Introduction. One of the main trends in the evolution of endoscopic treatment of urolithiasis is the miniaturization of instruments. This is obvious in the development of minimally invasive percutaneous nephro-lithotomy (PCNL) and retrograde intrarenal surgery (RIRS). However, there are few studies comparing the efficiency and safety of these methods.
Aim. To evaluate and compare the efficiency and safety of mini-PCNL, micro-PCNL and RIRS in the treatment of kidney stones up to 2 cm in size.
Materials and methods. Between October 2020 and December 2022, a total 72 patients underwent minimally invasive endoscopic procedures in two centers, including RIRS (n=30), mini-PCNL (n=26) and micro-PCNL (n=16) using thulium fiber laser FiberLase U2. The efficiency of procedure (stone free rate [SFR]) was assessed using non-contrast-enhanced CT. SFR was considered as the absence of residual fragments > 4 mm. Complications (safety) were evaluated based on the Clavien-Dindo classification.
Results. The mean age of all patients was 47.7 (22–84) years. There were no significant differences between three groups in stone characteristics according to CT (maximum diameter, density, volume and number of stones, the presence of pelvicalyceal dilation). SFR was significantly different between the groups (p=0.034). The overall SFR was 81.9% (n=59). After RIRS, mini-PCNL, and micro-PCNL the SFR was 93.3%, 80.8%, and 62.5%, respectively. A significant difference was found between the RIRS and micro-PNL groups, with 2 out of 30 and 6 out of 16 patients requiring repeat procedure, respectively (p=0.026). The overall rate of complication of grades I-II, IIIa and IIIb according to Clavien-Dindo was 6.9%, 9.7% and 6.9%, respectively. A significant difference was found between the RIRS and micro-PCNL (p=0.021) for grade I-II complications. A rate of grade III complications was not differed between the groups. The operation time was higher for mini-PNL (79.8 (30–145) min), and it was shorter for RIRS (55.7 (30–155) min). The length of stay was lower in RIRS group (4.5 (1–12) days).
Conclusion. The highest SFR was achieved in the RIRS group. In terms of the number of complications of I-II grades according to Clavien-Dindo, the duration of the procedure and the length of stay, RIRS also showed the advantage. There were no significant differences in efficiency and safety between the micro-PNL and mini-PNL. There are not enough studies comparing minimally invasive methods for treating kidney stones. It is necessary to continue research in this area in order to develop an optimal algorithm for choosing the method of endoscopic treatment.

Keywords: retrograde intrarenal surgery, stone-free rate, percutaneous nephrolithotomy, urolithiasis