Abdominal Aortic Aneurysm

Description

• Focal dilation of the aortic wall with an increase in diameter by at least 50% (>3 cm)
• 95% are infrarenal
• Rapid expansion or rupture causes symptoms
• Rupture can occur into the intraperitoneal or retroperitoneal spaces
• Intraperitoneal rupture is usually immediately fatal (20% of ruptured AAA)
• Average growth rate of 0.2–0.5 cm/yr
• Of ruptures:
  • 90% overall mortality
  • 80% mortality for patients who reach the hospital
  • 50% mortality for patients who undergo emergency repair
• Of patients who have had endovascular aortic aneurysm repair (EVAR), persistent bloodflow into the aneurysm sac can lead to continued aneurysm growth and rupture

• Risk increases with advanced age
• Present in:
  • 4–8% of all patients older than 65 yr
  • 5–10% of men 65–79 yr old
  • 12.5% of men 75–84 yr old
  • 5.2% of women 75–84 yr old

Etiology

• Risk factors are similar to other vascular diseases:
  • Male gender
  • Age >65 yr
  • Family history
  • Cigarette smoking
  • Atherosclerosis
  • HTN
  • Diabetes mellitus
  • Connective tissue disorders:
    • Ehlers–Danlos syndrome
    • Marfan syndrome
• Uncommon causes:
  • Blunt abdominal trauma
  • Congenital aneurysm
  • Infections of the aorta
  • Mycotic aneurysm secondary to endocarditis
• Rupture risk factors:
  • Size (annual rupture rates):
    • Aneurysms 5–5.9 cm = 4%
    • Aneurysms 6–6.9 cm = 7%
    • Aneurysms >7 cm = >20%
    • Expansion:
    • A small aneurysm that grows >0.5 cm in 6 mo is at high risk for rupture
  • Gender:
    • For aneurysms 4.0–5.5 cm, women have 4× higher risk of rupture compared to men with similar-sized aneurysms

Signs and Symptoms

• Abdominal, back, or flank pain:
  • Vague, dull quality
  • Constant, throbbing, or colicky
  • Acute, severe, constant
  • Radiates to chest, thigh, inguinal area, or scrotum
  • Flank pain radiating to the groin in 10% of cases
• Lower-extremity pain
• Syncope, near-syncope
• Unruptured are most often asymptomatic

• Unruptured:
  • Abdominal mass or fullness
  • Palpable, nontender, pulsatile mass
  • Intact femoral pulses
• Ruptured:
  • Classic triad (only 1/3 of the cases):
    • Pain
    • Hypotension
    • Pulsatile abdominal mass
  • Systemic:
    • Hypotension
    • Tachycardia
    • Evidence of systemic embolization
  • Abdomen:
    • Pulsatile, tender abdominal mass
    • Flank ecchymosis (Grey Turner sign) indicates retroperitoneal bleed
    • Only 75% of aneurysms >5 cm are palpable
    • Abdominal tenderness
    • Abdominal bruit
    • GI bleeding
  • Extremities:
    • Diminished or asymmetric pulses in the lower extremities
• Complications:
  • Large emboli: Acute painful lower extremity
  • Microemboli: Cool, painful, cyanotic toes (“blue toe syndrome”)
  • Aneurysmal thrombosis: Acutely ischemic lower extremity
  • Aortoenteric or aortoduodenal fistula: GI bleeding

Essential Workup

• Unstable patients:
  • Bedside abdominal US
  • Explorative surgery without further ancillary studies
• Stable, symptomatic patients:
  • Abdominal CT

Diagnostic Tests and Interpretation

• Type and cross-match blood
• CBC
• Creatinine
• Urinalysis
• Coagulation studies

• Abdominal ultrasound:
  • 100% sensitive and 92–99% specific for detecting AAA prior to rupture
  • Sensitivity has been reported as low as 10% following rupture
  • Ultrasound findings consistent with AAA are enlarged aorta >3 cm or focal dilatation of the aorta
  • Aortic thrombus can lead to the appearance of a normal-caliber aorta. Measuring from outside to outside of the aortic wall can prevent undermeasurement
  • Ultrasound is very limited in the evaluation of patients who have previously had an EVAR, strongly consider CT imaging and expert consultation
• Abdominal CT scan:
  • Contrast is not necessary to make the diagnosis but CT angiogram is required for surgical planning for an endovascular approach
  • Will demonstrate both aneurysm and site of rupture (intraperitoneal vs. retroperitoneal)
  • Allows more accurate measurement of aortic diameter

Differential Diagnosis

• Other abdominal arterial aneurysms (i.e., iliac or renal)
• Aortic dissection
• Renal colic
• Biliary colic
• Musculoskeletal back pain
• Pancreatitis
• Cholecystitis
• Appendicitis
• Bowel obstruction
• Perforated viscus
• Mesenteric ischemia
• Diverticulitis
• GI hemorrhage
• Aortic thromboembolism
• Myocardial infarction
• Addisonian crisis
• Sepsis
• Spinal cord compression

Pre Hospital

• Establish 2 large-bore IV lines
• Rapid transport to the nearest facility with surgical backup
• Alert ED staff as soon as possible to prepare the following:
  • Operating room
  • Universal donor blood
  • Surgical consultation

Initial Stabilization/Therapy

• 2 large-bore IV lines
• Cardiac monitor
• Hypotensive resuscitation

Ed Treatment/Procedures

• Emergent surgical consult and operative intervention
• Laparotomy versus endovascular aortic repair (EVAR) by vascular surgeon
• Diagnostic tests should not delay definitive treatment

Disposition

Admission Criteria
All patients with symptomatic AAA require emergent surgical intervention and admission

Discharge Criteria
Asymptomatic patients only

Follow-Up Recommendations

• Close vascular surgery follow-up must be arranged prior to discharge
• Instructions to return immediately for:
  • Any pain in the back, abdomen, flank, or lower extremities
  • Any dizziness or syncope

See Also

• Aortic Dissection
• Peripheral Artery Disease