Objectives: Apart from aortic diameter, two other widely used criteria for considering surgery in screen-detected abdominal aortic aneurysms (AAAs) - annual aortic expansion ≥1.0 cm and presence of symptoms attributable to the AAA 0 are based on accepted practice and AAA expansion rates, rather than direct evidence. The Multi-centre Aneurysm Screening Study (MASS) enables assessment of their contribution to this risk reduction.
Methods: MASS employs three criteria for referral for considering elective open surgery: maximum aortic diameter ≥5.5 cm, rapid aortic expansion (≥1.0 cm/year), and/or the presence of symptoms attributable to the AAA. Data from MASS are used to examine the value of these criteria in practice.
Results: No patients were referred for symptoms alone. Of those referred for rapid expansion, 88% were returned to surveillance, compared with only 12% of those referred for diameter ≥5.5 cm at initial scan, and 34% of those referred for diameter ≥5.5 cm at a follow-up scan. Return to surveillance following referral for rapid expansion was strongly associated with aortic diameter (age-adjusted odds ratio for return 0.89 per mm, 95% confidence interval 0.79-1.00). Of those 5.0-5.4 cm at the time of referral for rapid expansion who were returned, 31% reached 5.5 cm during a median post-referral follow-up of 0.9 years. Among those referred for expansion, the rupture rate was only 8 per 1000 person-years of follow-up prior to reaching 5.5 cm.
Conclusions: A single criterion for considering elective surgery is recommended in screen-detected AAA, based on a maximum aortic diameter of ≥5.5 cm. This criterion detects the majority of those at risk from rupture, and is simple to assess.
