Optimal duration of pre-stenting before RIRS: a prospective randomized study evaluating FANS-UAS placement success

Purpose To evaluate the impact of pre-stenting duration on flexible and navigable ureteral access sheaths (FANS-UAS) placement, as well as perioperative and postoperative outcomes, in patients undergoing retrograde intrarenal surgery (RIRS). Methods A total of 221 patients were prospectively randomized into three groups: no pre-stenting (Group 1, n = 70), pre-stenting for 2–4 weeks (Group 2, n = 74), and pre-stenting for 4–6 weeks (Group 3, n = 77). Analyses were performed according to the intention-to-treat principle. The primary outcome was successful FANS-UAS placement. Secondary outcomes included successful RIRS, stone-free rate (SFR), stone-related secondary procedures, perioperative parameters, and postoperative complications. Post hoc pairwise comparisons and multivariable logistic regression analyses were performed to identify factors associated with FANS-UAS placement success. Results FANS-UAS placement success differed significantly among the groups, increasing from 80.0% in Group 1 to 93.2% and 94.8% in Groups 2 and 3, respectively (p = 0.006). Stone access time was markedly shorter in the pre-stented groups (p < 0.001). Successful RIRS (87.1%, 94.6%, and 94.8%; p = 0.146), SFR (84.3%, 87.8%, and 88.3%; p = 0.672), and secondary procedure rates (17.1%, 12.2%, and 7.8%; p = 0.224) were comparable among the groups. Post hoc analysis demonstrated meaningfully higher FANS-UAS placement success in pre-stented patients compared with non-stented patients, whereas no difference was observed between 2 and 4 and 4–6 weeks of pre-stenting. In multivariable logistic regression analysis, pre-stenting remained the only independent predictor of successful FANS-UAS placement (Group 2 vs. Group 1: adjusted OR 3.47, 95% CI 1.14–10.59, p = 0.029; Group 3 vs. Group 1: adjusted OR 5.31, 95% CI 1.60–17.68, p = 0.006). Clinically significant complications (≥ Grade III) were similar among the groups (12.9%, 12.2%, and 7.8%; p = 0.558). Conclusions Pre-stenting was independently associated with improved FANS-UAS placement success and facilitated ureteral access during RIRS. No statistically significant differences were detected between patients who underwent 2–4 weeks and those who underwent 4–6 weeks of pre-stenting.