Abdominal aortic aneurysm (AAA), which is an abnormal focal dilation of the abdominal aorta, is relatively common and has the potential for significant morbidity and mortality. Most patients with AAA are asymptomatic but come to medical attention by finding of a pulsatile mass on physical examination, as the result of other abdominal imaging studies, or through ultrasound screening programs for AAA . When symptoms do occur, patients commonly present with abdominal, back, or flank pain, but thromboembolism can also occur leading to symptoms of limb ischemia. Aneurysms that produce symptoms are at an increased risk for rupture, which is associated with high mortality rates.
A diagnosis of AAA generally requires imaging confirmation that an aneurysm is present, which is most often accomplished using abdominal ultrasound. However, in symptomatic patients, computed tomography of the abdomen provides additional information that can determine if the aneurysm has ruptured, is expanding rapidly, and for those without signs of rupture, whether or not symptoms are likely to be related to the aneurysm or due to other abdominal pathology.
The clinical features and diagnosis of AAA will be reviewed here. The management of nonruptured and ruptured AAA are discussed elsewhere. (See "Management of asymptomatic abdominal aortic aneurysm", section on 'Introduction' and "Management of symptomatic (non-ruptured) and ruptured abdominal aortic aneurysm", section on 'Introduction'.)
ANEURYSM DEFINITION AND ANATOMY
An aneurysm is defined as a segmental, full-thickness dilation of a blood vessel 50 percent greater than its normal diameter [2,3]. Although “normal” diameter varies with age, gender, and body habitus, the average diameter of the human infrarenal aorta is about 2.0 cm; the upper limit of normal is typically <3.0 cm . Thus, for the majority of patients, an infrarenal aorta with a maximum diameter ≥3.0 cm is aneurysmal [2,4,5]. The normal diameter of the suprarenal aorta tends to be about 0.5 cm larger than the infrarenal aorta.
The aorta dilates with age and the normal aortic diameter in older patients tends to be larger. In a population-based study using magnetic resonance imaging to obtain aortic diameters at various levels in 70-year-old patients, the average diameters were :