C. G. Collins
A. L. Leahy
Department of Vascular Surgery,
Royal College of Surgeons in Ireland and Beaumont Hospital, Dublin 9, Ireland

Correspondence to: A. Leahy
Department of Vascular Surgery,
Royal College of Surgeons in Ireland and Beaumont Hospital, Dublin 9, Ireland
Email: dquinn@rcsi.ie

Keywords: Abdominal aortic aneurysm, screening, cost-effectiveness
Surgeon, 1 April 2006 83-85

INTRODUCTION
It would seem timely to review the evidence for and against screening of abdominal aortic aneurysms (AAAs). The incidence of AAAs in Britain and Ireland has increased in the last two decades.1 This is due in part to the ageing population, the rising number of smokers and possibly due to improved detection.1 Despite surgical advances, the overall mortality for ruptured AAAs remains between 65% and 85%, with half of these deaths occurring prior to undergoing surgery.2 Elective aneurysm repair has a reported mean 30-day mortality of 2% to 6%.3,4
Abdominal aortic aneurysms are found in 4% to 8% of older men, with age, smoking and family history being the most potent risk factors.5,6 They would appear to be suitable for screening as they are common in older men, have a long asymptomatic phase of development, are accurately detected by ultrasound, and treatment prior to rupture improves survival. Ultrasonography is a useful and accurate screening tool with a sensitivity of 98.9% and a specificity of 99.9%. AAA screening by ultrasound assessment fulfils all the WHO criteria for screening.7,8

EFFECTIVENESS OF DETECTION
In 1996 the United States Preventative Services Task Force (USPSTF) found insufficient evidence to support routine screening for AAAs, citing the need for population-based screening trials.9 These trials have since been completed and the USPSTF has now recommended abdominal aortic screening for men aged 65 to 75 years.6 The Aneurysm Detection and Management (ADAM) and the United Kingdom small aneurysm trial have shown us that small aneurysms (less that 55mm in diameter) can be safely monitored before considering elective surgery10,11 Population-based screening trials such as the Multicentre Aneurysm Screening Study (MASS) trial have shown that aneurysm screening can reduce mortality due to AAA by 42%, compared with controls (37% vs 6%) in men aged 65 to 74.3 Screening for AAAs in women has not shown a mortality benefit because of the lower incidence in this population. However with the number of female smokers on the increase this deserves further study.12 A population screening programme in Gloucestershire carried out ultrasound scanning for all men at age 65 years. If the aorta was less than 26mm in diameter they were reassured and discharged, as aneurysm disease can be ruled out for 95% of these patients.13 If the aorta was between 26mm and 39mm in diameter, the patient was referred for annual scanning, while an aorta greater than 40mm required a vascular surgical referral with close surveillance. Elective repair was considered if it was above 55mm. Following the introduction of this programme, the total number of aneurysm-related deaths in this population decreased significantly year by year. However in this population 15% of men failed to attend screening and 10% of aneurysms had ruptured before the age of 65.

MEDICAL BENEFIT
BEST MEDICAL THERAPY
The primary aim in AAA management is the prevention of rupture. The secondary aim is prevention of aneurysm expansion. Patients with an AAA who stop smoking tobacco completely have a reduction in the growth rate of the aneurysm.14
The role of matrix metalloproteinases (MMPs), which degrade elastin and collagen fibres, in the development of AAAs has been confirmed in animal models.15,16 Tetracyclines provide a potentially effective treatment, with doxycycline shown to prevent MMP-medicated expansion in animals and humans.17,18 Non-steroidal anti-inflammatory drugs are also known to prevent development of AAAs in animal models.19 The use of β-blocking agents clinically appear to reduce the growth rate of large (>5cm) aneurysms and even to lessen the size of experimental aneurysms. However they have not been shown to have any effect on small aneurysms.20 Statins reduce the expression of various inflammatory molecules including MMPs, which suggest that they could have an effect in reducing the expansion of AAAs. Early detection of small AAAs by screening can potentially allow best medical therapy to limit aneurysm development and reduce the need for surgical intervention.

PSYCHOLOGICAL EFFECTS
Some authors have mentioned the potential deleterious psychological effects of informing patients about the presence of a small aneurysm for which regular monitoring is required.21 On the basis of the MASS trial observations, while there was initially more anxiety in the patients who had a positive scan (evidenced by lower Short Form 36 mental and physical scores) these differences were no longer apparent after six weeks.3

COST-EFFECTIVENESS
In order for population screening to be adopted on a national basis it has to be economically viable. The cost-effectiveness of screening for AAAs was assessed by the MASS trial. This found that the mean additional cost of the screening programme was £63.39 per patient, with the cost-effective ratio amounting to £36,000 per quality adjusted life year, falling to £8,000 per life year gained after ten years, with 710 patients being screened to prevent one death. This is a reasonable cost.

IMPACT OF ENDOVASCULAR REPAIR
The advent of endovascular repair, with a lower operative mortality rate and less frequent post-operative complications than open aneurysm surgery, may also be used as an argument to extend indications for surgical intervention.22 Long-term results after endovascular repair have also been reported to be better for smaller aneurysms, which may further favour treatment of screen-detected AAAs.23
The past 50 years have been marked by continuing progress in diagnosis, management, timing of intervention and optimisation of surgery in the treatment of AAAs. It is now clear that a single ultrasound scan at age 65 is a cost-effective screening strategy for AAAs and with improvements in medical and surgical treatments it would seem to be advisable.

Copyright 13 October 2005

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