Abdominal aortic aneurysm

Background

• Focal dilation of the abdominal aorta to >50% of normal diameter (typically >3 cm)
• Most commonly infrarenal (95%)
• Ruptured AAA is a surgical emergency with overall mortality of 65-85% (including prehospital deaths)
• For those who reach OR, mortality is still 40-50%
• Risk factors:
  • Age > 65 years, male sex (6:1 ratio), smoking (strongest modifiable risk)
  • Hypertension, family history, COPD, peripheral vascular disease
  • Connective tissue disorders (Marfan, Ehlers-Danlos)
• Risk of rupture increases with size:
  • <5 cm: ~1%/year
  • 5-6 cm: ~10%/year
  • >7 cm: ~30%/year

Clinical Features

Classic Triad of Ruptured AAA

• Abdominal/back pain + hypotension + pulsatile abdominal mass
• Present in only ~50% of cases

Presentations

• Intact (unruptured) AAA: usually asymptomatic or incidental finding
• Symptomatic unruptured: abdominal/back/flank pain (expanding aneurysm)
• Ruptured AAA:
  • Sudden, severe abdominal or back pain (may radiate to groin, flank, or thigh)
  • Hypotension / hemorrhagic shock
  • Pulsatile abdominal mass (difficult to palpate in obese or hypotensive patients)
  • May present as syncope or cardiac arrest
• Contained rupture: retroperitoneal hemorrhage may be temporarily tamponaded
  • Transient hemodynamic stability — do not be falsely reassured
• Mimics many conditions: renal colic, diverticulitis, MI, musculoskeletal back pain

Differential Diagnosis

Diffuse Abdominal pain

• Abdominal aortic aneurysm
  • Aortocaval fistula
• Acute gastroenteritis
• Aortoenteric fisulta
• Appendicitis (early)
• Bowel obstruction
  • Large bowel obstruction
    • Ogilvie's syndrome
  • Small bowel obstruction
  • Malignant bowel obstruction
• Bowel perforation
• Diabetic ketoacidosis
• Gastroparesis
• Hernia
• Hypercalcemia
• Inflammatory bowel disease
• Mesenteric ischemia
  • Mesenteric vein thrombosis
• Pancreatitis
• Peritonitis
• Sickle cell crisis
• Spontaneous bacterial peritonitis
• Volvulus

Evaluation

Bedside Ultrasound (First-Line in ED)

• POCUS is the single most important test for unstable patients
• Sensitivity ~100% for detecting aneurysm >3 cm
• Measure outer wall to outer wall in transverse view
• Cannot reliably detect rupture (free fluid may suggest it but absence does not exclude)
• US identifies the aneurysm; CT identifies the rupture

CT Angiography

• Gold standard for defining anatomy and surgical planning
• Identifies rupture, contained leak, extent, relation to renal arteries
• ONLY for hemodynamically STABLE patients
• Sensitivity for rupture approaches 100%

Labs

• Type and crossmatch (at least 6 units PRBCs)
• CBC, BMP, coagulation studies, lactate
• Do NOT delay resuscitation or imaging for labs

Management

Ruptured AAA

• Activate massive transfusion protocol
• Permissive hypotension: target SBP 70-90 mmHg
• Avoid aggressive crystalloid resuscitation; use blood products
• Emergent vascular surgery consultation
• Unstable patients go directly to OR (do NOT delay for CT)
  • EVAR if anatomy suitable and resources available
  • Open surgical repair if EVAR not feasible
• If arrest: consider REBOA or ED thoracotomy with aortic cross-clamp

Symptomatic Unruptured AAA

• Urgent vascular surgery consultation
• Blood pressure control: target SBP 100-120 mmHg
• Admit for expedited repair

Incidental Asymptomatic AAA

• <4 cm: surveillance US every 12 months
• 4-5.4 cm: surveillance US every 6 months; vascular referral
• >=5.5 cm: refer for elective repair
• USPSTF: one-time screening US for men 65-75 who have ever smoked

Disposition

• Ruptured: emergent OR / ICU
• Symptomatic unruptured: monitored bed, urgent vascular consult
• Asymptomatic incidental: outpatient vascular referral

See Also

• Aortic dissection
• Abdominal pain
• Shock
• Ultrasound: Aorta

References

• Chaikof EL, et al. SVS practice guidelines for AAA. J Vasc Surg. 2018;67(1):2-77. PMID 29268916
• Kent KC. Abdominal aortic aneurysms. N Engl J Med. 2014;371(22):2101-2108. PMID 25427112