Elsevier

The Lancet

Volume 360, Issue 9345, 16 November 2002, Pages 1531-1539
The Lancet

Articles
The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial

https://doi.org/10.1016/S0140-6736(02)11522-4Get rights and content

Summary

Background

Opposing views have been published on the importance of ultrasound screening for abdominal aortic aneurysms. The Multicentre Aneurysm Screening Study was designed to assess whether or not such screening is beneficial.

Methods

A population-based sample of men (n=67 800) aged 65–74 years was enrolled, and each individual randomly allocated to either receive an invitation for an abdominal ultrasound scan (invited group, n=33 839) or not (control group, n=33 961). Men in whom abdominal aortic aneurysms (⩾3 cm in diameter) were detected were followed-up with repeat ultrasound scans for a mean of 4·1 years. Surgery was considered on specific criteria (diameter ⩾5·5 cm, expansion ⩾1 cm per year, symptoms). Mortality data were obtained from the Office of National Statistics, and an intention-to-treat analysis was based on cause of death. Quality of life was assessed with four standardised scales. The primary outcome measure was mortality related to abdominal aortic aneurysm.

Findings

27 147 of 33 839 (80%) men in the invited group accepted the invitation to screening, and 1333 aneurysms were detected. There were 65 aneurysm-related deaths (absolute risk 0·19%) in the invited group, and 113 (0·33%) in the control group (risk reduction 42%, 95% CI 22–58; p=0·0002), with a 53% reduction (95% CI 30–64) in those who attended screening. 30-day mortality was 6% (24 of 414) after elective surgery for an aneurysm, and 37% (30 of 81) after emergency surgery.

Interpretation

Our results provide reliable evidence of benefit from screening for abdominal aortic aneurysms.

Introduction

Rupture of abdominal aortic aneurysms caused about 6800 deaths in England and Wales in the year 2000. Most of these deaths occurred in men—the age-specific prevalence of the condition being six times greater in men than in women.1 In men older than 65 years, ruptured abdominal aortic aneurysms are responsible for 2·1% of all deaths. Of the deaths attributed to ruptured aneurysms, about half take place before the patient reaches hospital.2, 3 For patients who reach hospital alive, the mortality rate for emergency treatment is 30–70%.3, 4 The overall mortality rate is, therefore, between 65% and 85%.4

Ultrasound can reliably visualise the aorta in 99% of people,5 thus providing the possibility of detection of an abdominal aortic aneurysm at a size when rupture is unlikely to occur. Intervention at this stage could reduce the frequency of rupture, and so reduce mortality and the requirement for emergency hospital treatment. Elective surgery for an abdominal aortic aneurysm is, however, also associated with a mortality risk of about 2–6%.3, 6, 7 Opposing views have, hence, been published on the potential importance of ultrasound screening for this condition.8, 9 Since ultrasound as a screening test is reasonably cheap and non-invasive, and the condition is a substantial cause of mortality, a randomised trial of sufficient size to detect realistic levels of effect was indicated.

Results of a pilot study indicated the feasibility of population screening by ultrasound, with participation rates of 68%.10 The findings of the pilot study also suggested that a reduction of 30% in mortality from ruptured abdominal aortic aneurysms, on an intention-to-treat basis, would be a realistic basis for power calculations. Accordingly, plans for such a trial, the Multicentre Aneurysm Screening Study (MASS), were drawn up in 1995–96. Investigators acknowledged at the outset that no trial of realistic size could have appreciable power to detect an effect on total mortality. MASS was therefore designed to have acceptable power for detecting a 30% reduction in mortality from ruptured aneurysms. The investigators were aware when designing the trial that similar, although smaller, trials were being planned in Denmark5 and Australia.7 An additional combined analysis of the three trials was suggested as part of the study protocol.

As well as showing clinical benefits, screening has to be shown not to adversely affect quality of life among participants. Results of previous studies of the psychological effect of screening for abdominal aortic aneurysms show no significant effects of detecting the condition on mood,11, 12 but do indicate some impairment of quality of life, especially in those who do not undergo surgical repair of aneurysms.13, 14 The validity of these conclusions is, however, limited by small sample sizes in many of the studies. There is also uncertainty about the cost-effectiveness of screening.9, 15

Here, we report the initial results from MASS on mortality, and the effect of screening on quality of life. A trial-based analysis of cost-effectiveness is being published elsewhere.16

Section snippets

Participants

Between January, 1997, and May, 1999, men aged 65–74 years from four centres (Portsmouth, Southampton, Winchester, and Oxford) in the UK were identified from family doctor lists and Health Authority lists, after obtaining the family doctor's permission. Before randomisation, doctors were asked to list patients they considered unfit to be screened. These were then excluded from the study. The study itself imposed no exclusion criteria other than sex and year of birth, but doctors typically

Results

Figure 1 shows the trial profile. 67 800 of 70 495 men considered for inclusion were randomised. The largest group excluded before randomisation were those whom family doctors considered unfit for screening (figure 1; other health reasons and other reasons not specified). One practice withdrew from the trial shortly after being included in the randomisation. The randomised groups were balanced at baseline in terms of screening centre (Portsmouth 33%, Southampton 28%, Oxford 26%, Winchester

Discussion

Our findings indicate that screening can significantly reduce mortality rates associated with abdominal aortic aneurysms, and show similar reductions in mortality rates to those reported from smaller randomised trials done in Chichester in the UK,10 and Denmark,24 and from two non-randomised population screening programmes in Huntingdon3 and Gloucester, UK.25 There was a similar aneurysm-related mortality among those in the invited group who did not attend for screening and those in the control

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