Most unruptured AAAs are asymptomatic and therefore go undetected. The first symptom of AAA in most patients is rupture, which is often fatal. For this reason, AAA is referred to as a silent killer. Those that are fortunately found are usually discovered incidentally in the course of a work-up for other medical problems, particularly given the increased use of imaging studies (CT, MRI, ultrasound). Rarely, as an AAA enlarges, patients can experience abdominal or lower back pain, the latter from compression of the spine. Thrombus commonly forms within the outer walls of an AAA. Though uncommon, the thrombus can embolize distally to the lower extremities.

Risk factors for AAA include smoking, age over 60, Caucasian race, male, coronary artery disease, a history of extra-abdominal aneurysm such as femoral or popliteal aneurysms, atherosclerosis, family history of AAA, and hypertension. COPD is also a risk factor for AAA and is independent of smoking.

No. While diabetes is an important risk factor for intimal atheroma formation, MI, stroke, and peripheral arterial disease, it is actually protective against AAA. While the protective mechanism of diabetes is not fully understood, one hypothesis is that glycation of matrix metalloproteinases (discussed in Pathophysiology) leads to their deactivation and thus decreases aortic remodeling.

Physical examination for the detection of AAA can be useful when carefully performed. The sensitivity/specificity of the physical examination for AAA increases as the AAA size increases and decreases as the patient’s body mass index increases. Obesity is the biggest limiting factor in diagnosing an AAA on physical exam. In addition, the value of physical examination varies by practitioner and is limited in detecting smaller aneurysms.

The American College of Cardiology, American Heart Association, and the US Preventive Services Task Force recommend screening with physical exam and one-time abdominal ultrasound for men between ages 65 and 75 who have had any smoking history. First-degree relatives of a patient with AAA should be screened at age 60. If an AAA is found, it should be followed by US yearly if it is between 3 and 4 cm and biannually if between 4 and 4.5 cm.

Femoral and popliteal artery aneurysms are associated with AAA. This association is more common in males, and screening studies have identified an incidence of 14 % for either peripheral artery aneurysm. Femoral and popliteal aneurysms can sometimes be detected on physical exam. However, duplex ultrasonography is the recommended screening modality in patients found to have AAA. The main risk associated with these peripheral aneurysms is limb ischemia from thrombosis and/or distal embolization.

The normal size of the infrarenal aorta is 2.0 cm in men and 1.8 cm in women.

Although AAA is a multifactorial disease process, it ultimately leads to the degeneration of the medial layer through degradation of elastin and collagen.

For an artery to be considered an aneurysm, there must be a focal area that is 1.5 times larger than the diameter of the non-aneurysmal artery above. In the case of the infrarenal aorta, this would mean that a diameter of about 3 cm or more is considered an aneurysm.

Studies examining the annual growth rate of small AAA estimate a rate of 2–4 mm/year. Patients found to have the so-called rapid expansion (>5 mm/6 months) should be referred for elective repair. In addition, routine monitoring is important in AAA as expansion tends to be in stepwise growth spurts rather than linear.

Ongoing smoking has been found to increase growth rate of AAA, whereas patients with diabetes have slower growth rates. The use of blood pressure medications has not been shown to consistently slow the growth rates of AAA.

MMPs are important for collagen turnover, which is vital to inflammation and wound healing. Patients with AAA have abnormally high levels of MMP activity in the aortic wall, which weakens the arterial wall and contributes to the dilation of the aneurysm over time.

Family history is a risk factor for AAA. First-degree relatives of patients with AAA have up to 12 times higher risk of developing the disease, and this is increased up to 18 times in siblings of patients with AAA. Interestingly, while male gender is an independent risk factor for AAA, familial groupings of AAA tend to occur more often in female relatives.

AAA most commonly ruptures into the retroperitoneum (the aorta is a retroperitoneal structure) and most often to the left (the vena cava is on the right and may prevent rupture to that side). Free rupture into the peritoneum is rare and would likely lead to immediate death as there is no ability to tamponade the bleeding.

As the aneurysm enlarges, the risk of rupture also increases. AAA with a 4–5-cm diameter has a 0.5–5 % annual chance of rupturing versus 30–50 % in an AAA > 8 cm diameter.

Poorly controlled blood pressure, COPD (increase in systemic proteinase activity), and female gender (smaller aortas to begin with) have been associated with an increased risk of AAA rupture.