VARIABILITY IN MEASUREMENT OF ABDOMINAL AORTIC-ANEURYSMS

Purpose: The purpose of this study was to report interobserver and int raobserver variability of computed tomography (CT) measurements of abd ominal aortic aneurysm (AAA) diameter and agreement between CT and ult rasonography observed in the course of a large, multicenter, randomize d trial on the management of small AAAs. Methods: CT measurements of A AA diameter from participating centers were compared with measurements made from the same scan by a central laboratory. Blinded central reme asurement of a randomly selected subset of these CT scans was used to assess intraobserver variability. Agreement between AAA measurements b y CT and ultrasonography done within 30 days of each other was also as sessed. Results: For interobserver pairs of local and central CT measu rements of AAA diameter (n = 806), the difference was 0.2 cm or less i n 65% of pairs, but 17% differed by at least 0.5 cm. For intraobserver pairs of central CT remeasurements (n = 70), 90% differed by 0.2 cm o r less, 70% were within 0.1 cm, and only one differed by 0.5 cm. Of 25 8 ultrasound-measured and central CT pairs, the difference was 0.2 cm or less in 44% and at least 0.5 cm in 33%. Ultrasound measurements wer e smaller than central CT measurements by an average of 0.27 cm (p < 0 .0001). Local CT and ultrasound measurements showed a marked preferenc e for recording by half centimeter. Conclusions: A high degree of prec ision is possible in CT measurement of AAA diameter, but this precisio n may not be obtained in practice because of differences in measuremen t techniques. Differences between imaging modalities increase variabil ity further. Variations in AAA measurement of 0.5 cm or more are not u ncommon, and this should be taken into account in management decisions . Efforts to reduce variation in measurement are warranted and might i nclude (1) seeking agreement between surgeons and radiologists on a pr ecise definition of AAA diameter, (2) limiting the number of radiologi sts who measure AAAs, and (3) use of calipers and magnifying glass for CT measurements.