Comparison Between RIRS and Mini-PCNL in the Treatment of Kidney Stones Exceeding 15 mm: Outcome Evaluation and Cost Analysis

: Background/Objectives: The optimal surgical approach for kidney stones (KS) measuring 15-20 mm remains debated. RIRS and mini-PCNL are both effective options, but they differ in invasiveness, resource use, and cost. This study aimed to compare perioperative outcomes and hospital costs of RIRS and mini-PCNL using a micro-costing approach. Methods: This retrospective study included patients with KS > 15 mm in diameter who were treated between January 2021 and December 2023 at the Department of Urology, Sapienza University of Rome-Polo Pontino. Clinical parameters, operative time (OT), length of stay (LoS), complications, and stone-free rate (SFR) were compared. Costs were estimated using a micro-costing method, including disposable materials, operating room (OR) time (3.9 EUR/min), imaging, and hospitalization (334 EUR/day). The total cost per treated and per SF patient was calculated for both techniques. Results: A total of 119 patients were analyzed: 62 underwent RIRS, and 57 underwent mini-PCNL. Mean OT was shorter for RIRS (87 vs. 113 min; p < 0.001), and LoS was longer for mini-PCNL (2.24 vs. 1.22 days; p = 0.008). Final SFR was higher for mini-PCNL (94.7% vs. 88.7%; p = 0.043). Complication rates were comparable, with most events classified as Clavien-Dindo I-II. Disposable materials represented the main cost driver (EUR 1097 for RIRS vs. EUR 806 for mini-PCNL). The total cost per treated patient was EUR 3689 for RIRS and EUR 3154 for mini-PCNL (p = 0.009). The cost per SF patient was EUR 4159 for RIRS and EUR 3331 for mini-PCNL (p = 0.007). Conclusions: Both RIRS and mini-PCNL are safe and effective for the management of KS ≥ 15 mm. Mini-PCNL achieves higher SFR and greater cost-efficiency than RIRS. These findings support the use of mini-PCNL as the preferred option in centers with adequate expertise and resources.