Nonmodifiable risk factors for abdominal aortic aneurysm include older age, male sex, and a family history of the disorder. Starting at 50 years of age for men and 60 to 70 years of age for women, the incidence of aneurysms increases significantly with each decade. The risk of abdominal aortic aneurysm is approximately four times as high among men as among women and four times as high among people with a family history of the disorder as among those without a family history. Smoking is the strongest modifiable risk factor. Other, less prominent risk factors for abdominal aortic aneurysm include hypertension, an elevated cholesterol level, obesity, and preexisting atherosclerotic occlusive disease.
What are the recommendations for screening for abdominal aortic aneurysms?
Ultrasonography is the primary method used for screening and is highly sensitive (95%) and specific (100%). CT scanning and magnetic resonance imaging (MRI) are expensive, incur risks (radiation exposure from CT and risks associated with intravenous contrast material), and should not be used for screening but rather reserved for preinterventional planning. The current recommendations of the U. S. Preventive Services Task Force are a one-time screening in men 65 to 75 years of age who have ever smoked (grade B recommendation) and selective screening in men 65 to 75 years of age who have never smoked (grade C recommendation). Medicare also covers screening for patients with a family history of abdominal aortic aneurysm. Data from nonrandomized studies suggest that there may be subgroups of women who benefit from screening; however, this finding has not been prospectively validated.
What are the indications for surgical repair of an abdominal aortic aneurysm?
Under most circumstances, aneurysms should not be prophylactically repaired unless they are at least 5.5 cm in diameter. Nevertheless, there are occasions when repair of small aneurysms should be considered. Symptomatic aneurysms should be immediately repaired. Pain in the abdomen, back, or flank is the most common symptom, but aneurysms can produce many other symptoms or signs (e.g., hematuria or gastrointestinal hemorrhage). The rate of growth is another important predictor of rupture; aneurysms that expand by more than 0.5 cm in diameter over a period of 6 months should be considered for repair regardless of the absolute size. The observations that aneurysms rupture at a smaller size in women than in men and that women have higher rupture-related mortality than men have led some experts to recommend a diameter of 5.0 cm as the threshold for elective intervention in women. Other factors that are associated with an increased risk of rupture and may prompt repair at a threshold of less than 5.5 cm include the presence of a saccular aneurysm (most aneurysms are fusiform) and a family history of abdominal aortic aneurysm.
What surgical techniques are available for repair of an abdominal aortic aneurysm?
Two approaches to repairing aneurysms are currently available: open repair (performed since the 1950s) and endovascular repair (first performed in 1987). Endovascular repair, a less invasive approach, involves the intraluminal introduction of a covered stent through the femoral and iliac arteries; the stent functions as a sleeve that passes through the aneurysm sac, anchoring in the normal aorta above the aneurysm and in the iliac arteries below the aneurysm. To be eligible for endovascular repair, a patient must have appropriate anatomy, including iliac vessels that are of sufficient size to allow introduction of the graft and an aortic neck above the aneurysm that allows the proximal graft to be anchored without covering the renal arteries. Thus, with existing techniques, there are some infrarenal aneurysms that are not amenable to endovascular repair. The use of endovascular repair has grown steadily in the United States, and this procedure is currently performed in more than 75% of patients undergoing surgical intervention for abdominal aortic aneurysm, with a portion of the remaining patients having unsuitable anatomy. Endovascular repair confers an initial survival benefit; however, this benefit disappears over a period of 1 to 3 years. Endovascular repair and open repair are associated with similar mortality over the long term (8 to 10 years).