Regular Article
The Incidence of Small Abdominal Aortic Aneurysms and the Change in Normal Infrarenal Aortic Diameter: Implications for Screening

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Abstract

Aim: to study the incidence of small abdominal aortic aneurysms (AAA), and to investigate what proportion of normal infrarenal aortic diameters (IAD) expand with age. Methods: longitudinal follow-up in a population-based aneurysm screening programme. The infrarenal aortic diameter (IAD) was measured by ultrasound. A second scan was performed in subjects with a normal aorta after an average of 5.5 years. Results: data were analysed from 4072 subjects, 464 with a small AAA and 3608 with a normal aorta. The infrarenal aorta expanded in 15% of subjects, but significant growth (>5 mm) occurred in only 7%. Age and initial diameter were independent predictors for aortic dilatation. The effect of diameter at first screen was non-linear. The relative risk for expansion increased dramatically for IADs over 2.5 cm (test for departure of trend: χ2=52, p<0.0001). The effect of age was also non-linear, the risk of expansion was highest in the 60–69 year old age group; test for departure of trend (χ2=13,p =0.002). The incidence of new aneurysms was 3.5 per 1000 person-years (py) (95% CI: 2.8–4.4). The highest incidence of new aneurysms was found in the 60 to 69 year old age group. Conclusion: only a small proportion of the population is prone to aortic dilatation. Patients over 70 with an IAD <2.5 cm can be discharged from follow-up.

Keywords

Change in normal aortic diameter
Incidence of asymptomatic aneurysms.

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Presented at the XIVth Annual ESVS Meeting, London, 2000.

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Please address all correspondence to: A. B. M. Wilmink, Department of Vascular Surgery, Norfolk & Norwich Hospital, Brunswick Road, Norwich NR1 3SR, U.K.