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

Area of Science:

• Urology
• Endourology
• Nephrolithiasis Management

Background:

• The infundibulopelvic angle (IPA) is a recognized predictor of stone-free rates (SFR) after retrograde intrarenal surgery (RIRS), especially for lower pole renal stones.
• The pelvic stone angle (PSA) has been proposed as a simpler alternative measurement.
• External validation of PSA's utility compared to IPA and other scoring systems is needed.

Purpose of the Study:

• To externally validate the pelvic stone angle (PSA) as a predictor of stone-free rate (SFR) after retrograde intrarenal surgery (RIRS).
• To assess the utility of PSA relative to the infundibulopelvic angle (IPA) and other established scoring systems.
• To evaluate the interobserver reliability and predictive performance of PSA.

Main Methods:

• Retrospective review of 110 patients undergoing RIRS for lower pole renal stones.
• Independent calculation of PSA, IPA, RIRS score, and Resorlu-Unsal Stone Score (RUSS) by five urologists.
• Logistic regression and ROC analysis to assess predictive performance for stone-free status (no residual fragments >2 mm on CT).

Main Results:

• 58.2% of patients achieved stone-free status.
• The RIRS scoring system incorporating PSA demonstrated comparable predictive performance (AUC=0.7242) to the IPA-based model (AUC=0.7021).
• Both PSA and IPA were significantly associated with SFR in multivariate analysis, with high interobserver reliability (Cronbach's α > 0.95).

Conclusions:

• PSA is a viable and reliable substitute for IPA in predicting SFR after RIRS, exhibiting comparable accuracy.
• The findings support the broader adoption of PSA in clinical scoring systems for renal stone management.
• Further investigation into PSA's role in novel surgical techniques, such as suction-assisted RIRS, is warranted.