Maximum Diameter of Native Abdominal Aortic Aneurysm Measured by Angio-Computed Tomography: Reproducibility and Lack of Consensus Impacts on Clinical Decisions

Abstract

Background: Computed tomography angiography (CTA) is the reference technique for the measurement of native maximum abdominal aortic aneurysm (AAA) diameter when surgery is being considered. However, there is a wide choice available for the methodology of maximum AAA diameter measurement on CTA, and to date, no consensus has been reached on which method is best. We analyzed clinical decisions based on these various measures of native maximum AAA diameter with CTA, then analyzed their reproducibility and identified the method of measurement yielding the highest agreement in terms of patient management.

Materials and methods: Three sets of measures in 46 native AAA were obtained, double-blind by three radiologists (J, S, V) on orthogonal planes, curved multiplanar reconstructions, and semi-automated-software, based on the AAA-lumen centerline. From each set, the clinical decision was recorded as follows: "Follow-up" (if all diameters <50 mm), "ambiguous" (if at least one diameter <50 mm AND at least one ≥50 mm) or "Surgery " (if all diameters ≥50 mm). Intra- and interobserver agreements in clinical decisions were compared using the weighted Kappa coefficient.

Results: Clinical decisions varied according to the measurement sets used by each observer, and according to intra and interobserver (lecture#1) reproducibility. Based on the first reading of each observer, the number of AAA proposed for surgery ranged from 11 to 24 for J, 5 to 20 for S, and 15 to 23 for V. The rate of AAAs classified as "ambiguous" varied from 11% (5/46) to 37% (17/46). The semi-automated method yielded very good intraand interobserver agreements in clinical decisions in all comparisons (Kappa range 0.83-1.00).

Conclusion: The semi-automated method seems to be appropriate for native AAA maximum diameter measurement on CTA. In the absence of AAA outer-wallbased software more robust for complex AAA, clinical decisions might best be made with diameter values obtained using this technique.

Keywords: Abdominal aortic aneurysm; Computed tomography; Reproducibility.

Figure 1.

Diameters measured on native axial slices (upper left), sagittal and coronal planes (upper middle and right), on parasagittal, paracoronal curvilinear multiplanar reconstruction (MPR) (middle right and left), and with the semi-automated method (lower right and left). A. Axial slices: antero-posterior diameter Axial_APD (1); transverse diameter Axial_TrD (2); and maximum diameter in any direction Axial_Dmax (3). B. Sagittal MPR image: antero-posterior diameter Sag_APD (4) and diameter perpendicular to the long axis of the aneurysm Sag_PerpD (5). C. Coronal MPR image: transverse diameter Coro_TrD (6) and diameter perpendicular to the long axis of the aneurysm Coro_PerpD (7). D. Parasagittal reconstructed image: antero-posterior diameter perpendicular to the long axis of the aneurysm PSR _PerpD (8). E. Paracoronal reconstructed images: transverse diameter perpendicular to the long axis of the aneurysm PCR _PerpD (9). F. Semi-automated method: cross section containing the maximum aortic diameter in any direction perpendicular to the lumen centerline. The circle corresponds to the initial result obtained with the software, contouring the interface between the aortic lumen opacified by contrast agent and the thrombus. Arrows illustrate the effect of manual drawing of the AAA outer limits (thrombus and walls) performed by the observer. G. Semi-automated method: maximum diameter in any direction (10) automatically calculated once the observer has manually drawn the outer limits of the AAA, including thrombus and the arterial wall (circle).