Surgery for small abdominal aortic aneurysms that do not cause symptoms

An aneurysm is a ballooning of an artery (blood vessel), which, in the case of an abdominal aortic aneurysm (AAA), occurs in the major artery in the abdomen (aorta). Ruptured AAAs cause death unless surgical repair is rapid, which is difficult to achieve. Surgery is considered necessary for people with aneurysms of more than 5.5 cm in diameter or who have associated pain, to relieve symptoms and to reduce the risk of rupture and death. However, risks are associated with surgery. Surgical repair consists of insertion of a prosthetic inlay graft, either by open surgery or endovascular repair.

Small asymptomatic AAAs are at low risk of rupture and are monitored through regular imaging so they can be surgically repaired if they subsequently enlarge. This review identified four well-conducted, controlled trials that randomised 3314 participants with small (diameter 4.0 cm to 5.5 cm) asymptomatic AAAs to immediate repair or regular, routine ultrasounds to check for aneurysm growth (surveillance). Among the patients randomised to surveillance, the aneurysm was repaired if it was enlarging, reached 5.5 cm in diameter, or became symptomatic. The four trials showed an early survival benefit in the surveillance group because of the number of deaths within 30 days of surgery (operative mortality). The trials did not show a meaningful difference in long-term survival between immediate repair and selective surveillance over the three to eight years of follow-up. Some 31% to 75% of the participants randomised to surveillance eventually had the aneurysm repaired. Overall, the risk of bias within the included studies was low and the quality of the evidence high. The results from the four trials conducted to date suggest no overall advantage to immediate surgery for small AAAs (4.0 cm to 5.5 cm). A pooled analysis of the two trials comparing immediate open surgical repair to surveillance demonstrated that this result holds true regardless of patient age or aneurysm size (within the range of 4.0 cm to 5.5 cm diameter). Furthermore, the more recent trials, which focused on the efficacy of endovascular repair, also failed to show a benefit over surveillance. Quality-of-life results among trials were conflicting. Thus, neither immediate open nor immediate endovascular repair of small AAAs is supported by the current evidence.

Authors' conclusions: 

The results from the four trials to date demonstrate no advantage to immediate repair for small AAA (4.0 cm to 5.5 cm), regardless of whether open or endovascular repair is used and, at least for open repair, regardless of patient age and AAA diameter. Thus, neither immediate open nor immediate endovascular repair of small AAAs is supported by currently available evidence.

Read the full abstract...

An abdominal aortic aneurysm (AAA) is an abnormal ballooning of the major abdominal artery. Some AAAs present as emergencies and require surgery; others remain asymptomatic. Treatment of asymptomatic AAAs depends on many factors, but an important one is the size of the aneurysm, as risk of rupture increases with aneurysm size. Large asymptomatic AAAs (greater than 5.5 cm in diameter) are usually repaired surgically; very small AAAs (less than 4.0 cm diameter) are monitored with ultrasonography. Debate continues over the appropriate roles of immediate repair and surveillance with repair on subsequent enlargement in people presenting with asymptomatic AAAs of 4.0 cm to 5.5 cm diameter. This is the third update of the review first published in 1999.


To compare mortality, quality of life, and cost effectiveness of immediate surgical repair versus routine ultrasound surveillance in people with asymptomatic AAAs between 4.0 cm and 5.5 cm in diameter.

Search strategy: 

For this update, the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (February 2014) and the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 1). We checked reference lists of relevant articles for additional studies.

Selection criteria: 

Randomised controlled trials in which men and women with asymptomatic AAAs of diameter 4.0 cm to 5.5 cm were randomly allocated to immediate repair or imaging-based surveillance at least every six months. Outcomes had to include mortality or survival.

Data collection and analysis: 

Three members of the review team independently extracted the data, which were cross-checked by other team members. Risk ratios (RR) (endovascular aneurysm repair only), hazard ratios (HR) (open repair only), and 95% confidence intervals based on Mantel-Haenszel Chi2 statistic were estimated at one and six years (open repair only) following randomisation. We included all relevant published studies in this review.

Main results: 

For this update, four trials with a combined total of 3314 participants fulfilled the inclusion criteria. Two trials compared surveillance with immediate open repair; two trials compared surveillance with immediate endovascular repair. Overall, the risk of bias within the included studies was low and the quality of the evidence high. The four trials showed an early survival benefit in the surveillance group (due to 30-day operative mortality with surgery) but no significant differences in long-term survival (adjusted HR 0.88, 95% confidence interval (CI) 0.75 to 1.02, mean follow-up 10 years; HR 1.21, 95% CI 0.95 to 1.54, mean follow-up 4.9 years; HR 0.76, 95% CI 0.30 to 1.93, median follow-up 32.4 months; HR 1.01, 95% CI 0.49 to 2.07, mean follow-up 20 months). A pooled analysis of participant-level data from two trials (with a maximum follow-up of seven to eight years) showed no statistically significant difference in survival between immediate open repair and surveillance (propensity score-adjusted HR 0.99; 95% CI 0.83 to 1.18), and that this lack of treatment effect did not vary by AAA diameter (P = 0.39) or participant age (P = 0.61). The meta-analysis of mortality at one year for the endovascular trials likewise showed no significant association (RR at one year 1.15, 95% CI 0.60 to 2.17). Quality-of-life results among trials were conflicting.