The arterial wall consists of three layers: intima, media, and adventitia. Abdominal aortic aneurysms (AAA) are aneurysms that involve all three layers of the artery. Pseudoaneurysms do not include all three layers and typically occur after trauma.
AAA have the highest frequency in males. Further, smokers are eight times more likely to acquire the disease. Given the significant risk of AAA in smokers, the United States Preventive Services Task Force (USPSTF) recommends one-time screening by ultrasonography for male smokers age 65 to 75. The purpose of screening is to identify an aneurysm that is at significant risk of rupture.
AAA are diagnosed in a patient when dilation of the abdominal aorta becomes 1.5-2 times the normal diameter. Current recommendations are to treat AAA surgically in patients whose aneurysm expands to 5.5 cm or greater. The table below shows values for risk of rupture per year.
|Abdominal aortic aneurysm diameter (cm)||Risk of rupture per year (%/year)|
|< 4.0||Very rare|
Table 1. Estimated yearly risk of rupture.
AAA are thought to be due to weakening of the aortic wall from imbalances between collagen degradation and synthesis. This initial imbalance provides the structural deficit whereby genetic or diet-induced atherosclerosis or hypertension can further weaken the vessel wall. AAA are uncommon in individuals under 60. Special populations, for example individuals with Marfan’s syndrome, are predisposed to developing abdominal aortic aneurysms due to inadequate fibrillin production, which affects the vision and joints.
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