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Aneurysm of the Abdominal Aorta (AAA)

Basics

  • Two types:
  • True aneurysm: involves all three vessel wall layers.
  • False (pseudoaneurysm): intimal and medial layers disrupted; dilated segment held by adventitia only; higher rupture risk.
  • AAA is the most common true arterial aneurysm, usually infrarenal.
  • Aortic diameter β‰₯3 cm is aneurysmal.
  • Men: diameter predictive of clinical events; women: aortic scaling index (diameter/BSA) more predictive.

Epidemiology

  • Prevalence: 2-8% in developed countries; 4-8% occult AAA in older men on ultrasound.
  • 90% of AAA >4 cm related to atherosclerosis.
  • Male predominance.
  • Incidence: 15,000 deaths/year in US; 0.4-0.67% in Western populations.
  • Incidence increases with age; men 65-74: 55/100,000 patient-years, men >85: 298/100,000.
  • Mortality decreased by 50% since 1990s due to smoking decline, screening, early intervention.

Etiology and Pathophysiology

  • Degradation of elastin and collagen in aortic wall causes aneurysm formation.
  • Causes: inflammation, degenerative disorders, vasculitis, infection, trauma; majority due to atherosclerosis.
  • Natural course: progressive expansion; smoking accelerates growth.

Genetics

  • Familial AAAs: polygenic inheritance.
  • Monogenic syndromes (Marfan, Ehlers-Danlos, Loeys-Dietz) mainly cause thoracoabdominal aneurysms.

Risk Factors

  • Older age, male, Caucasian, family history, smoking, hypertension, hyperlipidemia, atherosclerosis, peripheral aneurysms, obesity.

Prevention

  • Address cardiovascular risk factors aggressively.
  • Screening recommended for men 65-75 years with smoking history.

Associated Conditions

  • Hypertension, myocardial infarction, heart failure, carotid atherosclerosis, peripheral arterial disease, tobacco abuse.
  • 20% AAA patients have concurrent thoracic aneurysm.

Diagnosis

  • Asymptomatic AAAs often found on screening.
  • USPSTF: one-time ultrasound screen for men 65-75 years with smoking history; selective screening for nonsmoking men 65-75 with risk factors; women with first-degree relative with AAA also considered.
  • Symptomatic triad: shock, pulsatile abdominal mass, abdominal pain β†’ suggest rupture; urgent surgery.
  • Imaging:
  • Ultrasound: test of choice for asymptomatic AAA (94-100% sensitivity).
  • CT with IV contrast: preferred for symptomatic patients (caution in renal failure).
  • MRI/MRA: rarely used emergently.
  • X-ray: may show calcifications.
  • Labs if rupture suspected: CBC, chemistry, coagulation, ECG.

Physical Exam

  • Pulsatile supraumbilical abdominal mass.
  • Signs of rupture: hypotension, tachycardia, shock, flank contusion (Grey Turner sign).
  • Possible vertebral erosion, ureteral obstruction, embolic ischemia to legs.

Differential Diagnosis

  • Other abdominal masses, GI or renal causes of abdominal/back pain, hernias, bowel obstruction, GI hemorrhage, arthritis, metastasis, MI.

Treatment

General Measures

  • Control atherosclerotic risk factors: HTN, dyslipidemia, diabetes, smoking cessation.
  • Smoking doubles AAA growth rate (~0.35 mm/year).
  • Emergent vascular surgery consult for unstable or symptomatic patients; IV access, resuscitation, bedside ultrasound.
  • Elective repair recommended based on size and risk factors.

Medications

  • Ξ²-blockers, aspirin, statins: may reduce AAA growth and complications; recommended for CAD risk reduction.
  • ACE inhibitors: inconclusive on growth; may reduce rupture risk.
  • Doxycycline, roxithromycin: no proven effect on AAA.

Surgery

  • Elective repair threshold: diameter β‰₯5.5 cm in average patient.
  • Consider earlier repair (4.5-5 cm) in women or high rupture risk patients.
  • High risk for rupture: rapid expansion (>0.5 cm/6 months), uncontrolled HTN, smoking, severe COPD.
  • Perioperative mortality ~5% for elective open repair.
  • Endovascular AAA repair (EVAR) preferred for ruptured AAA in high-risk patients; similar 30-day mortality to open repair.
  • Contraindications to EVAR: aortic neck >32 mm or neck length <7 mm for ruptured AAA.

Admission and Inpatient Care

  • Monitor for abdominal compartment syndrome (4-12%), especially post-large fluid resuscitation.

Follow-Up

  • Post-open repair CT at 5 years to assess late complications.
  • Tailor imaging and surveillance postoperatively.
  • Aggressive risk factor modification post-op mandatory.

Diet

  • Low-fat, low-salt, low-caffeine diet.
  • Optimize nutrition pre-elective repair.

Patient Education

  • Smoking cessation, aerobic exercise, and aggressive control of cardiovascular risk factors.

Prognosis

  • Progressive disorder; average expansion 0.3-0.4 cm/year.
  • Fast expansion >0.6 cm/year needs evaluation for surgery.
  • Rupture risk increases with diameter >5.5 cm, rapid growth, female sex, recent surgery, uncontrolled HTN.

Complications

  • MI, respiratory failure, acute kidney injury (early).
  • Graft infection, aortoenteric fistula, graft occlusion (late).
  • Ischemic bowel, abdominal compartment syndrome post-rupture and open repair.

References

  1. Chaikof EL, Dalman RL, Eskandari MK, et al. Society for Vascular Surgery guidelines on AAA care. J Vasc Surg. 2018;67(1):2-77.e2.
  2. LeFevre ML; USPSTF recommendation on AAA screening. Ann Intern Med. 2014;161(4):281-290.
  3. Guessous I, Periard D, Lorenzetti D, et al. Pharmacotherapy for AAA expansion: systematic review. PLoS One. 2008;3(3):e1895.
  4. Braithwaite B, Cheshire NJ, Greenhalgh RM, et al; IMPROVE Trial. EVAR vs open repair outcomes. Eur Heart J. 2015;36(31):2061-2069.

See Also

  • Aortic Dissection
  • Arteritis, Temporal
  • Ehlers-Danlos Syndrome
  • Marfan Syndrome
  • Polyarteritis Nodosa
  • Turner Syndrome

ICD10 Codes

  • I71.4 Abdominal aortic aneurysm, without rupture
  • I71.3 Abdominal aortic aneurysm, ruptured

Clinical Pearls

  • Men 65-75 with smoking history should have one-time ultrasound screening.
  • Screening intervals depend on aneurysm size; larger aneurysms require more frequent imaging.
  • Ruptured AAA presents with shock, abdominal pain, pulsatile mass; bedside ultrasound is vital.
  • EVAR and open repair have similar mortality but EVAR has lower perioperative morbidity.
  • Aggressive risk factor control, especially smoking cessation, is crucial.