Abdominal Aortic Aneurysms (AAA)

Etiology of abdominal aortic aneurysms is multifactorial but commonly involves a weakening of the arterial wall, usually by

Other causes include

Uncommonly, syphilis and localized bacterial or fungal infection, typically due to sepsis or infective endocarditis Infective Endocarditis Infective endocarditis is infection of the endocardium, usually with bacteria (commonly, streptococci or staphylococci) or fungi. It may cause fever, heart murmurs, petechiae, anemia, embolic... read more , weaken the arterial wall and cause infected (mycotic) aneurysms. Staphylococcus aureus is the number one cause of mycotic aneurysms, followed by Salmonella.

Most abdominal aortic aneurysms are asymptomatic. Symptoms and signs, when they do occur, may be nonspecific but usually result from compression of adjacent structures. As AAAs expand, they may cause pain, which is steady, deep, boring, visceral, and felt most prominently in the lumbosacral region. Patients may be aware of an abnormally prominent abdominal pulsation. Although most aneurysms grow slowly, rapidly enlarging aneurysms that are about to rupture can be tender.

The aneurysm may or may not be palpable as a pulsatile mass, depending on its size and patient habitus. The probability that a patient with a pulsatile palpable mass has a small aneurysm (ie, < 4 cm) is about 55% (positive predictive value); the probability exceeds 80% only when the mass is >5 cm in diameter (1 Symptoms and signs references Abdominal aortic diameter ≥ 3 cm typically constitutes an abdominal aortic aneurysm. The cause is multifactorial, but atherosclerosis is often involved. Most aneurysms grow slowly (~10%/year)... read more ). A systolic bruit may be audible over the aneurysm.

Patients with an occult AAA sometimes present with symptoms of complications or of the cause (eg, fever, malaise, or weight loss due to infection or vasculitis).

Most abdominal aortic aneurysms are diagnosed incidentally when they are detected during physical examination or when abdominal ultrasonography, CT, or MRI is done for other reasons. An AAA should be considered in older patients who present with acute abdominal pain or back pain whether a palpable pulsatile mass is present or not.

When symptoms or physical examination findings suggest AAA, abdominal ultrasonography or abdominal CT is usually the test of choice. Symptomatic patients should have immediate testing to make the diagnosis before catastrophic rupture. For hemodynamically unstable patients with presumed rupture, ultrasonography provides bedside results more rapidly, but intestinal gas and distention may limit its accuracy.

Laboratory tests, including complete blood count (CBC), electrolytes, blood urea nitrogen (BUN), creatinine, prothrombin time (PT), partial thromboplastin time (PTT), and blood type and cross-match, are done in preparation for possible surgery.

If rupture is not suspected, CT angiography (CTA) or magnetic resonance angiography (MRA) can more precisely characterize aneurysm size and anatomy. If thrombi line the aneurysm wall, conventional angiography may underestimate true size; CT may provide a more accurate estimate. Aortography is sometimes necessary if renal artery or aortoiliac disease is suspected or if correction with endovascular stent grafts (endografts) is being considered.

Plain abdominal x-rays are neither sensitive nor specific; however, if obtained for other purposes, x-rays may show aortic calcification outlining the aneurysm wall.

If a mycotic aneurysm is suspected, bacterial and fungal blood cultures should be done.

Screening men age > 65 years with abdominal ultrasonography decreases mortality, but the absolute reduction is small for men who are otherwise at low risk. Screening also can also provoke anxiety, particularly for aneurysms managed expectantly. Some authorities recommend shared decision-making.

Some abdominal aortic aneurysms enlarge at a rate of 10%/year. Enlargement often occurs in a stepwise pattern with periods of no growth observed. Other aneurysms enlarge exponentially.

Control of atherosclerotic risk factors, especially smoking cessation Smoking Cessation Most smokers want to quit and have tried doing so with limited success. Effective interventions include cessation counseling and drug treatment, such as varenicline, bupropion, or a nicotine... read more and use of antihypertensive medications Drugs for Hypertension A number of drug classes are effective for initial and subsequent management of hypertension: Adrenergic modifiers Angiotensin-converting enzyme (ACE) inhibitors Angiotensin II receptor blockers... read more as appropriate, is important. If a small (< 4 cm) or moderate-sized (between 4 and 5 cm) aneurysm becomes > 5.0 to 5.5 cm and if risk of perioperative complications is lower than estimated risk of rupture, AAA repair is indicated. Risk of rupture versus that of perioperative complications should be discussed frankly with the patient.

The need for surgical treatment is related to aneurysm size, which is linked to the risk of rupture (see table ).

Ruptured abdominal aortic aneurysms require immediate open surgery or endovascular stent grafting. Without treatment, mortality rate approaches 100%. There is no clear difference in mortality for open surgical treatment compared with endovascular stent grafting (1 Treatment reference Abdominal aortic diameter ≥ 3 cm typically constitutes an abdominal aortic aneurysm. The cause is multifactorial, but atherosclerosis is often involved. Most aneurysms grow slowly (~10%/year)... read more ). Mortality remains high because many patients have coexisting coronary, cerebrovascular, and peripheral atherosclerosis.

Patients who present in hemorrhagic shock require fluid resuscitation Fluids Almost all circulatory shock states require large-volume IV fluid replacement, as does severe intravascular volume depletion (eg, due to diarrhea or heatstroke). Intravascular volume deficiency... read more and blood transfusions, but mean arterial pressure should not be elevated to > 70 to 80 mm Hg (permissive hypotension) because bleeding may increase. Preoperative blood pressure control and avoidance of hypertension are important.

Elective surgical repair is recommended for

Additional indications for elective surgery include

Before elective repair, clinical consideration of coronary artery disease Overview of Coronary Artery Disease Coronary artery disease (CAD) involves impairment of blood flow through the coronary arteries, most commonly by atheromas. Clinical presentations include silent ischemia, angina pectoris, acute... read more (CAD) is often needed and may or may not require further evaluation (see table ) because some patients with an abdominal aortic aneurysm have significant risk of cardiovascular events. Aggressive medical treatment and risk factor control are essential. Routine preoperative coronary angioplasty or bypass surgery has not been shown to be necessary in most patients who can be prepared with good medical management before aneurysm repair; coronary revascularization should be considered only in patients with unstable coronary artery disease (eg, acute coronary syndrome, including unstable angina) or multiple risk factors for coronary artery disease.

Surgical repair consists of replacing the aneurysmal portion of the abdominal aorta with a synthetic graft. If the iliac arteries are involved, the graft must be extended to include them. If an aorto-bifemoral repair is done, it is important to ensure flow to at least one internal iliac artery (hypogastric artery) to avoid vasculogenic erectile dysfunction and pelvic ischemia. If the aneurysm extends above the renal arteries, the renal arteries must be reimplanted into the graft, or bypass grafts must be created.

Placement of an endovascular stent graft within the aneurysmal lumen via the femoral artery is a less invasive alternative that has been shown to have lower acute morbidity and mortality than open repair. This procedure excludes the aneurysm from systemic blood flow and reduces risk of rupture. The aneurysm eventually thromboses, and 50% of aneurysms decrease in diameter. Short-term results are good, and long-term results are favorable. Complications include angulation, kinking, thrombosis, migration of the stent graft, and endoleak (persistent flow of blood into the aneurysm sac after endovascular stent graft placement). Thus, follow-up visits must be more frequent after endovascular stent graft placement than after a surgical repair. If no complications occur, imaging tests are recommended at 1 month, 6 months, 12 months, and every year thereafter. Complex anatomy (eg, short aneurysm neck below renal arteries, severe arterial tortuosity) makes routine endovascular stent grafting difficult in these patients; however, devices have been developed to overcome these issues. In general, for a successful endovascular repair, surgeons should choose a specific device that is appropriate for the patient's anatomic characteristics.

In most cases, repair of aneurysms < 5 cm does not appear to increase survival. Because patients vary in size, it is more precise to offer repair when the aneurysm is larger than twice the diameter of an area of normal aorta in that patient. Aneurysms should be monitored with ultrasonography or abdominal CT every 6 to 12 months for expansion that warrants treatment.

Treatment of a mycotic aneurysm consists of vigorous antimicrobial therapy directed at the pathogen, followed by excision of the aneurysm. Early diagnosis and treatment improve outcome.