What does infrarenal (below the renal arteries) aneurysm refer to in vascular terms?

Infrarenal Abdominal Aortic Aneurysm: Definition and Clinical Significance

An infrarenal abdominal aortic aneurysm refers to a localized dilatation of the abdominal aorta below the renal arteries, with a diameter of 3 cm or greater, representing at least a 50% increase from the normal aortic diameter. 1

Anatomical Definition

• The normal dimension of the infrarenal abdominal aorta is up to 2 cm in anteroposterior diameter, and is considered aneurysmal when it reaches ≥3 cm in diameter 1
• Infrarenal refers specifically to the segment of the abdominal aorta that is located below (distal to) the renal arteries 2
• This is distinct from juxtarenal aneurysms (next to the origin of renal arteries but not involving them) and suprarenal aneurysms (extending above at least one renal artery) 3
• Infrarenal AAAs are the most common location for aortic aneurysms 4

Diagnostic Imaging

• Ultrasound is recommended as the first-line imaging modality for suspected infrarenal AAA, with highest appropriateness rating (9/9) 1
• CT angiography with IV contrast provides comprehensive evaluation of AAA with high appropriateness rating (8/9) 1
• MR angiography without and with IV contrast is also highly appropriate for evaluating AAA (8/9 rating) 1
• Imaging helps determine aneurysm size, involvement of abdominal branches, and extent of the aneurysm 1

Management Approach

• Surveillance is recommended for smaller aneurysms with intervals based on maximum diameter 2:

  • Every 6 months for 4.5 to 5.4 cm diameter
  • Every 12 months for 3.5 to 4.4 cm diameter
  • Every 3 years for 3.0 to 3.4 cm diameter
  • Every 5 years for 2.6 to 2.9 cm diameter

• Intervention is indicated for 2:

  • Infrarenal AAAs measuring 5.5 cm or larger in men
  • Infrarenal AAAs measuring 4.5-5.0 cm or larger in women
  • Symptomatic AAAs regardless of size
  • Rapidly expanding AAAs (growth >0.5 cm in 6 months)

Treatment Options

• Open surgical repair is indicated as the primary treatment for patients who are good or average surgical candidates 5
• Endovascular aneurysm repair (EVAR) is reasonable in patients at high risk of complications from open operations due to cardiopulmonary or other associated diseases 5
• EVAR may be considered in patients at low or average surgical risk, though long-term outcomes continue to be evaluated 5

Clinical Significance

• Abdominal aortic aneurysms are the 13th leading cause of death in the United States 4
• Most infrarenal AAAs are asymptomatic until rupture, which is often catastrophic 6
• The strongest predictor of AAA rupture is the diameter 7
• Population-based ultrasound screening has proven cost-effective for men >65 years of age, particularly those with risk factors including hypertension, smoking, and family history 1

Post-Intervention Management

• Periodic long-term surveillance imaging is mandatory after endovascular repair to monitor for complications 2
• Annual duplex ultrasound with additional cross-sectional imaging every 5 years is recommended for stable EVAR repairs 2
• The risk of late aortic rupture after EVAR remains >5% through 8 years, emphasizing the need for continued surveillance 2

Understanding the precise anatomical location of infrarenal AAAs is crucial for appropriate management decisions and surgical planning, particularly when considering endovascular approaches that require adequate neck length for graft fixation.