Comparison of Mini-Percutaneous Nephrolithotomy and Flexible Ureteroscopy for Treating 1–2 cm Single Stones in Solitary Kidney: Outcomes and Renal Function Impact

<b>Objective</b>: The optimal surgical approach for 1.0-2.0 cm renal stones in solitary kidney patients remains controversial. This retrospective study compared mini-percutaneous nephrolithotomy (mPCNL) and flexible ureteroscopy (f-URS) outcomes in this vulnerable population. <b>Methods</b>: Between June 2018 and April 2024, 50 patients with solitary kidneys and 1.0-2.0 cm renal stones underwent either mPCNL (<i>n</i> = 26) or f-URS (<i>n</i> = 24). Outcomes included 3-month stone-free rate (SFR), complications (Clavien-Dindo classification), and renal function (serum creatinine, eGFR by CKD-EPI equation) at the baseline, 72 h, and 1 month. <b>Results</b>: Stone-free rates were comparable (mPCNL 96.2% vs. f-URS 91.7%, <i>p</i> = 0.157). The f-URS group demonstrated significantly less hemoglobin decline (2.2 ± 0.9 vs. 5.7 ± 2.4 g/dL, <i>p</i> < 0.001) and shorter hospitalization (4.1 ± 1.1 vs. 7.8 ± 1.6 days, <i>p</i> < 0.001). All Grade II complications (8.3%, requiring transfusion) occurred in the mPCNL group. At 1 month, serum creatinine decreased more with f-URS (15.4 ± 7.96 vs. 8.7 ± 4.23 μmol/L, <i>p</i> < 0.001), with greater eGFR improvement (16.7 ± 4.7 vs. 15.4 ± 5.2 mL/min/1.73 m², <i>p</i> = 0.023). <b>Conclusions</b>: In this retrospective cohort, f-URS achieved comparable stone clearance to mPCNL alongside a superior early safety profile and better short-term renal functional preservation. These preliminary findings suggest that f-URS represents a viable nephron-sparing option for this high-risk population. However, these results are considered hypothesis-generating, and further prospective, long-term studies are required to evaluate the durability of these functional benefits.