Pelvic stone angle as a novel parameter for predicting stone-free rates after RIRS: A retrospective comparative analysis with established scoring systems-AUSET collaboration.

Abstract

Background: Several scoring systems have been developed to predict stone-free rates (SFR) after retrograde intrarenal surgery (RIRS), but their clinical utility remains limited. The pelvic stone angle (PSA) has recently been proposed as a novel anatomical parameter for evaluating lower pole stones.

Objectives: To evaluate the predictive value of PSA for stone-free outcomes after RIRS and compare the performance of PSA-integrated scoring systems with existing nephrolithometric models.

Design: Retrospective single-center cohort study.

Methods: A total of 198 patients who underwent RIRS between April 2018 and October 2023 were retrospectively reviewed. Patients with lower pole stones were included. Preoperative non-contrast computed tomography was used to evaluate PSA, stone burden, and other anatomical parameters. Stone-free status was assessed one month postoperatively. Four scoring systems (MS-ReSC, R.I.R.S., RUSS, and T.O.HO.) were analyzed, with PSA replacing the conventional infundibulopelvic angle where applicable. Predictive performance was evaluated using area under the receiver operating characteristic curve (AUC).

Results: The T.O.HO. score demonstrated the highest predictive performance for stone-free status with an AUC of 0.7080, followed by the R.I.R.S. score with PSA (0.6525), MS-ReSC (0.6147), and RUSS with PSA (0.6121). Among the evaluated models, only the T.O.HO. score showed a statistically significant improvement compared with RUSS (p = 0.0445). No statistically significant differences in overall accuracy were observed among the scoring systems. Lower pole stone burden, stone multiplicity, CT attenuation values, and multifocal stones were significantly associated with postoperative stone-free outcomes.

Conclusion: PSA is a practical and reliable anatomical parameter for predicting stone-free outcomes after RIRS. Integration of PSA into existing scoring systems maintained comparable predictive performance and may improve reproducibility in modern endourological practice. Although the T.O.HO. score demonstrated the best overall performance, further large-scale prospective multicenter studies are required to validate PSA-based scoring systems.