When should a patient with a diagnosed abdominal aortic aneurysm (AAA) and a history of smoking, hypertension, and atherosclerosis, typically over 65 years old, be referred to vascular surgery?

When to Refer AAA to Vascular Surgery

Refer a patient with abdominal aortic aneurysm to vascular surgery when the aneurysm reaches ≥5.5 cm in men or ≥5.0 cm in women, or when specific high-risk features develop regardless of size.

Size-Based Referral Thresholds

The primary indication for vascular surgery referral is based on maximum aneurysm diameter:

• Men: ≥5.5 cm diameter warrants elective repair referral 1, 2
• Women: ≥5.0 cm diameter requires referral, as women have a four-fold higher rupture risk than men at equivalent sizes 1, 2
• These thresholds represent the point where rupture risk exceeds operative mortality risk, with 1-year rupture rates of 9% for aneurysms 5.5-5.9 cm 1

Rapid Growth Requiring Urgent Referral

Refer immediately if the aneurysm expands ≥1.0 cm per year or ≥0.5 cm in 6 months, as rapid expansion indicates increased rupture risk independent of absolute size 1, 2, 3. Growth rates >2 mm per year are associated with increased adverse events and warrant closer surveillance with consideration for earlier intervention 4, 1.

High-Risk Morphologic Features

Refer for surgical evaluation when imaging reveals:

• Saccular morphology: This focal outpouching increases rupture risk even below the 5.5 cm threshold and may warrant earlier intervention 1, 2, 3
• Iliac artery aneurysm involvement: Concurrent iliac aneurysms are a documented indication for repair below standard diameter thresholds 3

Symptomatic AAA Requiring Emergency Referral

Any symptoms attributable to the aneurysm mandate urgent vascular surgery referral within 24-48 hours, regardless of size 2. Symptoms include:

• Abdominal, back, or flank pain suggesting impending rupture
• Distal embolization from mural thrombus 3
• Signs of aortic rupture (hypotension, pulsatile mass, severe pain)

Patient-Specific Factors Lowering Threshold

Consider earlier referral in:

• Younger, good-risk patients where the lifetime rupture risk may exceed operative risk even at smaller sizes 5
• Patients with family history of AAA rupture, as genetic factors may increase rupture risk 4
• Patients with uncontrolled resistant hypertension, which accelerates aneurysm growth 4, 1

Surveillance Protocol Before Referral

For aneurysms below surgical thresholds, maintain surveillance with:

• 4.5-5.4 cm: Ultrasound every 6 months 4, 1, 2
• 3.5-4.4 cm: Ultrasound every 12 months 1
• 3.0-3.4 cm: Ultrasound every 3 years 1

If ultrasound cannot adequately measure the aneurysm, obtain CT angiography to better characterize morphology and identify saccular features that may warrant earlier referral 1, 2.

Common Pitfalls to Avoid

Do not delay referral in women with 5.0 cm aneurysms thinking the 5.5 cm threshold applies universally—women rupture at smaller diameters with mean rupture diameter of 5.0 cm versus 6.0 cm in men 2.

Do not assume all sub-threshold repairs are inappropriate—approximately 60% of repairs below size recommendations are performed for legitimate indications including saccular morphology, rapid expansion, or iliac involvement 3. However, ensure these indications are clearly documented.

Ensure consistent measurement technique across surveillance studies, measuring perpendicular to the aortic centerline rather than in the axial plane, as tortuous aortas can lead to overestimation 4, 1.