Stesura Seveso Archivio Italiano di Urologia e Andrologia 2025; 97(1):13336 1 ORIGINAL PAPER INTRODUCTION Around 5-10% of the general population suffer from urolithiasis (1, 2). Majority of the cases presenting with obstructive ureteral calculi require a prompt management to preserve functional and structural status of the involved kidneys which may cause some irreversible changes if not removed on time (3-5). Regarding the management of such cases, ureteroscopy (URS) with laser lithotripsy and percutaneous nephrolitho- tomy (PNL) are the available options applied in the man- agement of obstructing large ureteral calculi (6). Antegrade percutaneous approach is being applied in a certain per cent of the cases with the complete removal of all stone(s) in a single session. However, this procedure is more invasive than other endourological approaches for the risk of certain severe complications (bleeding, perfo- ration, infection, etc) even in experienced hands. In the Objective: To compare the safety and efficacy of retrograde intrarenal surgery (RIRS) versus minimally invasive percutaneous nephrolithotomy (mPCNL) in the minimal invasive management of impacted upper ureteral stones along with the evaluation of predictive radiological parameters. Patients and methods: A retrospective analysis was done in 124 patients, undergoing RIRS (n:61) and mPCNL (n:63) for the management of impacted upper ureteral stones. Both operative (success and complication rates, operative time, postoperative hospital stay) and radiological (ureteral wall thickness (UWT), stone volume (SV), and stone density (Hounsfield unit, HU) factors were all evaluated and recorded. Comparative evalua- tion of stone free status in both groups was done following 72 hours and 4-weeks after the procedures to calculate the primary stone-free as well as final stone clearance rates. Additionally, the outcomes of RIRS group were categorized based on the intraoperative findings (presence or absence of stone encase- ment by a polyp) and preoperative radiological parameters. All data were well analyzed for statistical significance. A signifi- cance level of P<0.05 was considered statistically significant. Results: Baseline patient and stone related characteristics were similar in two groups. The success rates after a single session for RIRS and mPCNL were 73.77% and 93.65%, respectively (p = 0.003), indicating a significantly higher success rate for mPCNL. However the final stone clearance rates were 96.72% and 100.00%, respectively (p = 0.147), with no significant differ- ence observed among the groups. The RIRS group demonstrated higher rate of need for auxiliary treatments (p < 0.001), shorter hospital stay (p < 0.001) and lower incidence of bleeding (p < 0.001). Radiological evaluation showed no significant dif- ferences in stone volume, HU and UWT values between patients with and without residual stones after RIRS (Pstone volume = 0.151, PHU = 0.451, PUWT = 0.083). Similarly, no significant differences were observed with respect to these values also in mPCNL patients, (Pstone volume = 0.532, PHU = 0.455, PUWT = 0.658). However, a significant difference has been noted regarding the mean value of UWT between the stones surround- Comparative evaluation of the efficacy and safety of antegrade minimally percutaneous nephrolithotomy (mPCNL) and retrograde intrarenal surgery (RIRS) in the treatment of upper ureteral impacted stones: A retrospective cohort study Kequan Cheng 1, 2*, Xuwei Hong 1*, Gang Wang 1, 2, Zepai Chi 1, Kemal Sarica 3, 4, Guoyuan Liu 1, Yonghai Zhang 1 1 Department of Urology, Shantou Central Hospital, Shantou, Guangdong, P.R. China; 2 Department of Urology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, Guangdong, P.R. China; 3 Department of Urology, Health Sciences University, Prof. Dr. Ilhan Varank Education and Training Hospital, Istanbul, Turkey; 4 Department of Urology, Biruni University, Medical School, Istanbul, Turkey. * These authors contributed equally to this work. DOI: 10.4081/aiua.2025.13336 Summary ed by a polypoid alterations and the ones without such changes with values 5.23 ± 0.65 mm, to 4.10 ± 0.82 mm respectively (p = 0.001). Conclusions: Our results demonstrated that antegrade mPCNL achieves faster stone clearance and a lower re-treatment rate without serious complications in impacted upper ureteric stones. However, RIRS could be a valuable and safe alternative with comparable success rates particularly in cases with con- traindications to or unwillingness for mPCNL. Preoperative assessment of ureteral wall thickness (UWT) value may be a good predictor for the possible tissue changes in ureteral wall at stone site to guide the decision making of the most appropri- ate surgical approach. KEY WORDS: Percutaneous nephrolithotomy; Retrograde intrarenal surgery; Ureteral impacted stones; Retrospective study. Submitted 4 November 2024; Accepted 28 November 2024 Archivio Italiano di Urologia e Andrologia 2025; 97(1):13336 K. Cheng, X. Hong, G. Wang, et al. 2 light of the risk for such complications endourologists began to use smaller instruments in an attempt to limit both the extent of renal injury and also the risk of above mentioned complications (7, 8). Miniaturized PCNL techniques are being utilized with higher success and lim- ited complications in the majority of cases presenting with large upper tract stones (9). On the other hand, based on its less invasive nature and successful outcomes compared with PCNL, flexible ureteroscopic management gained more popularity in the last 2-3 decades as a result of the evident advances in instrument technology. Based on these improvements and acceptable outcomes obtained the joint clinical guidelines of the AUA and the EAU Nephrolithiasis Panel on the Management of Ureteral Calculi recommend URS in patients with proximal ureteral stones smaller than 2 cm (10). Additionally, the most recent EAU and AUA guidelines also recommend URS as the primary modality for stones > 10 mm (1, 11). This modality may serve as a viable alternative treatment particularly in patients with contraindications to PCNL or whom do not prefer to undergo such a more invasive intervention (12). However, accumulated data have shown that despite its evident minimally invasive nature, ureteroscopic manipulation may be associated with cer- tain complications such as ureteral injuries and subse- quent ureteral stricture formation (13). Additionally, relatively lower stone-free rates (SFR) and the need for additional auxiliary procedures (14, 15) remain significant challenges for this technique when particularly dealing with large stones. Some stone related parameters have been identified and used to predict the outcomes of Retrograde Intrarenal Surgery (RIRS) in the management of large, impacted ureteral stones causing certain degree of obstruction. Related with this issue in addition to the size, volume, density and chemical com- position of the stones treated, the thickness of the ureteric wall surrounding the impacted stone(s) have been used with great success to predict both the success as well as complications of RIRS in such cases (16). Taking the advantages and disadvantages of both modal- ities into account, in this study we aimed to compare the clinical results of RIRS and mPCNL in the management of single impacted upper ureteral stones less than 2 cm in diameter. Also, the potential value of some radiological parameters in the prediction of success after RIRS were evaluated to select the most appropriate surgical method in these stones. PATIENTS AND METHODS A retrospective analysis was conducted in 124 patients with upper ureteral impacted stones (< 2 cm) admitted to our urology department from April 2020 to December 2023. Based on the type of intervention applied, patients were divided into two groups: Group 1 (n:61) including patients undergoing RIRS with laser lithotripsy and Group 2 (n:63) including patients undergoing mPCNL. An informed consent was obtained in all cases undergo- ing both interventions. Inclusion criteria were unilateral single upper ureteral stones (< 2 cm) confirmed by non-contrast computed tomog- raphy (NCCT). Exclusion criteria included patients with active urinary tract infections, previous renal-ureteral inter- ventions, renal functional deterioration and anatomical abnormalities contraindicating surgery. In addition to a detailed history and through urogenital examination, blood/urine analyses were done in all patients. Patients with urinary tract infections were previously treated according to the outcomes of culture-sensitivity tests. Radiological evaluation consisted of kidney-ureter-bladder (KUB) film, sonography and NCCT in all cases. An intra- venous urography was performed in cases requiring further anatomical information for making a proper decision. Demographic data, including age and sex, medical history, and stone side, size, and location, were recorded (see Table 1). Surgical duration, length of hospital stays, perioperative complications, and treatment outcomes were evaluated and compared between groups. Additionally, Hounsfield units (HU) value of the stone, ureteral wall thickness (UWT) and maximum transverse and longitudinal diameter of the stones were measured on NCCT and noted. KUB X-ray was obtained within 72 hours of post-operative period to con- firm the correct placement of double-J stents and to assess residual stone status. Surgical success was defined as the absence of fragment or presence of residual stone frag- ments smaller than 3 mm following the procedures. Residual stones were treated with extracorporeal shock wave lithotripsy (ESWL) or external physical vibration lithotripsy (EPVL). DJ stents were removed after two weeks, and all patients were followed up one month postoperatively in the outpatient or inpatient department to outline the status of final stone clearance. Definitions of outcome measures Surgical efficacy: Assessed the results of 72-hour and one- month follow-up, including technical success rate and stone-free rate. Operative Time: For RIRS, timing com- menced with the placement of the flexible ureteroscope sheath, or the guidewire passing the stone and concluded with the successful placement of the ureteral stent. For mPCNL, timing began with the percutaneous puncture and ended with the successful placement of the nephrosto- my tube. Postoperative Hospital duration: The duration from the day of surgery until discharge. Postoperative Auxiliary Treatment Rate: Number of cases requiring ESWL and EPVL based on follow-up KUB results. Postoperative Complications: Postoperative Complications were classi- fied according to the Clavien-Dindo system, including the number of cases requiring hemostatic agents, those with postoperative fever, and those needing pain medication within 24 hours of surgery. Surgical procedure RIRS: The procedure was performed in the lithotomy posi- tion under general or combined spinal-epidural anesthesia. A 0.035-inch Wolf guidewire was passed into the ureter through the rigid Fr 8.0 to 9.8 Wolf ureteroscope was and stone localization was confirmed by using low-pressure irri- gation. Fragmentation of the stone was performed with the help of either holmium laser or pneumatic ballistic lithotrip- Archivio Italiano di Urologia e Andrologia 2025; 97(1):13336 3 mPCNL vs RIRS for upper ureteral impacted stones sy. The holmium laser settings were arranged with a fre- quency value of 10 Hz, energy value of 800 J, and pressure value of 14 kPa. While larger fragments were extracted with the help of stone forceps, dust and smaller fragments were flushed out. The procedure was finished with the routine placement of a 5-Fr double-J stent in the affected ureter. A urethral catheter was left in place for 1 to 2 days. mPCNL: Following the placement of a 5Fr open end ureter- al catheter during cystoscopic evaluation in lithotomy posi- tion under general anesthesia, later the patient was turned into prone position and renal puncture was performed with a 18-gauge puncture needle under ultrasound guid- ance. Upon achieving puncture to the dependant calyx, a 0.035-inch guidewire was inserted into the collecting sys- tem whit following a 1 cm skin incision, fascial dilation and placement of a 18-Fr working sheath. A 17-Fr nephro- scope was introduced through the working sheath for stone fragmentation. Stones were disintegrated using either a holmium laser or pneumatic ballistic lithotripsy and all fragments were removed. A nephrostomy tube was insert- ed if necessary. Following the removal of all stone frag- ments a 5-French double-J stent was placed antegradely into the affected ureter. A urethral catheter was placed and retained for 1 to 2 days as needed. Radiologic evaluation of the stones and relevant parameters NCCT images were analyzed by two radiologists to meas- ure the ureteral wall thickness (UWT) at the stone location by taking the maximum value from cross-sectional images. Hounsfield unit (HU) value of the stone was meas- ured at the stone's central region, avoiding the boundary with surrounding soft tissue. Maximum longitudinal and transverse diameter of the stones were measured in coro- nal and transverse planes. Stone surface area (SA) and volume (V) were estimated using the following formulas based on EAU guidelines (10): SA (mm²) = l × w × π × 0.25 (Formula 3-1) V (mm³) = 0.6 × SA1.27 (Formula 3-2) (l = maximum longitudinal diameter, w = maximum transverse diameter) Degree of hydronephrosis was classified based on preop- erative ultrasound or CT measurements of renal pelvis separation as mild, moderate, or severe. Statistical analysis Data were analyzed using SPSS 26.0 software. For quan- titative data, independent samples t-tests were used for normally distributed data, and Wilcoxon rank-sum tests for non-normally distributed data. Categorical data were analyzed using chi-square tests. Statistical significance was set at p < 0.05. RESULTS Comparative evaluation of the efficacy rates A total of 124 adult patients were included in the study. There were no statistically significant differences between the two groups in terms of demographic characteristics such as sex, age, medical history, stone side, location, and size (Table 1). Comparative evaluation of the peri- and postoperative parameters are given in Table 2. Although there was a sig- nificant difference in the operative success rates between the two groups (p < 0.05), no significant difference could be noted in the stone-free rates of two groups. Of the 61 cases in RIRS group, 14 required additional procedures (ESWL or EPVL) to achieve a complete stone-free status. The auxiliary treatment rate was higher in the RIRS group compared to the mPCNL group (p < 0.05). Table 1. Preoperative baseline characteristics of patients in the MPCNL and RIRS groups. RIRS (n = 61) MPCNL (n = 63) χ2/t P Sex/cases (%) Female 25 (40.98) 22 (34.92) 0.48 0.487 Male 36 (59.02) 41 (65.08) Age (mean SD) 53.82 (14.61) 54.68 (13.05) -0.35 0.729 Side of the stone/cases (%) Left 38 (62.29) 32 (50.79) 1.67 0.197 Right 23 (37.71) 31 (49.21) Medical history/cases (%) Diabetes 6 (9.84) 12 (19.05) 2.12 0.145 Coronary heart disease 4 (6.56) 1 (1.59) 1.98 0.160 Hypertension 19 (31.15) 19 (30.16) 0.01 0.905 COPD1 0 (0.00) 1 (1.59) 0.98 0.323 BPH2 9 (14.75) 7 (11.11) 0.37 0.545 Operational history/cases (%) ESWL 7 (11.48) 3 (4.76) 1.88 0.170 RIRS 4 (6.56) 1 (1.59) 1.98 0.160 PCNL 0 (0.00) 1 (1.59) 0.98 0.323 Imaging characteristics (mean SD) UWT/mm 4.23 (0.88) 4.02 (0.90) 1.30 0.196 HU 1150.38 (258.18) 1158.81 (263.38) -0.18 0.857 Transverse diameter/mm 11.25 (2.37) 10.81 (1.82) 1.16 0.247 Longitudinal diameter/mm 14.45 (3.80) 14.48 (3.21) -0.04 0.966 Hydronephrosis/cases (%) Mild 26 (42.62) 20 (31.75) 3.95 0.139 Moderate 20 (32.79) 17 (26.98) Severe 15 (24.59) 26 (41.27) Mean SD: Mean Standard Deviation; 1 Chronic obstructive pulmonary disease; 2 Benign prostatic hyperplasia. Table 2. Postoperative efficacy and safety outcomes of RIRS and MPCNL. RIRS (n = 61) MPCNL (n = 63) χ2/t P Operation success rate (%) 45 (73.77) 59 (93.65) 9.05 0.003 Stone clearance rate (%) 59 (96.72) 63 (100.00) 2.10 0.147 Postoperative adjunctive therapy (%) 14 (22.95) 1 (1.59) 13.30 ＜0.001 Operation time/min (mean ± SD) 69.41 (36.11) 72.33 (29.93) -0.49 0.624 Hospital stay/days (mean ± SD) 2.98 (1.58) 4.76 (2.32) -5.01 ＜0.001 Infection case (%) 8 (13.11) 3 (4.76) 2.67 0.102 Bleeding/case (%) 1 (1.63) 19 (30.16) 18.63 ＜0.001 Analgesic use/case (%) 49 (80.33) 50 (79.37) 0.02 0.894 Mean (SD) indicates the mean (standard deviation). Archivio Italiano di Urologia e Andrologia 2025; 97(1):13336 K. Cheng, X. Hong, G. Wang, et al. 4 Complications were classified by using the Clavien-Dindo grading system and no Grade IV complication was noted in any case of this study. There was no statistically sig- nificant difference regarding the postoperative pain between the two groups. However, use of the hemostatic drugs was more frequent (30.16%) in the mPCNL group where one patient received blood transfusion and one underwent interventional treatment for bleeding demon- strating a statistically significant difference (p < 0.05) between two groups with respect to this complication. There was no significant difference between the two tech- niques regarding the postoperative need for pain medica- tion within 24 hours and infective complication rates. Last but not least, the average hospital stay was 2.98 ± 1.58 days in the RIRS group and 4.76 ± 2.32 days for the mPCNL group respectively, indicating a relatively longer recovery time observed in the mPCNL group (p < 0.05). Evaluation of the radiological parameters Comparative analysis of the possible relationship between treatment outcomes and mean stone related parameters (volume and HU) as well as mean UWT values revealed no statistically significant differences between two group of cases (PRIRS-stone volume = 0.151 > 0.05, PRIRS-HU = 0.451 > 0.05, PRIRS-UWT = 0.083 > 0.05; PmPCNL- stone volume = 0.532 > 0.05, PmPCNL-HU = 0.455 > 0.05, PmPCNL-UWT = 0.658 > 0.05) (Tables 3, 4). A retrospective analysis of our data revealed that the RIRS group had a lower success rates in a single session com- pared to the mPCNL group, often requiring additional ESWL or EPVL. Further analysis of success rates in RIRS group demonstrated that stone free rates were significant- ly affected by the changes in the ureteral wall characteris- tics (Table 5). While 36 out of 61 cases in this group had inflammatory polyps noted during the procedure, 6 had strictures and 7 had stones encased by polyps, which could complicate guidewire placement, increase the risk of intraoperative bleeding, and necessitate multiple ureteroscope manipu- lations causing additional trauma. Based on this fact, fur- ther detailed analysis on the preoperative imaging find- ings and the presence of intraoperative polyps encasing stones was conducted, as demonstrated in Table 5. The mean preoperative UWT value detected in NCCT imaging was significantly higher in cases with stones encased by polyps (5.23 ± 0.65 mm), (P_UWT = 0.001). In contrast, there was no statistically significant difference in the mean stone volume and mean HU values (P_stone volume = 0.441, P_HU = 0.711). DISCUSSION Currently both anterograde PCNL and RIRS are accept- able options for the minimal invasive management of impacted proximal ureteral stones with varying rates of success and complications in different series (17). Each modality has its own advantage and disadvantages and accumulated experience so far demonstrated that despite its higher stone free rates in a single session, even mini- PCNL could be associated with severe complications (18- 20). On the other hand, with the use new generation flex- ible scopes with Ho-YAG laser technology, RIRS was found to reveal comparable stone free rates with limited rate of complications particularly in risk group of cases for PCNL (21). Taking all these facts into account, in this present study we aimed to evaluate the efficacy and safety of both modalities in the management of impacted upper ureter- al stones causing obstruction. Additionally, we evaluated the some certain radiological parameters in an attempt to predict the outcomes of RIRS in such stones and their possible role in the preoperative decision making phase to outline the best modality. Evaluation of our obtained data revealed the following findings. Evaluation of success rates and the need for auxiliary treatment Our results demonstrated a significant difference between success rates in terms of stone free status during short term evaluation between the two modalities where RIRS approach seemed to be less effective. Additionally, Table 3. Comparison of imaging data of residual stones after RIRS surgery. No residual stones Residual stones (n = 59) (n = 4) t P Stone volume/mm3 (mean ± SD) 92.30 (30.19) 124.27 (83.00) -2.23 0.151 HU (mean ± SD) 1135.38 (279.19) 1192.56 (188.15) -0.76 0.451 UWT/mm (mean SD) 4.12 (0.84) 4.56 (0.94) -1.76 0.083 HU stands for Hounsfield Units, a measure used in CT scans; UWT stands for ureteral wall thickness; Mean SD indicates the mean standard deviation. Table 5. Comparison of imaging data for cases with and without polyp encapsulation in RIRS group. Stone Stone t-value P-value without polyp with polyp encapsulation encapsulation (n = 54) (n = 7) Stone volume/mm3 (mean SD) 102.51 (53.45) 86.61 (20.52) 0.78 0.441 HU (mean SD) 1154.83 (266.86) 1116.00 (189.54) 0.37 0.711 Ureteral wall thickness/mm 4.10 (0.82) 5.23 (0.65) -3.48 0.001 HU stands for Hounsfield Units, a measure used in CT scans; UWT stands for ureteral wall thickness; Mean SD indicates the mean standard deviation. Table 4. Comparison of imaging data of residual stones after MPCNL surgery. No residual stones Residual stones (n = 45) (n = 16) t P Stone volume/mm3 (mean ± SD) 93.33 (29.36) 118.96 (72.48) -0.70 0.532 HU (mean ± SD) 1152.29 (265.82) 1255.00 (233.13) -0.75 0.455 UWT/mm (mean SD) 4.01 (0.90) 4.22 (0.94) -0.04 0.658 HU stands for Hounsfield Units, a measure used in CT scans; UWT stands for ureteral wall thickness; Mean SD indicates the mean standard deviation. Archivio Italiano di Urologia e Andrologia 2025; 97(1):13336 5 mPCNL vs RIRS for upper ureteral impacted stones patients undergoing RIRS procedure required higher need for adjunctive treatments to achieve outcomes sim- ilar to mPCNL. As a certain advantage, mPCNL was asso- ciated with the advantage of effective fragmentation of the stones from above enabling rapid expulsion of resid- ual fragments under high-pressure irrigation coupled with the enhanced clarity. Despite marked advances in RIRS technology, such as improved irrigation systems and larger working channels, flexible ureteroscopy tech- nique remains less effective in stone fragmentation com- pared to mPCNL (22). Related with this issue, Faruk et al., found that flexible ureteroscopic management is effective for upper ureteral stones (average size of 1.24 cm), with a 96.4% single-ses- sion success rate (23). However, flexible ureteroscopic stone management was found to exhibit promising results in challenging cases such as obese and pediatric patients. In their original study Best et al. were able to demonstrate a single-session success rate of 91% obese patients undergoing flexible ureteroscopic lithotripsy (24). Regarding the disadvantages of RIRS compared to mini-PCNL, the complex nature of the procedure with its high equipment costs and maintenance expenses seemed to limit the widespread use of RIRS (25). Stone fragmen- tation and removal may also be less practical and effec- tive during RIRS compared to mPCNL where dust form- ing during the procedure can cause blurred vision mak- ing the identification of small fragments hard for the sur- geon. However, recent technological advancements with the introduction of new effective laser types and suction device will certainly help to improve the success rates of RIRS, as in studies indicating good results for relatively larger stones (26). In fact Mulţescu et al. and Cho et al. were able to demonstrate that stones larger than 1 cm could be well pulverized in a successful manner with flexible ureteroscopic approach (27). Evaluation of the procedure related complications Complications with mPCNL are primarily linked to puncture and stone fragmentation, including severe risks like bleeding, upper urinary tract perforation, renal func- tion deterioration and injury to adjacent organs.(28, 29) In the retrospective study of 10.413 cases of F-URL treat- ment patients by Xu et al. (30) the incidence rate of com- plications with electronic ureteroscopy soft mirrors did not exceed 1%. In our study, 8 patients in the RIRS group experienced postoperative infective problems, which were well treated with appropriate antibiotic treatment. Among these, 3 cases experienced fever possibly due to bacteremia from stone fragmentation. Regarding the bleeding complication while postoperative hematuria generally improved well within one day after the procedure in RIRS cases, cases in mPCNL group required more hemostatic drugs, with one case requiring interventional treatment for severe bleed- ing. Thus, mPCNL generally involves more postoperative complications and higher management demands. Evaluation of ureteral wall thickness value on the outcomes of RIRS Mean ureteral wall thickness (UWT) values did not show any statistically significant difference between the two groups with or without residual stones for either specific technique. Possible reasons include: 1) UWT measure- ments can be influenced by factors such as the surgeon’s experience, scan thickness, and CT image quality; (31) 2) Large stones are frequently associated with ureteral anomalies, which can lead to measurement errors. In this study, 5 cases in the RIRS group exhibited significant ureteral tortuosity, necessitating image aggregation from three planes to achieve more accurate UWT values. Subgroup analysis revealed that stones encased by polyps in the RIRS group had significantly mean higher UWT val- ues, indicating that preoperative measurement of UWT may be an effective predictor for the presence of polyps encasing stones. Elevated UWT was found to be associated with ureteral inflammatory proliferation.(16) Our results indicate that measurement of UWT value may help to pre- dict stone related ureteral changes and guide urologists in decision making phase to choose the most appropriate option for a successful and complication free procedure. Mini PCNL approach could be a reasonable alternative in such cases by avoiding RIRS for polyp-encased stones to minimize the risk of procedure related complications. Limitations Our study is not free of limitations. First of all the retro- spective, single-center nature of the study design could be stated as the main limitations. Additionally, relatively small size of the sample along with a shorter follow-up period (one month) are additional limitations. We believe that further randomized controlled trials would further support the validity of these findings. Clinical observa- tions indicate that impacted stones are often accompanied by varying degrees of ureteral tortuosity, which may intro- duce measurement errors. Additionally, inflammatory reactions leading to congestion and edema can cause the ureteral wall to have a density similar to surrounding soft tissues, resulting in measurement bias. Utilizing imaging techniques to accurately measure ureteral wall area (UWA) and extract imaging features could provide new insights for developing individualized treatment plans for patients with upper ureteral impacted stones (32). 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Safety and efficacy of minimally invasive percutaneous nephrolithotomy in the treatment of patients with medullary sponge kidney. Urolithiasis. 2016; 44:421-6. 29. de la Rosette JJ, Opondo D, Daels FP, et al. Categorisation of DECLARATIONS Ethical approval: The study was approved by the Institutional Review Board of Shantou Central Hospital. Availability of data and material: The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request. Competing interests: These authors declare that they have no conflict of interest. Funding: This study was supported by the Special Fund Project for Science and Technology Innovation Strategy of Guangdong Province (Grant No. STKJ202209068). Authors' contributions: Conception and design: YZ, KS and GL; Data analysis and interpretation: KC and GW; Data acquisition: XH and ZC; Critical revision of the manuscript: YZ, KS and GL; Drafting the manuscript: KC and XH; Statistical analysis: KC, XH; Supervision: YZ. All authors read and approved the final version of the manuscript. Acknowledgments: Not applicable. Consent for publication: Not applicable. Archivio Italiano di Urologia e Andrologia 2025; 97(1):13336 7 mPCNL vs RIRS for upper ureteral impacted stones complications and validation of the Clavien score for percutaneous nephrolithotomy. Eur Urol. 2012; 62:246-55. 30. Xu G-b, Li X-z, He Y-z, et al. Ten years experience in treatment of upper urinary calculi withRIRS: clinical analysis of 10 413 cases in single center. Chin J Endosc. 2020; 26:64-8. 31. Popiolek M, Lidén M, Georgouleas P, et al. Radiological signs of stone impaction add no value in predicting spontaneous stone pas- sage. Urolithiasis. 2024; 52:114. 32. Yamashita S, Kohjimoto Y, Iguchi T, et al. Ureteral wall volume at ureteral stone site is a critical predictor for shock wave lithotripsy outcomes: comparison with ureteral wall thickness and area. Urolithiasis. 2020; 48:361-8. Correspondence Kequan Cheng, MD chengkq2021@163.com Xuwei Hong, MD hong_xuwei@sina.cn Gang Wang, MD 1031020787@qq.com Zepai Chi, MD zepaichist@126.com Guoyuan Liu, MD liuguoyuan91@sohu.com Department of Urology, Shantou Central Hospital, Shantou, Guangdong, P.R. China Kemal Sarica, MD saricakemal@gmail.com Department of Urology, Health Sciences University, Prof. Dr. Ilhan Varank Education and Training Hospital, Istanbul, Turkey Yonghai Zhang, MD (Corresponding Author) zhang_yonghai@126.com Department of Urology, Shantou Central Hospital 114th Waima Road, Shantou, Guangdong, P.R. China