Abdominal Aortic Aneurysm

Amit K. Jain, M.D.
Pranav M. Patel, M.D.

Basic Information

Definition

An abdominal aortic aneurysm (AAA) is a focal full-thickness dilation of the abdominal aortic artery to at least 1.5 times the diameter measured at the level of the renal arteries, or exceeding the normal diameter of the abdominal aorta by 50%. The normal diameter at the renal arteries is 2 cm (range 1.4-3.0 cm), and a diameter 3 cm or larger is generally considered aneurysmal.

ICD-10CM CODES
I71.4	Abdominal aortic aneurysm, without rupture
I71.3	Abdominal aortic aneurysm, ruptured

Epidemiology & Demographics

•

Approximately 15,000 deaths/year in the United States are attributed to AAA.
•

AAA is predominantly a disease of older adults, affecting men more than women (4:1).
•

The prevalence rate ranges from 4% to 9% in men in developed countries.
•

Clinically important AAAs ≥4 cm are present in 1% of men between age 55 and 64; and the prevalence rate increases by 2% to 4% per decade thereafter.
•

The peak incidence is among men approximately 70 years old.
•

The frequency is much higher in smokers than in nonsmokers (8:1); and the risk decreases with smoking cessation.
•

Risk factors for AAA are similar to those for other atherosclerotic cardiovascular diseases. They include age, Caucasian race, smoking, male gender, family history, hypertension, hyperlipidemia, peripheral vascular disease, and aneurysm of other large vessels.
•

AAA is two to four times more common in first-degree male relatives of known AAA patients.
•

A decreased risk of AAA is associated with female gender, non-Caucasian race, and diabetes.
•
Rupture of the AAA occurs in 1% to 3% of men age 65 or older.
1. 1.
  
  Rupture is the 10th leading cause of death in men older than age 55.
2. 2.
  
  Mortality from rupture is 70% to 95%.
3. 3.
  
  Risk factors for rupture include cardiac or renal transplants, severe obstructive lung disease, uncontrolled blood pressure, female sex, and ongoing tobacco use.
•

A recent decline in incidence and prevalence of AAA and related mortality has been attributed to reductions in tobacco use.

Etiology

•
Exact etiology is unknown and is likely multifactorial.
1. 1)
  Degenerative:
  1. a.
    
    Alterations in vascular wall biology leading to a loss of vascular structural proteins and wall strength.
  2. b.
    
    The most common association is atherosclerosis. It is uncertain whether atherosclerosis causes or results from AAAs.
  3. c.
    
    Tobacco use: >90% of people who develop an AAA have smoked at some point in their lives.
2. 2)
  
  Inherited: Familial clusters are common. High familial prevalence rate is notable in male individuals. The nature of the genetic disorder is unclear but may be linked to alpha-1-antitrypsin deficiency or X-linked mutation. Connective tissue disorders, such as Marfan’s syndrome and Ehlers-Danlos syndrome, have also been strongly associated with AAA.
3. 3)
  
  Inflammatory: AAA is a progressive inflammatory disease of the artery walls. Activated B lymphocytes promote AAA by producing immunoglobulins, cytokines, and matrix metalloproteinases (MMPs), resulting in the activation of macrophages, mast cells (MCs), and complement pathways that lead to the degradation of collagen and matrix proteins and to aortic wall remodeling.
4. 4)
  
  Infection, mycotic: syphilis, Salmonella.

Natural History

•

AAAs tend to develop in the infrarenal aorta and to expand, on average, at a rate of 0.3 to 0.4 cm per year.
•

The risk of aneurysmal rupture is largely influenced by aneurysm size, rate of expansion, and sex. Other factors associated with increased risk for rupture include continued smoking, uncontrolled hypertension, and increased wall stress.
•

Higher tension in the abdominal aorta (together with histopathologic changes such as accumulation of foam cells, cholesterol crystals, and matrix metalloproteinases) renders the abdominal aortic wall more susceptible to dilation and subsequent rupture.
•

The 5-year rupture rate of asymptomatic AAAs is 25% to 40% for aneurysms >5.0 cm in diameter, 1% to 7% for AAAs 4.0 to 5.0 cm, and nearly 0% for AAAs <4.0 cm. The likelihood that an aneurysm will rupture is increased in aneurysms with a diameter >5.5 cm; this size also demonstrates a faster rate of expansion (>0.5 cm over 6 months) and is more likely to be found in those who continue to smoke and in females.
•

Mortality rate after rupture can be as high as 90% because most patients do not reach the hospital in time for surgical repair. Of those who reach the hospital, the mortality rate is still 50%, compared with the 1% to 4% mortality rate for elective repair of a nonruptured AAA. The U.S. Preventive Services Task Force (USPSTF) also concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for AAA in women aged 65 to 75 who ever smoked and recommends against routine screening in women who never smoked (most recent update in June 2014).

Screening and Monitoring

•

The USPSTF recommends one-time screening for AAA by ultrasonography in men ages 65 to 75 who have a history of smoking, and in those 60 years of age or older with a history of AAA in a parent or sibling. These populations have been shown to have a higher prevalence of AAA, and selectively screening this group has been shown to decrease AAA-specific mortality.
•

The USPSTF has found little benefit in repeat screening in men with a negative ultrasound and has determined that men over the age of 75 are unlikely to benefit from screening. It was also concluded that the current evidence is insufficient to assess the balance of the harms and benefits of screening for AAA in women ages 65 to 75 who have ever smoked.
•

Monitoring by ultrasound or CT scan should be performed every 6 to 12 months for patients with AAAs measuring 4.0 to 5.4 cm in diameter and by ultrasound every 2 years for those with AAAs measuring <4 cm.

Physical Findings & Clinical Presentation

•

Most aneurysms are asymptomatic and incidentally discovered on imaging studies; however, symptomatic aneurysms are at an increased risk for rupture.
•

Physical examination has a sensitivity of 76% for detecting AAAs >5 cm and only 29% for AAAs 3.0-3.9 cm. The accuracy of the physical examination is markedly diminished by obese body habitus.
•

Symptomatic patients may present with abdominal, back, flank, or groin pain.
•

A pulsatile epigastric mass that may or may not be tender may be present.
•

Abdominal pain radiating to the back, flank, and groin.
•

Abdominal bruits can be present in case of renal or visceral arterial stenosis.
•

Common iliac arteries can be aneurysmal and palpable in the lower abdominal quadrants. In addition, prominent femoral and popliteal pulses warrant an abdominal ultrasound and lower extremity ultrasound.
•

Early satiety, nausea, and vomiting may be caused by compression of adjacent bowel.
•

Venous thrombosis or insufficiency may occur from iliocaval venous compression.
•

Thromboembolization can cause lower extremity pain and discoloration.
•

Ureteral obstruction and hydronephrosis can cause flank and groin pain and lead to obstructive renal failure.
•

Rupture classically presents as a triad of abdominal or back pain, hypotension, and a pulsatile abdominal mass in 50% of patients.
•

Acute blood loss may lead to myocardial infarction; arteriovenous fistulas may present as heart failure; aortoenteric fistulas may present as hematemesis or melena associated with abdominal and back pain.

Diagnosis

Differential Diagnosis

Almost 75% of patients with AAA are asymptomatic, and the condition is discovered on routine examination or serendipitously when ordering studies for other symptoms. Diagnosis of AAA should be considered in the differential of the following symptoms: abdominal pain, back pain, and/or pulsatile abdominal mass.

Laboratory Tests

Not routinely indicated. For suspected infected or inflammatory aneurysms, WBC, ESR/CRP, and blood cultures can be considered. An elevated D-dimer may indicate a thrombus within the aneurysm. Fig. 1 describes an algorithm for the diagnosis and treatment of abdominal aortic aneurysms.

FIG.1

Algorithm for the diagnosis and treatment of abdominal aortic aneurysms (AAAs).

BP, Blood pressure; CT, computed tomography; *MRI*, magnetic resonance imaging; NS, normal saline; *PRBCs*, packed red blood cells; *SBP*, systolic blood pressure; US, ultrasonography.

From Adams JG et al.: *Emergency medicine, clinical essentials*, ed 2, Philadelphia, 2013, Elsevier.

Imaging Studies

•

Abdominal ultrasound (Fig. 2) has nearly 100% sensitivity and specificity in identifying an aneurysm and estimating the size to within 0.3 to 0.4 cm. It is not accurate in estimating the extension to the renal arteries or the iliac arteries.

FIG.2

Transverse image of an abdominal aortic aneurysm.

Note the measurements of 3.33 × 3.85 cm. The inferior vena cava is seen to the patient’s right of the aorta, and the vertebral body is seen below the two vessels. Note also that there appears to be an echogenic flap within the aorta, possibly representing an aortic dissection.

From Adams JG et al.: Emergency medicine, clinical essentials, ed 2, Philadelphia, 2013, Elsevier.
•

Computed tomography (CT) (Fig. 3) scan is recommended for preoperative aneurysm imaging and estimates the size of the AAA to within 0.3 mm. There are no false-negative results, and the scan can localize the extent to renal vessels with more precision than ultrasound. It is the imaging modality of choice for symptomatic AAA. Intravenous contrast is not required to establish a diagnosis of ruptured AAA. CT can also detect the integrity of the wall (Fig. 4) and exclude rupture.

FIG.3

Three-dimensional CT image illustrates the presence of an infrarenal abdominal aortic aneurysm.

An, Aneurysm; CIA, common iliac artery; EIA, external iliac artery; IIA, internal iliac artery; IN, infrarenal neck; LK, left kidney; RA, renal artery; RK, right kidney.

From Townsend CM et al. [eds]: Sabiston textbook of surgery, ed 17, Philadelphia, 2004, Saunders.

FIG.4

Aneurysm of the abdominal aorta.

A large aortic aneurysm is evident. The aorta exceeds 5 cm in diameter. A large amount of thrombus (T) partially surrounds the contrast-enhanced patent lumen (L). Note the atherosclerotic calcification (arrowhead) in the wall of the aneurysm.
•

Magnetic resonance angiography (MRA) may also be used and is at least as accurate as CT.
•

Plain radiographs may show the outline of an aneurysm in calcified aortas. This is an insensitive test for diagnosing AAA.
•

Diagnostic aortography has essentially been replaced by other noninvasive imaging modalities such as CT or MR angiography. Intraoperative angiography is still used for determining treatment options and post-procedure efficacy (Fig. 5).

FIG.5

A, Conventional catheter angiography with bilateral marked catheters in place demonstrates a large, lobulated, infrarenal aortic aneurysm (arrowhead) with a 4-cm proximal neck suitable for endovascular repair. B, An image after endovascular repair demonstrates complete exclusion of the aneurysm (arrowhead) with no endoleak and preservation of the renal and hypogastric arteries.

Soto JA, Lucey BC: Emergency radiology: the requisites, ed 2, Philadelphia, 2017, Elsevier.
•

Endovascular aneurysm repair (EVAR) needs a close and lifelong imaging surveillance for a timely detection of possible complications, including endoleaks, graft migration, fractures, and enlargement of aneurysm sac size with eventual rupture. Contrast-enhanced computed tomography (CTA) is considered the gold standard in EVAR follow-up, but it is accompanied with radiation burden and renal injury because of the use of contrast media. In the past 2 decades, several studies have shown the role of contrast-enhanced ultrasonography (CEUS) in post-EVAR surveillance, with very good diagnostic performance, absence of renal impairment, and no radiation, accompanied by low costs, in comparison with CTA. In numerous prospective studies and meta-analyses, the detection and characterization of endoleaks with CEUS is comparable to that of CTA imaging.

Treatment

Nonpharmacologic Therapy

•

Despite lack of data substantiating reduction in expansion rate through treatment of cardiac risk factors, nonpharmacologic treatment continues to focus on risk factor modification (most importantly smoking cessation, diet, and exercise).
•

Serial studies have shown that expansion rates are faster in current smokers than in former smokers. Patients with known AAA or a family history of aneurysms should be advised to stop smoking and be offered smoking cessation interventions.
•

Definitive treatment depends on the size of the aneurysm (see “Chronic Rx”).

Acute General Rx

•

Acute symptomatic or ruptured AAA can be treated with open surgical or endovascular aneurysm repair (EVAR). The choice is determined by anatomic considerations, operative risks, and availability of regular patient follow-up for EVAR.
•

Emergent open repair has been the traditional method of treatment. However, multiple trials including Impact of Managed Pharmaceutical care on Resource utilization and Outcomes in Veterans affairs medical centers (IMPROVE) study have shown lower mortality and shorter hospital stay with EVAR. More centers are increasingly using endovascular repair for patients who fit certain anatomic and physiologic criteria.
•

However, a recent Cochrane meta-analysis for EVAR versus open repair for ruptured abdominal aortic aneurysm failed to show a difference in 30-day mortality between EVAR versus open repair. Further, long-term data on outcomes were lacking and should be the focus of future clinical trials.
•

The major limitations for EVAR include anatomical issues such as tortuosity or small caliber iliac arteries and inability to follow up patients to exclude late failure of stent-grafts and development of endoleaks.

Chronic Rx

•

Blood pressure and fasting lipids should be monitored and controlled as recommended for patients with atherosclerotic disease. Statins are associated with decreased mortality after successful AAA repair, and are recommended for those with known AAA to reduce the progression of atherosclerosis and overall cardiovascular risk.
•

The most commonly used predictor of rupture is the maximum diameter of the AAA.
•

Monitoring by ultrasound or CT scan should be performed every 6 to 12 months for patients with AAAs measuring 4.0 to 5.4 cm in diameter and by ultrasound every 2 years for those with AAAs measuring 3 to 4 cm and every 5 years for those with AAAs between 2.6 and 2.9 cm.
•

Long-term beta-blocker therapy has slowed the rate of aortic dilation and decreased the incidence of aortic complications in patients with Marfan’s syndrome. Several studies have also suggested that beta-blocker therapy may reduce the rate of expansion and risk of rupture; however, conclusive evidence is lacking.
•

A recent multicenter study of 5362 patients with AAA found no significant association between AAA progression and the use of statins, beta-blockers, angiotensin-converting enzyme inhibitors, or angiotensin II receptor blockers.
•

Antibiotics such as doxycycline and roxithromycin have been shown to limit the expansion of small AAAs.
•

Surgical repair to eliminate the risk for rupture should be performed for patients with infrarenal or juxtarenal AAA of approximately 5.5 cm or larger in diameter. All patients who are symptomatic should undergo repair, regardless of size. Timing of repair in symptomatic unruptured AAA is still under debate.
•

There is no clear advantage to early repair (open or endovascular) for small AAAs (less than 5.5 cm).
•

Percutaneous, endovascular, stent-anchored grafts placed with the patient under local anesthesia have provided an alternative approach (Fig. 6) for patients with favorable anatomy. In patients who have undergone endovascular repair, long-term surveillance is required to assess for an endoleak, stent migration, change in aneurysm size, and need for re-intervention.

FIG.6

Endovascular abdominal aortic aneurysm repair involves aneurysm exclusion with an endoluminal aortic stent-graft introduced remotely, usually through the femoral artery.

An endovascular graft extends from the infrarenal aorta to both common iliac arteries, preserving the flow to the internal iliac arteries. CIA, Common iliac artery; IIA, internal iliac artery; IN, infrarenal aortic neck; LK, left kidney; RK, right kidney; SA, suprarenal aorta.

From Townsend CM et al. [eds]: Sabiston textbook of surgery, ed 17, Philadelphia, 2004, Saunders.
•

Fenestrated endovascular repair is an alternative to open repair in the management of juxtarenal aortic aneurysms (JRAs) and short-neck abdominal aortic aneurysms. Contemporary literature shows that it is a safe and efficacious treatment, particularly for those deemed surgically high risk. Growing experience and innovation of stent-grafts are essential for the advancement of fenestrated grafting.
•

Randomized trials have shown that endovascular repair of AAA is associated with a significantly lower operative mortality than open surgical repair but it has increased rates of graft-related complications and reintervention, and is more costly. There are no differences between endovascular repair and open surgical repair in total mortality or aneurysm-related mortality at 7 years.
•

Compared with open aneurysm repair, EVAR is associated with better health-related quality of life up to 12 months postoperatively for unruptured aneurysms.
•

Most recent meta-analysis concludes that EVAR has lower rates of 30-day mortality, 30-day MI, and length of hospital stay in both elective and emergency AAA repair.
•

Based on current data, less than 2% of endovascular repairs require open conversion, and approximately half of all early endoleaks resolve spontaneously within a period of 30 days.
•

Open repair still represents a valuable solution for many patients with failed EVAR with relatively low mortality rates when performed electively.
•

Perioperative mortality is significantly less for EVAR compared with open repair (1.8% vs. 4.3%), whereas overall cumulative long-term mortality is similar (9.3 vs. 8.9 deaths) based upon the data obtained from the EVAR-1 trial.
•

In high-risk patients undergoing AAA repair, specifically those with coronary artery disease or those with more than one clinical risk factor based on the American Heart Association (AHA) guidelines, preoperative administration of beta-blockers titrated to a goal heart rate of 60 have been shown to decrease incidence of death from cardiac causes or nonfatal myocardial infarctions.
•

Patients with chronic obstructive pulmonary disease (COPD) are at higher risk for major clinical complications, particularly if the COPD is suboptimally managed or if it is present in conjunction with cardiac or renal disease. Smoking cessation for 2 months before surgery has also been shown to decrease pulmonary morbidity.
•

Renal dysfunction is a strong predictor of mortality, showing up to as high as 41% mortality in those with impaired renal function compared with 6% in those without renal dysfunction.

Referral

•

Vascular surgical referral should be made in asymptomatic patients with AAAs that are approximately 4.5 cm.
•

In patients with an expansion rate of 0.6-0.8 cm/year, it is reasonable to offer repair, although small studies have shown that using expansion as a criterion for surgical referral is of unclear benefit.
•

It is important to optimize any comorbid conditions before surgical referral.

Pearls & Considerations

•

Repairing asymptomatic AAAs smaller than 5.5 cm has not been shown to improve survival because the risk of rupture is lower than the risk of surgery.
•

The results from multiple trials to date demonstrate no advantage to immediate repair for small AAA (4.0-5.5 cm), regardless of whether open or endovascular repair is used and, at least for open repair, regardless of patient age and AAA diameter. Thus, neither immediate open nor immediate endovascular repair of small AAAs is supported by the currently available evidence.
•

Five-year survival remains poor after elective AAA repair despite advances in short-term outcomes and is associated with AAA diameter and patient age at the time of surgery. Research in this field should attempt to improve the life expectancy of patients with repaired AAA and to optimize patient selection.

Comments

•

Most AAAs are infrarenal.
•

Surgical risk is increased in patients with coexisting coronary artery disease, pulmonary disease, or chronic renal failure. Evaluation for ischemia and aggressive perioperative hemodynamic monitoring help identify high-risk patients and decrease postoperative complications.
•

It is estimated that AAAs at <5 cm expand at a rate of 0.3 to 0.4 cm/year.

Ferri – Abdominal Aortic Aneurysm