The Value of Volume over Maximum Diameter for Following abdominal aortic aneurysm Growth and Reducing Surveillance Visits in Patients with a Subthreshold aneurysms.

Abstract

Objective: To describe and compare abdominal aortic aneurysm (AAA) volume to maximum diameter regarding follow-up of AAA-progression, and investigate its added value in AAA surveillance.

Methods: This prospective, observational cohort study included 126 patients enrolled in the multicenter BIOMArCS-AAA study who were under surveillance for an AAA. Participants underwent CT-scans at study inclusion and after one and two years, alongside CT-scans for clinical care. Maximum diameter and total volume were measured after center lumen line reconstruction. Mixed-effects regression was used to evaluate maximum diameter and volume changes over time. The value of volume alongside maximum diameter to distinguish patients that will/will not experience the composite endpoint (qualifying for surgery, or AAA-rupture/AAA-related death) was evaluated using Cox-models and cumulative incidence based positive/negative predictive values (PPV/NPV).

Results: A median of 3 scans were available per patient. The baseline median (25^th-75^th percentile) maximum diameter and volume were 48 (45, 52) mm and 109 (90, 130) mL, respectively. The observed median (25^th-75^th percentile) growth at one-year follow-up was 2.3 (1.3, 3.1) mm in maximum diameter, and 10.8 (7.0, 16.4) mL in volume. Changes in aneurysm size at the next recommended surveillance visit lay within the boundaries of the inter-observer variability for 81 (65%) patients when measuring maximum diameter, compared to 43 (34%) patients when measuring volume (p<0.001). Using a single maximum diameter measurement, 32 (26%) patients could be exempt from surveillance imaging at one year, while ensuring that the risk of qualifying for surgery remains below 10%. When combining this with a simultaneous volume measurement, 54 (44%) patients could similarly be safely exempt from surveillance imaging (p=0.002). Moreover, simultaneously measuring volume refines the identification of patients that will qualify for surgery at two years (PPV diameter vs. diameter & volume: 57.7% and 72.5%, p<0.001).

Conclusions: AAA volume is more sensitive to detect small changes in aneurysm size at the currently recommended surveillance intervals, and could be used to safely prolong surveillance intervals for patients with a small AAA. The use of volume should be encouraged in research and could prove valuable in AAA surveillance.