The Predictive Value of Elliptical Neck Parameters and Oversizing Ratio for Type Ia Endoleaks after Endovascular Aneurysm Repair

Purpose: To assess the predictive value of geometric parameters for type Ia endoleak (T1AEL) after endovascular abdominal aortic aneurysm repair and to determine the range of optimal oversizing ratio (OSR) in patients with an elliptical cross-section of the aneurysm neck. Materials and Methods: A propensity score-matched case-control study was conducted. Case patients were those who were diagnosed with T1AEL and control patients were those who did not have T1AEL after endovascular aneurysm repair during the period from 2012 to 2018. Geometric and oversizing parameters were compared based on both 2-dimensional (2D) and 3-dimensional measurements. Net reclassification improvement was used to measure the prediction increment of an elliptical model (major axis OSR, neck length, and severe neck angulation) compared with that of the conventional model (OSR 2D, neck length, and severe neck angulation). Results: Nineteen case patients and 111 control patients were included. The median OSR 2D of patients with T1AEL was 17% (interquartile range, 15%-22%), but the median major axis OSR was only 7% (interquartile range, 5%-12%). For the geometric parameters, axis difference had the highest area under the curve (AUC) (0.74; 95% CI, 0.63-0.84) for predicting T1AEL. For the elliptical oversizing parameters, the major axis OSR had an AUC of 0.89 (95% CI, 0.78-0.97), with a cutoff value of 13%. The elliptical model had a higher discriminating ability for T1AEL than the conventional model (AUC 0.91 vs 0.86, respectively; P = .045), with an improved reclassification ability (net reclassification improvement, 27.93%; 95% CI, 19.22%-36.64%; P < .0001). Conclusions: Elliptical aneurysm neck cross-section, assessed by the difference between axis dimensions in the plane orthogonal to the centerline, was associated with an increased risk of T1AEL. The prescription of major axis oversizing of at least 13% can significantly reduce the risk of T1AEL formation in patients with an elliptical aneurysm neck.