Abdominal Aortic Aneurysm

KEY FEATURES

Essentials of Diagnosis

• Most aortic aneurysms are asymptomatic until rupture

• 80% of abdominal aortic aneurysms measuring 5 cm are palpable; the usual threshold for treatment is 5.5 cm in men and 5 cm in women

• Back or abdominal pain with aneurysmal tenderness may precede rupture

• Rupture is catastrophic; excruciating abdominal pain that radiates to the back; hypotension

General Considerations

• The aorta of a healthy young man measures ∼2 cm

• An aneurysm is present when the aortic diameter > 3 cm

• Aneurysms rarely cause rupture until diameter > 5 cm

• 90% of abdominal atherosclerotic aneurysms originate below the renal arteries

• Aortic bifurcation is usually involved

• Common iliac arteries are often involved

Demographics

• Found in 2% of men > age 55

• Male to female ratio is 4:1

• Less common in patients with diabetes mellitus

CLINICAL FINDINGS

Symptoms and Signs

• Patients often have concomitant disease typically seen in older men who smoke cigarettes

  • Coronary artery disease

  • Carotid disease

  • Kidney disease

  • Emphysema

• 80% of 5-cm infrarenal aneurysms are palpable on routine physical examination

• Most asymptomatic aneurysms are discovered on ultrasound or CT imaging as part of a screening program or incidentally

• Most aneurysms have a thick layer of thrombus lining the aneurysmal sac, but embolization to the lower extremities occurs rarely

• Symptomatic aneurysms

  • Mild to severe midabdominal discomfort due to aneurysmal expansion often radiates to lower back

  • Pain may be constant or intermittent, exacerbated by even gentle pressure on aneurysm sack

  • Pain may also accompany inflammatory aneurysms

• Ruptured aneurysms

  • Severe pain

  • Hypotension

  • Free rupture into peritoneal cavity is lethal

DIAGNOSIS

Laboratory Tests

• Hematocrit may be normal since there has been no hemodilution in acute cases of a contained retroperitoneal rupture

Imaging Studies

• Abdominal ultrasonography

  • Diagnostic study of choice for initial screening

  • Screening guidelines

    • Recommend screening in men 65–75 years old with exposure to 100 or more lifetime cigarettes

    • Conflict on whether women with the same exposure should be screened

    • If the diameter of the aorta is 2–2.9 cm, repeat imaging in 10 years

    • While patients are monitored, smoking cessation and treatment of underlying hypertension, hyperlipidemia, and diabetes are recommended

• Abdominal or back radiographs: curvilinear calcifications outlining portions of aneurysm wall may be seen in ∼75% of patients

• CT scans

  • Provide a more reliable assessment of aneurysm diameter

  • Should be done when the aneurysm nears the diameter threshold (5.5 cm) for treatment

• Contrast-enhanced CT scans

  • Show the arteries above and below the aneurysm

  • Visualization of the visceral and renal vasculature is essential for planning repair

  • Often demonstrates mural thrombus within the aneurysm and is not an indication for anticoagulation