Ultrasound surveillance of ectatic abdominal aortas

Some studies have considered abdominal aortas of 2.6-2.9 cm diameter (ectatic aortas) at age 65 years as being abnormal and have recommended surveillance, whereas others have considered these normal and surveillance unnecessary. It is, therefore, not clear how to manage patients with an initial aortic diameter between 2.6-2.9 cm detected at screening. The aim of this study was to evaluate growth rates of ectatic aortas detected on initial ultrasound screening to determine if any developed into clinically significant abdominal aortic aneurysms (AAAs; > 5.0 cm) and clarify the appropriate surveillance intervals for these patients.

Data were obtained from a prospective AAA screening programme which commenced in 1992. The group of patients with initial aortic diameters of 2.6-2.9 cm with a minimum of 1-year follow-up were included in this study (Group 2). This was further divided into two subgroups (Groups 3a and 3b) based on a minimum follow-up interval obtained from outcome analysis. Mean growth rate was calculated as change in aortic diameter with time. The comparison of growth rates in Groups 3a and 3b was performed using the t-test. The number and proportion of AAAs that expanded to >or= 3.0 cm and >or= 5.0 cm in diameter were also calculated.

Out of 999 patients with AAA >or= 2.6 cm with minimum 1-year follow-up, 358 (36%) were classified as ectatic aortas (2.6-2.9 cm) at initial ultrasound screening with the mean growth rate of 1.69 mm/year (95% CI, 1.56-1.82 mm/year) with a mean follow-up of 5.4 years. Of these 358 ectatic aortas, 314 (88%) expanded into >or= 3.0 cm, 45 (13%) expanded to >or= 5.0 cm and only 8 (2%) expanded to >or= 5.5 cm over a mean follow-up of 5.4 years (range, 1-14 years). No ectatic aortas expanded to >or= 5.0 cm within the first 4 years of surveillance. Therefore, the minimum follow-up interval was set at 4 years and this threshold was then used for further analysis. The mean growth rate in Group 3a (< 5.0 cm at last scan) was 1.33 mm/year (95% CI, 1.23-1.44 mm/year) with a mean follow-up of 7 years compared to Group 3b (>or= 5.0 cm at last scan) with the mean growth rate of 3.33 mm/year (95% CI 3.05-3.61 mm/year) and a mean follow-up of 8 years. The comparison of mean growth rates between Groups 3a and 3b is statistically significant (t-test; T = 13.00; P < 0.001).

One-third of patients undergoing AAA screening will have ectatic aortas (2.6-2.9 cm) and at least 13% of these will expand to a size of >or= 5.0 cm over a follow-up of 4-14 years. A threshold diameter of 2.6 cm for defining AAAs in a screening programme is recommended and ectatic aortas detected at age 65 years can be re-screened at 4 years after the initial scan. A statistically significant difference was found in the growth rates of ectatic aortas with minimum 4 years follow-up, expanding to >or= 5.0 cm compared to those less than 5.0 cm at last surveillance scan. Further studies are required to test the hypothesis of whether growth rate over the first 4 years of surveillance will identify those who are most likely to expand to a clinically significant size (> 5.0 cm).