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Aneurysm of the Abdominal Aorta
Michael J. Gray, MD, MA, MS, ATC
image BASICS
DESCRIPTION
  • An infrarenal aorta ≥3 cm in diameter is considered aneurysmal (1,2,3,4,5).
  • Types
    • Fusiform aneurysm: involves the whole circumference or wall of the artery
    • Saccular aneurysm: does not involve the full circumference; often appears as an asymmetrical bleb or blister on side of aorta
  • Clinical presentation relates to aneurysm location, size, type, and comorbid factors affecting patient. The majority are asymptomatic but may present with rupture, embolism, or thrombosis. Treatment and indications for surgical repair are dictated by risk of rupture, risk of surgical repair, and estimated patient life expectancy.
  • Second most common disease to affect the aorta (5)
  • System(s) affected: cardiovascular; neurologic; heme/lymphatic/immunologic
  • Synonym(s): aortic aneurysms; AAA
Geriatric Considerations
Incidence of AAA, risk of rupture, and operative morbidity and mortality all rise with age.
Pediatric Considerations
Rare in children; may be associated with umbilical artery catheters, connective tissue diseases, arteritides, or congenital abnormalities
EPIDEMIOLOGY
  • Frequency increases >50 years of age.
  • Predominant sex: male > female (5:1) (1)
Incidence
  • > 15,000 deaths per year in United States
  • 10th leading cause of death in men 65 to 75 years
  • 3.9-7.2% males >50 years (3)
  • 1.0-1.3% females >50 years (3)
  • Females with 2 to 4 times increased risk of rupture (6)
Prevalence
  • Depends on risk factors associated with AAA
  • Prevalence of AAAs 2.9 to 4.9 cm in diameter ranges from 1.3% for men aged 45 to 54 years to 12.5% for men 75 to 84 years. Data for women are 0% and 5.2%, respectively; however, when detected, women presented at an older age and were more likely to present with a ruptured AAA. Female sex is an independent risk factor for death from AAA (2).
ETIOLOGY AND PATHOPHYSIOLOGY
  • Vascular inflammatory degenerative disease, with major role of matrix metalloproteinases and inflammatory markers that result in aortic medial degeneration (4,6)
  • Gradual and/or sporadic expansion of aneurysm and accumulation of mural thrombus (4)
  • Mural thrombus can contribute to an area of localized hypoxia, thus, further weakening the aneurysm (4).
  • Aneurysms tend to expand over time. (Laplace law: T [wall tension] = pressure × radius. Wall tension directly related to BP and radius of artery.) When wall tension exceeds wall tensile strength, rupture occurs (2,4).
  • Average small AAA (<5.5 cm) grows at rate of 2.6 to 3.2 mm/year. Larger aneurysms grow faster rate as do aneurysms in current smokers; otherwise, no identifiable risk factors to assess which small AAAs will advance to require further intervention.
  • Annual growth rate of 2.2 mm/year average for small aneurysms but increased in smokers; decreased in diabetics (4)
  • 60-80% of AAAs between 40 and 49 mm will enlarge and require surgery in 5 years.
  • Degenerative: atherosclerotic (80%); other causes: inflammatory diseases (5%), trauma, connective tissue disorders, infection (Brucella, Salmonella, Staphylococcus, tuberculosis)
Genetics
  • Familial aggregations exist: Aneurysms may develop at an earlier age.
  • 2 times risk of AAA if first-degree relative with AAA (1,2,6)
  • 12-19% of patients with repair had first-degree relative with AAA (2).
  • Marfan syndrome
  • Ehlers-Danlos syndrome
  • Polycystic kidney disease
  • Tuberous sclerosis
RISK FACTORS
Older age, male, Northern European ethnicity, family history, smoking, hypertension (HTN), hyperlipidemia, peripheral vascular disease, peripheral aneurysms, chronic obstructive peripheral disease (COPD), obesity (2,4,5,6)
GENERAL PREVENTION
  • Address cardiovascular disease risk factors.
  • Follow screening guidelines: US screening for detection of AAA in male patients, 65 to 75 years, who have ever smoked.
COMMONLY ASSOCIATED CONDITIONS
  • HTN, myocardial infarction (MI), heart failure, carotid artery, and/or lower extremity peripheral arterial disease
  • Screening for thoracic aneurysm should also be considered.
  • 20% of patients with AAA have concurrent thoracic aneurysm (5).
image DIAGNOSIS
  • Screening: recommended one-time US for AAA in men 65 to 75 years who have EVER smoked (3)[B], selective offer one-time US in men 65 to 75 years who have NEVER smoked (3)[C]
  • U.S. Preventive Services Task Force recommends against routine screening for women who have NEVER smoked and states that there is insufficient evidence to make a recommendation for women 65 to 75 years old who have EVER smoked.
  • Most often asymptomatic: discovered during exams for other complaints (1)
  • Symptomatic: embolization, thrombosis, vague abdominal or back pain, syncope, lower extremity paralysis
  • Rupture
PHYSICAL EXAM
  • Pulsatile supraumbilical mass
  • Only 30-40% of AAA were detected by physical exam (6).
  • Physical exam will only detect 76% of aneurysms >5 cm (6).
  • 14% of AAA associated with femoral or popliteal aneurysms and 62-85% of patients with femoral or popliteal aneurysms will have an AAA (5,6); therefore, recommended AAA evaluation for all patients with known femoral or popliteal aneurysms (2)[B]
  • Vague abdominal tenderness: may radiate to the back or flank
  • Encroachment by aneurysm
    • Vertebral body erosion, gastric outlet obstruction, ureteral obstruction
    • Lower extremity ischemia secondary to embolization of mural thrombus
  • Rupture leads to tachycardia, hypotension, evidence of shock and anemia, possible flank contusion (Grey-Turner sign) (6).
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
  • If rupturing AAA is considered: complete blood chemistry (chemistries, PT/INR, PTT, type and cross), ECG
  • US: simplest and least expensive diagnostic procedure
  • Multiple studies have demonstrated high sensitivity (94-100%) and specificity (98-100%) of US (3,6).
  • Although effective in detecting AAA, US is a poor test to show leakage or rupture if bleeding is into the retroperitoneal space.
  • Surveillance of asymptomatic aneurysm
    • 2.6 to 2.9 cm: Screen at 5-year intervals (6)[C].
    • 3.0 to 3.9 cm: Screen at 3-year intervals (2)[B],(6)[C].
    • 4.0 to 5.4 cm: Screen every 6 to 12 months (2)[A].
  • CT scans are preferred preoperative study (caution with IV contrast in renal failure) (5).
  • MRI/MRA can visualize AAA but is often not possible in emergent situations.
  • Aortography does not define outer dimensions of aneurysm.
  • Abdominal x-rays can be diagnostic if calcifications exist; not a diagnostic tool of choice (1,2)
  • Ongoing research is exploring alternative diagnostic measurements, including measurement of total aortic volume versus single axial diameter measurement and measurement of total thrombus burden associated with AAA because this appears to have a greater risk association (2,4).
Follow-Up Tests & Special Considerations
  • Evaluation for coronary artery disease is appropriate prior to elective AAA repair (i.e., cardiac clearance), including stress test, echocardiography, and ECG if appropriate (1).
  • If AAA was discovered at any location, then full assessment of entire aorta including thoracic aorta and aortic valve is recommended (5)[C].
  • Since AAA patients tend to have the same risk factor profile as coronary artery disease, general preventative cardiovascular disease measures should be initiated (5)[C].
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Diagnostic Procedures/Other
DIFFERENTIAL DIAGNOSIS
  • Other abdominal masses
  • Other causes of abdominal or back pain (e.g., peptic ulcer disease, renal colic, diverticulitis, appendicitis, incarcerated hernia, bowel obstruction, GI hemorrhage, arthritis, metastatic disease, MI)
image TREATMENT
GENERAL MEASURES
  • Treat atherosclerotic risk factors (2,5)[C].
  • Medical optimization of cardiac, renal, and pulmonary conditions
  • Smoking cessation (increased rate of expansion of 20-25% with continued smoking) and exercise (2)[B]
  • Emergent treatment in unstable or symptomatic patients is immediate vascular surgery consultation, adequate IV access and resuscitation, type and cross for multiple units, and rapid bedside US.
  • Less acute treatment of AAA/prevention of rupture is elective repair and risk factor modification.
MEDICATION
  • β-Blockers should be used perioperatively in absence of contraindications (2,6)[A]; bronchodilators should be used for 2 weeks prior to repair for patients with COPD (6)[C].
  • No medication has been proven to decrease the rate of growth or rupture (5).
  • β-Blockers, statins, and aspirin may decrease risk of cardiovascular related mortality but no definitive decrease in AAA mortality (5).
  • Doxycycline, previously theorized to decreased wall inflammation, has not been shown to have any effect on AAA (5).
SURGERY/OTHER PROCEDURES
Current recommendations
  • Elective
    • 5.5-cm diameter is the threshold for repair in an “average” patient (2)[B].
    • Younger, low-risk patients with long life expectancy may prefer early repair.
    • Women or AAA with high risk of rupture: Consider elective repair at 4.5 to 5 cm.
    • Consider delayed repair in high-risk patients.
    • 5% perioperative mortality for open elective repair (2)
  • High risk of rupture
    • Expansion >0.6 cm/year
    • Smoking/COPD severe/steroids
    • Family history; multiple relatives
    • Hypertension if poorly controlled
    • Shape is nonfusiform.
  • High-risk patients for elective repair
    • Risk factors for open repair include age >70 years, COPD, chronic renal insufficiency (CRI), suprarenal clamp site, with 1-year mortality if no risk factors present of 1.2% and 67% for all four risk factors present.
    • Other poor prognostic factors include inactive/poor stamina, congestive heart failure, significant coronary artery disease, liver disease, family history of AAA.
    • Consider coronary revascularization prior to aneurysm repair if coronary artery disease (6)[B].
    • Discontinue thienopyridine (clopidogrel and others); use 10 days prior to AAA repair, and restart immediately postoperatively (6)[C].
    • Transfusion to hematocrit >28.0 if elective open repair was planned (6)[C]
  • Emergent/symptomatic repair: traditionally, open repair; however, candidates with appropriate anatomy can have endovascular repair, with an estimated mortality of 32% for endovascular versus 44% open.
  • Open repair versus endovascular repair (EVAR)
    • Open repair or EVAR in patients who are good or average surgical candidates (6)[B]
    • Open repair for patients who are unable to comply with the recommended periodic long-term surveillance (6)[B]
    • EVAR for patients at high surgical risk due to significant cardiac, pulmonary, or renal disease, but no significant mortality improvement compared with no therapy (6)[B]
    • EVAR tends to have improved procedural mortality (1.8% vs. 4.3%), but long-term mortality over 6 years is similar (7.5 deaths/patient-years for EVAR versus 7.7 deaths/patient-years for open repair), and EVAR patients require lifelong follow-up for monitoring (2,3).
INPATIENT CONSIDERATIONS
Risk of abdominal compartment syndrome after repair, 4-12%; usually associated with large fluid resuscitation
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
CT or MRI evaluation of the graft for EVAR surveillance at 1 month, 6 months, then annually (2)[B]
Patient Monitoring
BP and fasting lipid values: Control as for atherosclerotic disease (6)[C].
DIET
Low-fat, low-salt, and low-caffeine diet; nutrition optimized prior to elective repair; parenteral nutrition started within 7 days postoperatively if unable to have enteral feeds
PATIENT EDUCATION
Smoking cessation, aerobic exercise
PROGNOSIS
  • Annual risk of rupture: (1)
    • <4-cm diameter: ˜0% 4 to 4.9 cm: ˜0.5-5%
    • 5 to 5.9 cm: ˜3-15% 6 to 6.9 cm: ˜10-20%
    • 7to 7.9 cm: ˜20-40% >8 cm: 30-50%
  • Patients with AAAs measuring ≥5.5 cm should undergo repair as should all patients with symptomatic AAA. Recommended routine surveillance at 1 year and every 5 years following repair (2).
  • Only ˜18% of patients with ruptured AAA survive.
  • Despite a 5:1 ratio of AAA between males and females, women have higher AAA-associated mortality and morbidity, regardless of open or endovascular repair (2).
  • 59-83% mortality if rupture occurs prior to hospitalization (3)
REFERENCES
1. Aggarwal S, Qamar A, Sharma V, et al. Abdominal aortic aneurysm: a comprehensive review. Exp Clin Cardiol. 2011;16(1):11-15.
2. Hirsch AT, Haskal ZJ, Hertzer NR, et al. ACC/AHA 2005 practice guidelines for the management of patients with peripheral arterial disease: a collaborative report. Circulation. 2006;113(1):e463-e654.
3. LeFevre ML. Screening for abdominal aortic aneurysm: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2014;161(4):281-290.
4. Moxon JV, Parr A, Emeto TI, et al. Diagnosis and monitoring of abdominal aortic aneurysm: current status and future prospects. Curr Probl Cardiol. 2010;35(10):512-548.
5. Erbel R, Aboyans V, Boileau C, et al. 2014 ESC Guidelines on the diagnosis and treatment of aortic diseases: document covering acute and chronic aortic diseases of the thoracic and abdominal aorta of the adult. The Task Force for the Diagnosis and Treatment of Aortic Diseases of the European Society of Cardiology (ESC). Eur Heart J. 2014;35(41):2873-2926.
6. Chaikof EL, Brewster DC, Dalman RL, et al. The care of patients with an abdominal aortic aneurysm: the Society for Vascular Surgery practice guidelines. J Vasc Surg. 2009;50(4 Suppl):S2-S49.
Additional Reading
  • Rooke TW, Hirsch AT, Misra S, et al. 2011 ACCF/AHA focused update of the guideline for the management of patients with peripheral artery disease (updating the 2005 guideline): a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2011;58(19):2020-2045.
  • Sweeting MJ, Thompson SG, Brown LC, et al. Metaanalysis of individual patient data to examine factors affecting growth and rupture of small abdominal aortic aneurysms. Br J Surg. 2012;99(5):655-665.
See Also
Aortic Dissection; Ehlers-Danlos; Giant Cell Arteritis; Marfan Syndrome; Polyarteritis Nodosa; Turner Syndrome
Codes
ICD10
  • I71.4 Abdominal aortic aneurysm, without rupture
  • I71.3 Abdominal aortic aneurysm, ruptured
Clinical Pearls
  • US is the procedure of choice for screening for AAA in any male >65 years with any history of tobacco use.
  • Suspect AAA for any elderly patient with back, abdominal, or groin pain. Triad of hypotension/shock, pulsatile abdominal mass, and abdominal/back pain always suggests rupture, which requires emergent evaluation for surgery.
  • 5.5 cm is the threshold diameter for elective surgical treatment (with some exceptions).