Measuring abdominal aortic diameters in routine abdominal computed tomography scans and implications for abdominal aortic aneurysm screening.

OBJECTIVE: This study aimed to determine the prevalence and relevance of incidental abdominal aortic aneurysm (AAA) on routine abdominal computed tomography (CT) and to audit the performance of radiologists to identify and report AAA. METHODS: A retrospective audit of all abdominal CT scans performed on men and women ≥50 years at Dunedin Public Hospital between January 2013 and September 2014 was carried out. All CT scans for planning of AAA treatment or follow-up were excluded. The maximal anterior-posterior diameter of the infrarenal abdominal aorta was measured in both the sagittal and transverse planes on the picture archiving and communication system. The radiologist reports were analyzed. All detected AAAs were reviewed for clinical relevance. RESULTS: A total of 3332 scans were performed, of which 86 scans were excluded, resulting in a total cohort of 3246. There were 187 incidental AAAs detected with a prevalence of 5.8%. The prevalence was 8.7% in men and 3.1% in women. Whereas the prevalence increased with age, a significant number were detected in those younger than 65 years, with a prevalence of 1.5%. Of the 187 AAAs, 122 (65%) were reported by radiologists: 100% reporting rate in AAAs ≥50 mm, 87% in AAAs ≥40 to 49 mm, and 52% in AAAs ≥30 to 39 mm. Of these, 15% were specifically recommended for referral to a vascular service. Of the incidentally detected AAAs, 72% were considered to be clinically relevant, which is an overall 4.1% prevalence of AAAs with an ability to benefit. In addition, all 3246 subjects avoided the need for further AAA screening. CONCLUSIONS: There is a high prevalence of AAAs (5.8%) and clinically relevant AAAs (4.1%) detected on routine abdominal CT. As an opportunistic approach, it is a simple and effective way to detect AAAs and to broaden traditional screening criteria to include women and those younger than 65 years in our region. Furthermore, large numbers of subjects with normal aortic diameters are identified who will not need to be screened. Consequently, we consider routine diagnostic abdominal CT to be an important adjunct to national and community AAA screening strategies.