Abdominal Aortic Aneurysm

 

• Focal widening >3 cm
• Normal size of abdominal aorta >50 years of age:
  • About 2 cm
• Prevalence:
  • Increases with age
  • Greater with atherosclerotic disease
  • Male predominance
  • Whites: Blacks = 3:1
• Risk factors:
  • male
  • age >75 years
  • white race
  • prior vascular disease
  • hypertension
  • cigarette smoking
  • family history
  • hypercholesterolemia
• Associated with:
  • visceral + renal artery aneurysm (2%)
  • isolated iliac + femoral artery aneurysm (16%)
    • common iliac (89%), internal iliac (10%), external iliac (1%)
  • stenosis / occlusion of celiac trunk / SMA (22%)
  • stenosis of renal artery (22-30%)
  • occlusion of inferior mesenteric artery (80%)
  • occlusion of lumbar arteries (78%)
• Growth rate of aneurysm of 3-6 cm in diameter:
  • 0.39 cm / year
• Clinical
  • asymptomatic (30%)
  • abdominal mass (26%)
  • abdominal pain (37%)
• Location
  • infrarenal (91-95%) with extension into iliac arteries (66-70%)
• Imaging findings
  • Plain film
    • mural calcification (75-86%)
  • US:>98% accuracy in size measurement
  • CT-non-contrast enhanced
    • perianeurysmal fibrosis (10%), may cause ureteral obstruction
    • "crescent sign" = peripheral high-attenuating crescent in aneurysm wall (= acute intramural hematoma) = sign of impending rupture
  • CT-contrast-enhanced
    • ruptured aneurysm
      • anterior displacement of kidney
      • extravasation of contrast material
      • fluid collection / hematoma within posterior pararenal + perirenal spaces (see below)

• free intraperitoneal fluid
• contained leak
  • laminated mural calcification
  • periaortic mass of mixed / soft-tissue density
  • lateral "draping" of aneurysm around vertebral body
• Angio
  • focally widened aortic lumen >3 cm
  • apparent normal size of lumen secondary to mural thrombus (11%)
  • mural clot (80%)
  • slow antegrade flow of contrast medium
• Contained rupture = extraluminal hematoma / cavity
  • absent parenchymal stain = avascular halo
  • displacement + stretching of aortic branches
• Complications:
  • Rupture (25%)
    • into retroperitoneum: commonly on left
    • into GI tract: massive GI hemorrhage
    • into IVC: rapid cardiac decompensation
      • Incidence: aneurysm <4 cm in 10%, 4-5 cm in 23%, 5-7 cm in 25%, 7-10 cm in 46%, >10 cm in 60%
      • Symptoms of rupture
        • sudden severe abdominal pain ± radiating into back
        • faintness, syncope, hypotension
        • Prognosis:64-94% die before reaching hospital
        • Increased risk: size >6 cm, growth >5 mm / 6 months, pain + tenderness
  •  Peripheral embolization
  • Infection
  • Spontaneous occlusion of aorta
• Prognosis:17% 5-year survival without surgery
  • 50-60% 5-year survival with surgery
• Treatment
  • surgery recommended if >5 cm in diameter;
  • 4-5% surgical mortality for nonruptured
    • 30-80% for ruptured aneurysm
• Postoperative Complications
  • Left colonic ischemia (1.6%) with 10% mortality
  • Renal failure (14%)
  • 0-8% mortality rate for elective surgery

 

From Dahnert Radiology Review Manual 2002