Validating pelvic stone angle as a substitute for infundibulopelvic angle in RIRS outcome prediction

The infundibulopelvic angle (IPA) is a well-established predictor of stone-free rate (SFR) following retrograde intrarenal surgery (RIRS), particularly for lower pole stones. The pelvic stone angle (PSA) has been proposed as a simpler alternative. This study aimed to externally validate PSA and assess its utility relative to IPA and other scoring systems.

We retrospectively reviewed 110 patients with lower pole renal stones who underwent RIRS between January 2022 and January 2024 at a single center. PSA, IPA, RIRS score, and Resorlu-Unsal Stone Score (RUSS) were calculated independently by five urologists, and averaged values were analyzed. Stone-free status was defined as no residual fragments >2 mm on CT within three months. Predictive performance was assessed using logistic regression and ROC analysis.

Among 110 patients, 58.2 % achieved stone-free status. Although PSA was not statistically different between stone-free and non-stone-free groups, the R.I.R.S. scoring system incorporating PSA (AUC = 0.7242) showed comparable predictive performance to the IPA-based model (AUC = 0.7021, p = 1.000). Both PSA and IPA were significantly associated with SFR in multivariate analysis. Cronbach's α values for PSA and IPA exceeded 0.95, indicating high interobserver reliability.

This study confirms that PSA is a viable substitute for IPA in predicting SFR after RIRS, with comparable accuracy and reliability. As an external validation of previous findings, our results support the broader adoption of PSA in clinical scoring systems. Future studies should further investigate PSA's role in newer surgical settings, including suction-assisted RIRS.