What abdominal aortic aneurysm diameter warrants immediate surgical repair in adults (≥5.5 cm in men, ≥5.0 cm in women or connective‑tissue disease, or growth ≥0.5 cm in 6 months)?

Abdominal Aortic Aneurysm: Size Thresholds for Immediate Surgical Repair

Immediate surgical repair is indicated for AAAs ≥5.5 cm in men, ≥5.0 cm in women, or any AAA with rapid growth ≥0.5 cm in 6 months or ≥1.0 cm per year, regardless of absolute diameter. 1, 2

Size-Based Intervention Thresholds

Standard Diameter Criteria

• Men: ≥5.5 cm represents the threshold where annual rupture risk (approximately 9-10%) exceeds the operative mortality of elective repair (approximately 4%), making intervention beneficial. 1, 2

• Women: ≥5.0 cm is the appropriate threshold because women experience a four-fold higher rupture risk at equivalent diameters compared to men, with mean rupture diameter of 5.0 cm versus 6.0 cm in men. 1, 2

• These thresholds are supported by multiple randomized controlled trials (UKSAT, ADAM, CAESAR, PIVOTAL) demonstrating no survival benefit from earlier repair at smaller sizes. 2, 3, 4

Growth Rate Criteria (Independent of Absolute Size)

• ≥1.0 cm per year: Mandates immediate repair at any diameter (Class I evidence). 1, 2

• ≥0.5 cm in 6 months: Warrants strong consideration for repair, as this rapid expansion signals heightened rupture risk independent of absolute diameter. 1, 2

• Growth rates >2 mm per year are associated with increased adverse events and should prompt closer surveillance with lower threshold for intervention. 1

Absolute Indications for Immediate Repair (Regardless of Size)

Symptomatic AAA

• Any AAA presenting with abdominal, back, or flank pain attributable to the aneurysm requires immediate repair regardless of diameter, as symptoms indicate impending rupture. 1, 2

• Patients with symptomatic AAAs should be admitted to an ICU for arterial blood pressure monitoring, tight blood pressure control, and AAA repair ideally within 24-48 hours to reduce risk of free rupture. 1

• Symptomatic AAAs have significantly higher mortality and morbidity rates than elective repairs, with 25% of symptomatic saccular AAAs presenting at diameters <5.5 cm. 1

Saccular Morphology

• Saccular AAAs warrant elective repair at smaller diameters than fusiform aneurysms because they rupture more readily (Class IIb, Level C-LD evidence). 1, 2

• In a Dutch registry, 25% of saccular AAAs presenting acutely had diameters <5.5 cm, compared to only 8.1% of fusiform AAAs. 1

• Consider intervention for saccular AAAs ≥4.5 cm in diameter. 2

Additional High-Risk Features

• Distal embolization (blue toe syndrome) indicates need for urgent repair. 1, 2

• Compressive symptoms (obstructive uropathy) warrant expedited repair. 1

• Tenderness to palpation overlying the AAA in the abdomen, back, or flank requires expedited evaluation. 1

Rupture Risk Stratification by Size

Understanding rupture risk helps contextualize the urgency of intervention:

• <5.0 cm: Annual rupture risk 0.5-5% 2
• 5.0-5.4 cm: Annual rupture risk 3-15% 2
• 5.5-5.9 cm: Annual rupture risk approximately 9% 1, 2
• 6.0-6.9 cm: Annual rupture risk approximately 10% 1, 2
• ≥7.0 cm: Annual rupture risk approximately 33% 1, 2

The mortality rate of ruptured AAA is 75-90%, with more than half of deaths occurring before hospital arrival. 2, 5

Common Pitfalls to Avoid

• Do not apply the same diameter thresholds to men and women—women require intervention at 5.0 cm, not 5.5 cm, due to sex-specific rupture risk differences. 1, 2

• Do not delay repair for "optimization" in patients meeting size criteria—the rupture risk at threshold diameters already exceeds operative mortality. 2

• Do not assume asymptomatic status without explicitly asking about pain—symptomatic AAAs require immediate repair regardless of size. 1, 2

• Do not ignore rapid growth rates—expansion ≥0.5 cm in 6 months warrants intervention even if absolute diameter is below standard thresholds. 1, 2

• Do not overlook saccular morphology—these aneurysms rupture at smaller sizes than fusiform aneurysms and require earlier intervention. 1, 2

Surveillance Protocol for Sub-Threshold AAAs

For AAAs that do not meet immediate repair criteria:

• 3.0-3.9 cm: Imaging every 2-3 years with duplex ultrasound 2, 6
• 4.0-4.4 cm: Imaging every 12 months with duplex ultrasound 2, 6
• 4.5-5.4 cm (men) or 4.5-5.0 cm (women): Imaging every 6 months with duplex ultrasound 1, 2, 6

Duplex ultrasound is the preferred surveillance modality due to lack of radiation, lower cost, and comparable accuracy to CT, though it may underestimate diameter by approximately 4 mm. 1, 2, 6

Contraindications to Repair

• Do not repair AAAs in patients with life expectancy <2 years (Class III, Level B evidence), as the operative risk exceeds potential benefit. 2