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 recommended for people with aneurysms bigger than 5.5 cm in diameter or who have associated pain, to relieve symptoms and reduce the risk of rupture and death. However, there are risks with surgery. Surgical repair consists of re-lining the aorta with strong synthetic material, either by open surgery or endovascular repair (a minimally invasive keyhole procedure). Small asymptomatic (no symptoms) AAAs are at low risk of rupture and are monitored through regular imaging so they can be surgically repaired if they grow.

Key results

We found four well-conducted trials that randomised 3314 participants with small (diameter 4.0 cm to 5.5 cm) asymptomatic AAAs to early repair or regular, routine ultrasounds to check for aneurysm growth (surveillance) (search current to 10 July 2019). In the surveillance group, the aneurysm was repaired if it was enlarging, reached 5.5 cm in diameter, or became symptomatic. The 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 found no difference in long-term survival between early repair (open or endovascular) and surveillance over three to eight years of follow-up. After three years, about 31% of the participants randomised to surveillance eventually had the aneurysm repaired, rising to 75% after 12 years.

Two trials reported costs. For the first 18 months, costs were lower with surveillance than either open repair or endovascular repair. After four years, one trial found similar total medical costs for early endovascular repair and surveillance groups. After 12 years, another trial found lower hospital costs with surveillance than with open repair.

The four studies used different ways to measure quality of life and results were conflicting. The percentage of aneurysm ruptures in the surveillance group appeared higher in the trials using open repair but these have not restricted participants to those with aortic anatomy suitable for endovascular repair. Most ruptures were in people whose previous aneurysm diameter exceeded the threshold for surgical repair.

Reliability of the evidence

The methods within the studies using open repair were good and the reliability of the evidence was high to moderate for the two trials comparing open repair with surveillance. For the two trials comparing endovascular repair with surveillance, the risk of bias was unclear to high and the reliability of the evidence was low. The four trials suggest no overall advantage with early surgery for small AAAs (4.0 cm to 5.5 cm). The two trials comparing early open surgical repair to surveillance found 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 two trials that focused on endovascular repair, also found no benefit over surveillance. Neither early open nor early endovascular repair of small AAAs is supported by the current evidence.

Authors' conclusions: 

There was no evidence of an advantage to early repair for small AAA (4.0 cm to 5.5 cm), regardless of whether open repair or EVAR is used and, at least for open repair, regardless of patient age and AAA diameter. Thus, neither early open nor early EVAR of small AAAs is supported by currently available evidence. Long-term data from the two trials investigating EVAR are not available, so, we can only draw firm conclusions regarding outcomes after the first few years for open repair. Research regarding the risks related to and management of small AAAs in ethnic minorities and women is urgently needed, as data regarding these populations are lacking.

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 the size of the aneurysm is important, 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 roles of early repair versus surveillance with repair on subsequent enlargement in people with asymptomatic AAAs of 4.0 cm to 5.5 cm diameter. This is the fourth update of the review first published in 1999.


To compare mortality and costs, as well as quality of life and aneurysm rupture as secondary outcomes, following early surgical repair versus routine ultrasound surveillance in people with asymptomatic AAAs between 4.0 cm and 5.5 cm in diameter.

Search strategy: 

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, two other databases, and two trials registers to 10 July 2019. We handsearched conference proceedings and checked reference lists of relevant studies.

Selection criteria: 

We included randomised controlled trials where people with asymptomatic AAAs of 4.0 cm to 5.5 cm were randomly allocated to early repair or imaging-based surveillance at least every six months. Outcomes had to include mortality or survival.

Data collection and analysis: 

Three review authors independently extracted data, which were cross-checked by other team members. Outcomes were mortality, costs, quality of life, and aneurysm rupture. For mortality, we estimated risk ratios (RR) (endovascular aneurysm repair only), hazard ratios (HR) (open repair only), and 95% confidence intervals (CI) based on Mantel-Haenszel Chi2 statistics at one and six years (open repair only) following randomisation.

Main results: 

We found no new studies for this update. Four trials with 3314 participants fulfilled the inclusion criteria. Two trials compared early open repair with surveillance and two trials compared early endovascular repair (EVAR) with surveillance. We used GRADE to access the certainty of the evidence for mortality and cost, which ranged from high to low. We downgraded the certainty in the evidence from high to moderate and low due to risk of bias concerns and imprecision (some outcomes were only reported by one study).

All four trials showed an early survival benefit in the surveillance group (due to 30-day operative mortality with repair) but no evidence of differences in long-term survival. One study compared early open repair with surveillance with an adjusted HR of 0.88 (95% 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). Pooled analysis of participant-level data from the two trials comparing early open repair with surveillance (maximum follow-up seven to eight years) showed no evidence of a difference in survival (propensity score-adjusted HR 0.99, 95% CI 0.83 to 1.18; 2226 participants; high-certainty evidence). This lack of treatment effect did not vary to three years by AAA diameter (P = 0.39), participant age (P = 0.61), or for women (HR 0.84, 95% CI 0.62 to 1.11). Two studies compared EVAR with surveillance and there was no evidence of a survival benefit for early EVAR at 12 months (RR 1.92, 95% CI 0.73 to 5.06; 846 participants; low-certainty evidence).

Two trials reported costs. The mean UK health service costs per participant over the first 18 months after randomisation were higher in the open repair surgery than the surveillance group (GBP 4978 in the repair group versus GBP 3914 in the surveillance group; mean difference (MD) GBP 1064, 95% CI 796 to 1332; 1090 participants; moderate-certainty evidence). There was a similar difference after 12 years. The mean USA hospital costs for participants at six months after randomisation were higher in the EVAR group than in the surveillance group (USD 33,471 with repair versus USD 5520 with surveillance; MD USD 27,951, 95% CI 25,156 to 30,746; 614 participants; low-certainty evidence). After four years, there was no evidence of a difference in total medical costs between groups (USD 48,669 with repair versus USD 46,112 with surveillance; MD USD 2557, 95% CI –8043 to 13,156; 614 participants; low-certainty evidence).

All studies reported quality of life but used different assessment measurements and results were conflicting.

All four studies reported aneurysm rupture. There were very few ruptures reported in the trials of EVAR versus surveillance up to three years. In the trials of open surgery versus surveillance, there were ruptures to at least six years and there were more ruptures in the surveillance group, but most of these ruptures occurred in aneurysms that had exceeded the threshold for surgical repair.