9 cm.⁵ The average annual risk of rupture for aneurysms that are 6.0 cm or larger is more than 10%.⁶ A ruptured AAA is associated with high mortality rates. Between 59% and 83% of patients die before they reach a hospital or have surgery.¹

A history of smoking is responsible for 75% of AAAs.⁷ In 2005, the U.S. Preventive Services Task Force (USPSTF) recommended one-time ultrasonography to screen for AAA in men 65 to 75 years of age who had ever smoked. This recommendation was updated in 2014 and 2019 and is supported by the American Academy of Family Physicians. Epidemiologic literature defines a patient with a history of smoking as someone who has smoked 100 or more cigarettes in their lifetime.⁸ Although the recommendations are stratified by men and women, the net benefit is driven by biological sex rather than gender identity.

Pathophysiology

AAA occurs from the degenerative process of smooth muscle cell loss and structural deterioration of the aortic wall, specifically within the elastic media and adventitia.⁹ Matrix metalloproteinase, a proteolytic enzyme released by T and B lymphocytes, macrophages, and other chronic inflammatory cells, destroys the elasticity and collagen of smooth muscle.^10,11

Risk Factors

Cigarette smoking is the greatest risk factor for developing AAA. Other risk factors include a family history of AAA and conditions that are associated with cardiovascular disease such as hypertension, coronary artery disease, atherosclerosis, and stroke (Table 1).^6,12 Although diabetes mellitus alone is not a risk factor for AAA, when associated with coronary artery disease and peripheral artery disease, it is linked to AAA growth and rupture.¹³

Presentation

Most AAAs are asymptomatic until they rupture, although some may be identified during an evaluation of abdominal symptoms. AAA is often detected as an incidental finding when ultrasonography, computed tomography of the abdomen, or magnetic resonance imaging is performed for other purposes. For patients who present with unexplained abdominal discomfort, such as pain that radiates to the back, flank, and groin, abdominal palpation is reasonably accurate in diagnosing AAA and does not increase the risk of rupture.¹² One study reported that the sensitivity of abdominal palpation increases significantly with AAA diameter, ranging from 29% for aneurysms 3.0 cm to 3.9 cm, 50% for those 4.0 cm to 4.9 cm, and 75% for those 5.0 cm or larger.¹⁴ The most common finding on the abdominal examination is a pulsatile mass around the umbilicus. A bruit can sometimes be heard on the pulsatile mass. Patients with popliteal artery aneurysms have a high prevalence of AAA and vice versa.¹⁵ Therefore, examining both popliteal arteries and the abdominal aorta is important when an arterial aneurysm is suspected. One study found that abdominal obesity can decrease the sensitivity of palpation.¹⁴ Physical examination has been used in practice but has low sensitivity (39% to 68%) and specificity (75%) and is not recommended for screening in patients who are obese.