Vascular: Abdominal Aortic Aneurysm (AAA)

Abdominal Aortic Aneurysm (AAA)

Basics

  • Aneurysm Definition: 1.5x Dilation of Normal Vessel Diameter
    • Normal Diameter: 2-3 cm
  • Most Common Cause: Atherosclerosis with Degeneration of Media
  • Most Common Site: Infrarenal (80%)
  • Rupture Has a 40-50% Mortality
    • Most Common Site: 2-4 cm Inferior to Renals; Left Posterolateral Wall

Risk Factors

  • Disease Risk Factors:
    • Smoking (Strongest Risk Factor)
    • Male
    • Elderly
    • Hypertension
    • White
    • Spinal Cord Injury
  • Rupture Risk Factors:
    • Hypertension
    • COPD
    • Overall Size
    • Rapid Increase in Size
    • Female Sex

Presentation

  • Mostly Asymptomatic & Found Incidentally
  • Rupture Triad:
    • Acute Abdominal or Back Pain
    • Hypotension
    • Pulsatile Abdominal Mass

Diagnosis

  • Screening: Duplex US
    • One-Time US Indications:
      • Age 65 with Tobacco History (Smoked ≥ 100 Cigarettes)
      • Age 65 with First-Degree Relatives with AAA’s
    • Surveillance Frequency (SVS Guidelines):
      • ≥ 3.0 cm: Every 3 Years
      • ≥ 4.0 cm: Every 12 Months
      • ≥ 5.0 cm: Every 6 Months
    • US is Good for AAA But Poor at Identifying Rupture
  • Surgery Planning: CTA
  • Ruptured:
    • Stable, Transient Responder or Insufficient Evidence: CTA
    • Unstable & Sufficient Clinical Evidence: Proceed Directly to Surgery

Repair Indications

  • Symptomatic
  • Large
    • Males ≥ 5.5 cm
      • ≥ 5.0 cm if High Rupture Risk (COPD, Poorly Controlled HTN)
    • Females ≥ 5.0 cm
  • Growth > 1 cm Per Year
  • Peripheral Ischemia from Embolization of Mural Thrombosis
  • Mycotic Aneurysm

Repair

  • Stable: Elective Open Repair or Endovascular Aneurysm Repair (EVAR)
    • EVAR Often Preferred (Especially if High Risk, Elderly or Multiple Comorbidities)
    • EVAR Requirements/Contraindications:
    • Comparison:
      • Similar Mortality if Ruptured
      • Short-Term (30-Day) Mortality:
        • EVAR – 2-4% (Better)
        • Open – 5-7%
      • Similar Long-Term Mortality
  • Unstable: Emergent Open Repair or Endovascular Aneurysm Repair (EVAR)
    • Allow Permissive Hypotension: SBP 50-100

AAA 1

AAA by Duplex US 2

AAA by CTA 3

Other Aortic Aneurysms

Inflammatory Aneurysm

  • Aneurysmal Dilation Due to Significant Inflammation
    • Thick Aortic Wall with Adjacent Retroperitoneal Fibrosis
    • Dense Adherence to Adjacent Structures
  • Etiology Not Entirely Understood
  • Specific Issues:
    • Adhesions to Duodenum & Small Bowel
    • Ureter Entrapment
  • Tx: Stent Grafting (Inflammation Resolves with Graft)

Mycotic Aneurysm

  • Infected Aneurysm
  • Most Common Organisms: Staphylococcus #1, Salmonella #2, Escherichia coli & Streptococcus
    • Most Common Non-Aneurysmal Infection: Salmonella
  • More Often Saccular than Fusiform
  • High Risk of Rupture
  • CT Findings:
    • Periaortic Soft Tissue Mass
    • Fluid Stranding
    • Destruction of Surrounding Tissues
  • Tx: ABX & Surgical Repair (Reconstruction or Extra-Anatomic Bypass)

References

  1. Blaus B. Wikimedia Commons. (License: CC BY-SA-4.0)
  2. Spangler R, Van Pham T, Khoujah D, Martinez JP. Abdominal emergencies in the geriatric patient. Int J Emerg Med. 2014 Oct 21;7:43.(License: CC BY-4.0)
  3. Jiber H, Hajji R, Zrihni Y, Zaghloul R, Zizi O, Bouarhroum A. Isolated infrarenal abdominal aorta aneurysm in a 42-year-old patient with Marfan’s syndrome: Case report. SAGE Open Med Case Rep. 2013 Oct 1;1:2050313X13507564. (License: CC BY-NC-3.0)