Factors Associated with Uncomplicated Single-Session Stone-Free Status After Retrograde Intrarenal Surgery for Large Renal Stones.

Background: To identify predictors of uncomplicated single-session stone-free (USSSF) outcomes after retrograde intrarenal surgery (RIRS) for large renal stones and to compare the performance of contemporary nephrolithometry systems. Methods: We retrospectively analyzed 158 patients who underwent RIRS for 20-40 mm renal stones. Demographic, stone-related, anatomical, and perioperative variables were recorded. R.I.R.S., RUSS, modified S-ReSC, CROES, Ito nomogram, TOHO, and STONE scores, as well as the renal parenchyma-to-renal volume ratio, were calculated from preoperative non-contrast computed tomography images. USSSF was defined as achievement of stone-free status or clinically insignificant residual fragments (CIRFs <4 mm) after a single RIRS session, without postoperative complications, retreatment, or auxiliary procedures. Logistic regression and receiver operating characteristic analyses were performed. Results: USSSF was achieved in 90 patients (56.9%). Lower stone burden, fewer stones, absence of hydronephrosis or abnormal renal anatomy, no previous intervention, and greater surgeon experience were associated with USSSF. On multivariable analysis, higher CROES and Ito's nomogram scores independently predicted USSSF, whereas higher TOHO and RUSS scores were associated with lower success rates. Among all nephrolithometry systems, the CROES score and Ito's nomogram demonstrated the highest discriminative ability (area under the receiver operating characteristic curve [AUC], 0.896 and 0.862, respectively). Conclusions: In patients undergoing RIRS for 20-40 mm renal stones, the CROES score and Ito's nomogram were the strongest predictors of achieving USSSF. These scores may be useful for preoperative patient counselling and risk stratification in selected patients with complex renal stones.