Interobserver Agreement of the Estimated Contact Surface Area System for Renal Masses

Background: Nephrometry scores have been designed to assist in standardization of renal masses before nephron-sparing surgery. Estimated contact surface area (eCSA) has been recently described. However, its reproducibility between raters has not been rigorously explored. Our aim was to examine the reproducibility of eCSA and Radius, Exophytic, Nearness, Anterior, Line (RENAL) score (RS) nephrometry systems for renal masses by studying the interobserver agreement between 4 raters. Materials and Methods: We reviewed the cross-sectional images (computed tomography, magnetic resonance imaging) of patients who underwent nephron-sparing surgery (open, laparoscopic, and robotic). Four urologists independently scored the renal tumors according to the eCSA and RS systems. Scoring was done separately for each nephrometry system. Interobserver agreement was assessed for total scores and separate components of each system by calculating the intraclass correlation coefficient (ICC). Results: Ninety patients were scored to achieve power of 83% with α = 0.05. eCSA and RS demonstrated excellent interobserver agreement (ICC = 0.89 for both). The radius component of eCSA and RS had the highest ICC (0.97 and 0.9, respectively) compared with the other components. Location and anterior/posterior components of RS showed poor interobserver correlation (ICC = 0.69 and 0.50, respectively). Maximal difference in RS complexity group assignment was 1 of 43 (47.8%) of cases. Conclusion: eCSA has excellent interobserver agreement, similar to RS. Directly measurable anatomic variables have better interobserver correlation compared with qualitative variables. These results strengthen the applicability of eCSA as a surgical complexity metric for renal surgery.