Abdominal Aortic Aneurysm (Aortic Aneurysm)
An abdominal aortic aneurysm (AAA) is an abnormal bulging or widening of the abdominal aorta—the largest blood vessel in the body that supplies blood to the abdomen, pelvis, and legs. An aneurysm is defined as a focal dilation exceeding 50% of the normal vessel diameter, typically 3 cm or greater in the abdominal aorta. Most AAAs develop slowly over years and cause no symptoms, but they carry a serious risk of rupture, which is a life-threatening emergency. AAAs are most common in older adults, particularly men over 65, and screening programs have been established to detect them early.
What is it?
The aorta is the main artery carrying oxygenated blood from the heart through the chest (thoracic aorta) and abdomen (abdominal aorta) to the rest of the body. The normal diameter of the abdominal aorta is approximately 2 cm, though it varies by gender, age, and body size. An AAA develops when the aortic wall weakens and balloons outward, typically due to degenerative changes in the wall structure. The weakening involves breakdown of elastin and collagen fibers in the vessel wall, inflammation, and sometimes atherosclerotic plaque buildup. Most AAAs are fusiform (uniform widening around the entire circumference), though some are saccular (localized outpouching on one side).
AAAs are classified by size: small aneurysms measure 3.0-4.4 cm, medium aneurysms 4.5-5.4 cm, and large aneurysms 5.5 cm or greater. The risk of rupture increases exponentially with size—aneurysms under 5.5 cm have a relatively low annual rupture risk (less than 1%), while those over 7 cm have rupture rates exceeding 30% per year. Risk factors include male gender (men are 4-6 times more likely than women), age over 65, smoking (the strongest modifiable risk factor, increasing risk 5-7 fold), family history (15-25% have a first-degree relative with AAA), high blood pressure, atherosclerosis, high cholesterol, chronic obstructive pulmonary disease (COPD), and certain genetic conditions such as Marfan syndrome or Ehlers-Danlos syndrome. Most AAAs occur below the renal arteries (infrarenal), making them more accessible for surgical repair while preserving kidney blood flow.
Important to Know
Most AAAs are asymptomatic and discovered incidentally during imaging for other reasons or through screening ultrasound. When symptoms occur, they may include a pulsating sensation near the navel, deep, constant pain in the abdomen or back, or a pulsating abdominal mass felt during examination. Symptoms of rupture—a life-threatening emergency—include sudden severe abdominal or back pain, signs of shock such as rapid heart rate, low blood pressure, pale skin, lightheadedness, and loss of consciousness. Ruptured AAA has a mortality rate exceeding 80%, with most patients dying before reaching the hospital. Diagnosis is made through abdominal ultrasound for screening and initial detection, CT angiography (CTA) for detailed assessment of size, location, and anatomy when planning repair, and MRI angiography as an alternative in patients who cannot receive CT contrast. Management depends on aneurysm size and growth rate: small aneurysms (under 5.5 cm in men, 5.0 cm in women) are monitored with serial ultrasound or CT every 6-12 months; risk factor modification includes smoking cessation (most critical), blood pressure control, statin therapy, and management of other cardiovascular risk factors; elective repair is recommended for aneurysms 5.5 cm or larger in men, 5.0 cm or larger in women, or smaller aneurysms growing more than 0.5 cm per year or causing symptoms. Repair options include open surgical repair (replacing the aneurysmal segment with a synthetic graft) and endovascular aneurysm repair (EVAR, where a stent-graft is inserted through leg arteries and deployed inside the aneurysm). EVAR has lower short-term mortality and faster recovery but requires lifelong surveillance and has a higher rate of re-intervention. Emergency surgery for ruptured AAA carries high mortality (40-50% even with surgery) making elective repair of large aneurysms far preferable. Screening programs recommend one-time ultrasound screening for men aged 65-75 who have ever smoked, which has been shown to reduce AAA-related mortality by detecting aneurysms early when they can be monitored and treated electively.