ENDOUROLOGY AND STONE DISEASE Flexible Ureterorenoscopy versus Mini-Percutaneous Nephrolithotomy for the Treatment of Renal Stones Giray Ergin1*, Mustafa Kirac1, Burak Kopru1, Turgay Ebiloglu2, Hasan Biri1 Purpose: To compare the pain status and stone free rates of flexible ureterorenoscopy (F-URS) versus mini-per- cutaneous nephrolithotomy (mini-PNL) for the treatment of 1-to 2-cm renal stones. Materials and Methods: This study was retrospectively designed with match paired method. Between January 2013 and December 2016, 387 patients underwent stone surgery for renal stones, 45 patients underwent FURS and 45 patients underwent mini-PNL. 90 patients were divided into two groups according to the surgical procedures. Group 1 patients underwent F-URS, and Group 2 patients underwent mini-PNL. During the intraoperative and postoperative periods, pain management for all patients was standardized. Pain scores were determined using a visual analogue scale (VAS) completed at 2, 6, 12 and 24 hours postoperatively. The stone free status, hemoglobin levels, fluoroscopy time (FT), operation time (OT), hospitalization time (HT), return to work time (RWT), and complications were noted for each patient. Results: Of all patients, the mean age was 41.1 ± 12.1 years and the mean stone size was 13.9 ± 2.9 mm. The VAS scores were significantly higher in the mini-PNL group at 2, 6, 12 and 24 hours (P < .05). The stone-free status and complication rates were similar between the two groups (P > .05); however, the hemoglobin decreases and the fluoroscopy, operation, hospitalization and return to work times were higher in the mini-PNL group than in the F-URS group (P < .05). Conclusion: F-URS is less painful than mini-PNL for the treatment of 1- to 2-cm renal stones. However, the stone free rate is similar between the two procedures while mini-PNL is superior in terms of fluoroscopy, operation, hos- pitalization and return to work duration. We think that F-URS is more comfortable and less painful than mini-PNL and achieves a similar stone free rate for the treatment of 1- to 2-cm renal stones. Keywords: Flexible ureterorenoscopy; mini-percutaneous nephrolithotomy; stone treatment; urological surgery. INTRODUCTION Since the first placement of a percutaneous nephros-tomy tube for a hydronephrotic kidney in 1955(1), advancements in endourology have resulted in smaller devices for the percutaneous treatment of renal stones. In 1975, Harris et al. used a bronchoscope to treat renal stones(2), and in the following year, Fernstro ̈m and Jo- hansson defined the percutaneous pyelolithotomy tech- nique by using a nephrostomy tract(3). In 1998, Jackman et al. described the mini-percutaneous nephrolithtotomy (mini-PNL) technique using an 11-Fr vascular sheath for infants and preschool-aged children(4). Desai et al. then used the ultra-mini-PNL method in 2011, which had the least amount of access and utilized the 4.8-Fr microperc tract(5). Parallel to these advancements in per- cutaneous treatment methods, ureterorenoscopy tech- nology provided new approaches to renal stone therapy. In 1990, Fuchs et al. published the first report of a flexi- ble ureterorenoscopy (F-URS) procedure(6), after which F-URS became an alternative treatment option for renal stones together with improvements in laser and fiber technologies. The current EAU guidelines for urolithiasis recommend shock wave lithotripsy (SWL) as the initial treatment for renal stones smaller than 2 cm, except for the lower 1Koru Ankara Hospital, Department of Urology, Ankara, Turkey. 2Gulhane Training and Research Hospital, Department of Urology, Ankara, Turkey. *Correspondence: Koru Ankara Hospital, Department of Urology, Ankara, Turkey. Tel: +90 532 306 3959. Orchid Number: 0000-0003-2893-166X. drgirayergin@gmail.com. Received October 2017 & Accepted January 2018 pole stones with unfavorable risk factors (7). For stones larger than 2 cm, percutaneous nephrolithotomy (PNL) is recommended as the gold standard while cysteine stones, SWL refractory stones, or residual stones fol- lowing open surgery could be also treated with PNL. Miniperc (< 20 Fr) and ultra-mini-PNL, which use a smaller tract size, expanded the use of the PNL tech- nique for smaller stones in the area of SWL and led to comparable stone-free rates and fewer complications (8,9). For stones smaller than 2 cm, F-URS has recently gained increasing attention for its significantly lower risk of complications and sufficient stone-free rates. Stone-free rates > 80% have been reported for both the mini-PNL and F-URS techniques for renal stones larger than 10 mm(10). In this study, we investigated the effectiveness of the F-URS and mini-PNL techniques to determine which method is less invasive and painful while being more comfortable and suitable for renal stone treatment. MATERIALS AND METHODS Patients and grouping This study was retrospectively designed and approved by local ethic committee in our country. An Informed consent was obtained from all individual participants Endourology and Stone Diseases 313 Vol 15 No 06 November-December 2018 314 included in our study. Between January 2013 and De- cember 2016, 387 patients underwent surgery for renal stones. Of 387 patients, 90 were selected and match- paired according to age, stone size (1 to 2 cm) and stone localization. All patients were divided in two groups ac- cording to surgical procedures. Group 1 consisted of 45 patients who underwent FURS while group 2 consisted of 45 patients who underwent mini-PNL. The exclusion criteria were age < 18 years or > 65 years, morbid obe- sity, non-opaque renal stones, or anatomic abnormality. In preoperative period, all patients were evaluated by urinalysis, urine culture, hemoglobin (Hgb), serum urea and creatinine, coagulation tests and radiologic studies, including ultrasonography, radiography of the kidney, ureter, and bladder (KUB) and computerized tomog- raphy (CT). The stone sizes were determined by the longest axis of the stones in radiologic test. All patients received a single-dose intravenous prophylactic antibi- otic with a first-generation cephalosporin or quinolone during anesthesia induction. Mini-PNL technique A retrograde 5-Fr open-ended ureteral catheter was inserted into the patient under general anesthesia with 22-Fr cystoscope in the lithotomy position. A 16-Fr urethral catheter was inserted into the bladder for urine drainage. After ureteral catheter insertion, the patient was moved to a prone position with the appropriate pad- ding placed under the pressure points. The gonads were also protected from X-rays with gonad shields. Percu- taneous access was achieved under C-arm fluoroscop- ic (SIEMENS Arcadis Varic C-arm) guidance with an 18-gauge needle. A j-tipped curved guide wire (0.035 inch) was advanced to place the collecting system pref- erably in the upper calyx or ureter. The nephrostomy tract was dilated using Teflon Amplatz dilators (Cook Medical®) to establish an adequate tract size for the 14- Fr renal access sheath. A 10-Fr rigid nephroscope (Karl Storz, Berlin GmbH, Germany) was used for stone fragmentation and removal. The irrigation fluids were warmed to avoid hypothermia. Ultrasonic, pneumatic and laser lithotripsy were used for stone fragmentation. Laser lithotripsy was performed using a Holmium:yt- trium-aluminum-garnet laser (Dornier© MedTech Laser GmBH, Medilas H, h20-1518, Germany) through a re- usable 420 micron FlexiFib fiber (LISA Laser Products OHG). If necessary, the stone fragments were extracted using either grasping forceps or a zero-tip Nitinol stone basket. The operation was complete when no residual fragments could be detected by endoscopic and fluor- oscopic imaging. At the end of the procedure, a 10-Fr percutaneous ne- phrostomy (PCN) tube was inserted into the collection system. In some patients, the nephrostomy tube was not required. These patients had minimal or no bleeding, no collecting system or pelvic rupture, no stone fragmen- tation and no need for a secondary PNL procedure. A JJ stent was routinely placed for all patients. The ne- phrostomy tube was removed when the drainage was clear in the absence of fever or urine leakage around the tube. The JJ catheters were removed 2 weeks after the operation. F-URS technique Before flexible ureteroscopy, a 7.5-Fr rigid ureteros- copy (Karl-Storz, Germany) was performed in all pa- tients in the lithotomy position under general anesthesia to detect any previously unseen or nonopaque ureteral stones, place the safety guide-wire and dilate the ure- ter. All procedures were performed under visual (vid- eoscopic) and fluoroscopic guidance. Fluoroscopy was not routinely used. It was used when stent placement, access sheath insertion and necessary any reason. Af- ter the rigid ureteroscopy, a hydrophilic guide-wire was placed into the renal pelvis via rigid ureteroscope. A 9.5-11.5-Fr access sheath (UAS) (Boston Scientific®) was placed into the ureter, if possible. After ureteral ac- cess was obtained, a 7.5-Fr flexible ureteroscope (Karl Storz flex X2, Germany) was used for the stone treat- ment. The stones were fragmented with a holmium la- ser (Dornier© MedTech Laser GmBH, Medilas H, h20- 1518, Germany) using 170-200 µm laser fibers. The holmium laser was used at 0.6–1.2 J and 6–10 Hz. First, we tried to crush the stones into several fragments and then relocate them to the middle or upper calyx by stone basket so the lithotripsy could be performed easily. The stone fragments were extracted using a nitinol basket, if possible (NGage® Nitinol Stone Extractor). At the end of the procedure, a JJ catheter was inserted if there was ureteral injury, ureteral or pelvic edema, an extended operation time or excessive passing of the ureteroscope for renal access. The JJ catheters were removed under brief anesthesia 2 weeks after the operation. Pain management The pain management for all patients was standardized. After the operation, all patients received a single dose of intravenous meperidine hydrochloride (pethidin) 1 mg/kg from the anesthesiologist in the operation room. During the postoperative period, 50 mg intramuscular dexketoprofen trometamol and 50 mg intramuscular meperidine hydrochloride were used for pain manage- ment. These drugs were used at request of the patients (dexketoprofen trometamol max 150 mg/day and me- peridine hydrochloride max 100 mg/day). Meperidine hydrochloride was used only on postoperative day 1. During the following postoperative days, pain was man- aged with 25 mg dexketoprofen hydrochloride taken orally twice per day. Each analgesic request was noted. Follow-up During the postoperative period, pain scoring was as- sessed using a visual analog scale (VAS)(11). In our clinic, we routinely perform the VAS measurements in post-operative period. The VAS was used to classi- fy pain severity among ten 1-cm horizontal segments, with no pain indicated at 0 cm and the worst pain at 10 cm. The VASs were completed at 2, 6, 12 and 24 hours postoperatively. The fluoroscopy time (FT), operation time (OT), JJ stent insertion rates, hospitalization time (HT) and return to work time (RWT) were also noted. Complications were classified according to the Clavien Classification system(12). On the first postoperative day, patients’ general condition and pain status were eval- uated, and KUB was performed to verify the JJ stent insertion and stone-free status. During the first post- operative month, low dose computed tomography was performed. Stone-free status was defined as no residual fragments on CT evaluation during the first postopera- tive month. Residual stones ≤4 mm in size were defined as clinically insignificant residual fragment (CIRF)(13). After obtaining approval of the local ethics committee, we retrospectively assessed the patients’ files and docu- ments in our clinics. An inform consent form including Flexible URS Versus Mini-PCNL in terms of pain.-Ergin et al. ethical and detailed surgical procedure was given to all patients before the surgery. Statistical Analysis Statistical analysis was done using Statistical Pack- age for Social Sciences 20.0 software (SPSS 20.0 for MAC). Descriptive statistics of nominal samples were expressed with numbers and percentiles. Descriptive statistics of scale samples were expressed as mean ± standard deviation (minimum-maximum). Shap- iro-Wilk, Kurtosis, and Skewness Tests were used to assess the variables’ normalization. The Independent Sample T Test was used to compare the pre and post procedure independent scale parameters with normal- ly distribution. The Mann-Whitney U Test was used to compare the pre and post procedure independent scale parameters without normally distribution. The Paired Sample T Test was used to compare the pre and post procedure dependent scale parameters with normal distribution. The Wilcoxon Test was used to compare the pre and post procedure dependent scale parameters without normal distribution. Mc Nemar Test was used to compare the pre and post procedure dependent nom- inal parameters. Chi Square Test was used to compare the pre and post procedure independent nominal param- eters. ANOVA test was used to compare the repeated scale parameters with normal distribution. Friedman Test was used to compare the repeated scale parameters without normal distribution. Probability of p < 0.05 was accepted as statistically significant. RESULTS The demographic data and preoperative parameters of all patients are shown in Table 1. The demographic characteristics were similar between the groups (P < .05). The mean stone size was 13.7 ± 2.5 mm and 14.2 ± 3.3 mm in the group 1 and group 2, respectively (P = .251). After 1 month stone-free rates were similar between groups, but the hemoglobin decreases, FT, OT, HT and RWT were higher in the group 2 (P = .023, .002, .004, .001, and .001, respectively). The perioperative and postoperative parameters are reported in Table 2. The mean VAS scores were significantly higher in the group 2 at 2, 6, 12 and 24 hours (P < .05). The mean VAS for all patients are shown in Table 3. During the study period, there was no any major com- plication. Clavien grade 1 complication were detected in two patients in group 1 and three patients in group 2. In group 2, 1 patient have a Clavien 2 complication such as received transfusions. There was no statistically significant result in two groups in terms of complication rate (CR) (P = .054) In the post-operative period, total meperidine hydro- chloride requirements were not different in two groups, however, amount of dexketoprofen trometamol needed were significantly less in group 1 (P = .001) (Table 2). Table 1. Preoperative Data of All Patients Demographic Data F-URS Mini-PNL p value The mean age ± SD mean ±S D 40.46 ± 12.4 41.93 ± 11.9 0.137 The mean Stone Size (mm) mean ± SD 13.7 ± 2.5 14.2 ± 3.3 0.251 Gender (male/female) 31/14 29/16 0.421 Side of Surgery (left/right) 22/23 24/21 0.812 Location of stone (%) 0.632 Upper Pole 10 (22.2) 11 (24.5) - Middle Pole 19 (42.2) 16 (35.5) - Lower Pole 16 (35.6) 18 (40.0) - Abbreviations: F-URS, Flexible Ureterorenoscopy; Mini-PNL, Mini-Percutaneous Nephrolithotomy; SD, Standard deviation Data F-URS Mini-PNL p value Fluoroscopy Time (sec.) mean ± SD 3.1 ± 0.9 123 ± 14.3 0.002 Operation time (min.) mean ± SD 37.5 ± 6.6 57.3 ± 7.5 0.004 Hemoglobin Drop (mg/dl) 0.44 2.15 0.023 Complications rate (%) 0.054 Clavien 1 2 (4.4) 3 (6.6) - Clavien 2 - 1 (2.2) - Clavien 3 - - - Clavien 4 - - - JJ stent insertion rate (%) 45 (100.0) 45 (100.0) - Nephrostomy tube insertion rate (%) 0 (0.0) 37 (82.2) - Mean Hospitalization Time (hour) mean ± SD 16.8 ± 3.2 43.9 ± 8.6 0.001 Stone-free rate (1. month) 40/45 (88.8) 42 (93.3) 0.453 CIRF rate (%) 2/45 (4.4) 1/45 (2.2) Return to Work Time (day) mean ± SD 2.53 ±1.0 8.93 ± 2.2 0.001 The total mean analgesic requirement’s Meperidine hydrochloride (mg) mean ± SD 76.5±14.3 78.7 ± 15.2 0.15 Dexketoprofen trometamol (mg) mean ± SD 166.0±45.4 214 ± 39.5 0.001 Abbreviations: F-URS, Flexible Ureterorenoscopy; Mini-PNL, Mini-Percutaneous Nephrolithotomy; CIRF, Clinical insignificant Re- sidual Stone; sec, Second; min, Minute Table 2. Preoperative and Postoperative Parameters of All Patients Flexible URS Versus Mini-PCNL in terms of pain.-Ergin et al. Endourology and Stone Diseases 315 Vol 15 No 06 November-December 2018 316 DISCUSSION Managing renal stone disease with the highest possible success rate in a single setting is the aim of all endourol- ogists worldwide. For this purpose, we reported our re- sults in an effort to reach a consensus about the best method for a urinary system stone. However, what is the real measure of success after stone disease surgery: is it the stone-free rate, the cost, the resolution of pain, or the complication rate? Following the invention of the mini-PNL method, many investigators reported less hemorrhage, less analgesia and reduced hospitalization time(12-14). In addition, use of the mini-PNL approach achieved a similar stone- free rate and no major complications compared with PNL(14,15). For the stones < 2 cm, another technique named F-URS was first described by Fuchs et al(6). and was speculated to have even lower complication rates than mini-PNL. Following the developments in laser and flexible endo- scopic technologies, F-URS is also an acceptable treat- ment method for larger kidney stones (10-20 mm in size). According to the 2016 guidelines of the European Association of Urology, F-URS is third-line treatment option for 10-20 mm kidney stones (7) . Moreover, some recent reports have suggested F-URS for stones >2 cm with lower complication rates than those observed for the gold standard treatment modality, PNL(16). In the terms of stone-free rates (SFR), Kruck et al. encour- aged the use of mini-PNL or F-URS rather than SWL for stones > 1 cm. They reported that mini-PNL, F-URS and SWL had 77.3%, 72.7%, and 14.8% SFRs for lower pole stones and 80.4%, 69.2%, and 39.3% for non-low- er pole stones, respectively (17). A multicenter study reported 83.6%, 86.1%, and 77.2% SFRs in mini-PNL, F-URS, and SWL, respectively(18). In another prospec- tive study, mini-PNL and F-URS were reported to have 100% and 96.88% SFRs, respectively (19). Akbulut et al. reported 85.7% and 90.3% SFRs for mini-PNL and F-URS, respectively(20). Schoenthaler et al. used the 14-Fr dilatation, as in our study, and reported 84% and 87% SFRs for the ultra-mini-PNL and F-URS groups, respectively(21). Ozgur et al. compared the miniaturized PNL (with 20-F dilatation and a 17-F nephroscope) and F-URS in obese patients and reported 80.4% and 76.7% SFRs, respectively(22). According to these studies, al- though mini-PNL seems to be superior to F-URS, no studies have reported a statistically significant differ- ence between the techniques. In a meta-analysis by Gao XS and colleagues, it was reported that stone-free rates of mini-PNL were higher than RIRS(23).They reported that in the meta-analysis mini-PNL provided a signif- icantly higher stone free rate, especially for lover pole renal stones. In our study, we found 93.3 % and 88.8 % SFRs in the mini-PNL and F-URS groups on the first postoperative month. These results are not significantly different from each other, and our SFR results are sim- ilar to those obtained in most studies in the literature. At the 3-month follow up, there was only 1 patient in each group with significant residual stones (SRS), and a second F-URS made these patients stone-free. In the study by Lee et al., the mean VAS scores at 1 hour and 1 day postoperatively in the mini-PNL and F-URS groups were reported to be 4.2 and 5.7 and 2.7 and 3.1, respectively. Within the first postoperative hour, mini-PNL caused significantly lower pain than did F-URS, but at postoperative day 1, there was no dif- ference(10). In the study by Sabnis et al., F-URS report- edly caused less pain than mini-PNL did at 6, 24, and 48 hours postoperatively(19). In our research, F-URS caused less pain at 2, 6, 12, and 24 hours postoperatively. In our study, Hgb decrease, OT and FT were reported to be less in the F-URS group than in the mini-PNL group. The complication rates were not different between the groups. According to Gao XS and their colleagues’ me- ta-analysis, Hgb decrease and hospitalization time were longer in mini-PNL group. They reported that OT and complication rates were no statistical differences be- tween mini-PNL and F-URS(23). Pan et al. reported the mean OT to be 73.07 ± 13.5 and 62.39 ± 10.6 min in the F-URS and mini-PNL groups, respectively(24). Contrary to the results from the studies above, Akbulut et al. re- ported a shorter OT but similar Hgb decreases and FT for F-URS (20). In our study, we found significantly less Hgb decreases and shorter FT and OT, thus favoring the use of F-URS. The diminished field visibility and the need for prolonged lithotripsy to obtain small frag- ments suitable for extraction through the small sheath were the major factors for the long operative time in the mini-PNL group. The CRs were not significantly different between the groups, but 1 patients did require blood transfusions (Clavien 2) in the mini-PNL group. Hospitalization time (HT) and return to work time (RWT) are the other hints as to the usefulness of these techniques. Kıraç and Akbulut et al. reported a shorter HT for F-URS(20,25). Schoenthaler et al. reported a HT of 2.3 and 2.0 days for ultra-mini-PNL and F-URS groups, respectively(21). Ozgor et al. reported HTs of 22.4 and 63.8 hours for miniaturized PNL and F-URS groups, respectively(22). Our research supports the previous studies. In our study, we found significantly lower HT in F-URS group. However, we think that RWT is more important than HT for selecting a technique for 1-2 cm stones. With this in mind, we examined the RWT and determined that F-URS was a more useful technique than mini-PNL. Our study has some limitations. Patient size is the main limitation. Additionally, the retrospective and multi- center nature of the study is another limitation. Studies with more patients in a single center will reveal better results about this subject. CONCLUSIONS F-URS and mini-PNL are effective treatment modali- ties for 1- to 2-cm renal stones with a similar stone-free rate. F-URS is less painful compared with mini-PNL We concluded that F-URS results in shorter hospitali- zation and return to work times than mini-PNL. Further studies are needed to confirm these results. Table 3. The mean VAS of patients during the postoperative pe- riod Postoperative period F-URS Mini-PNL p value 2. hours mean ± SD 1.8 ± 0.3 6.3 ± 1.1 0.001 6. hours mean ± SD 1.9 ± 0.3 5.0 ± 1.2 0.001 12. hours mean ± SD 1.1 ± 0.2 4.1 ± 0.6 0.002 24. hours mean ± SD 0.6 ± 0.1 2.5 ± 0.8 0.001 Abbreviations: F-URS, Flexible Ureterorenoscopy; Mini-PNL, Mini-Percutaneous Nephrolithotomy Flexible URS Versus Mini-PCNL in terms of pain.-Ergin et al. CONFLICT OF INTEREST The authors report no conflict of interest. REFERENCES 1. Goodwin WE, Casey WC, Woolf W. Percutaneous trocar (needle) nephrostomy in hydronephrosis. J Am Med Assoc. 1955;157:891-4. 2. Harris RD, McLaughlin AP, 3rd, Harrell JH. Percutaneous nephroscopy using fiberoptic bronchoscope: removal of renal calculus. Urology. 1975;6:367-9. 3. Fernstrom I, Johansson B. Percutaneous pyelolithotomy. A new extraction technique. Scand J Urol Nephrol. 1976;10:257-9. 4. Jackman SV, Hedican SP, Peters CA, Docimo SG. Percutaneous nephrolithotomy in infants and preschool age children: experience with a new technique. Urology. 1998;52:697-701. 5. Desai J, Solanki R. Ultra-mini percutaneous nephrolithotomy (UMP): one more armamentarium. BJU Int. 2013;112:1046-9. 6. Fuchs GJ, Fuchs AM. [Flexible endoscopy of the upper urinary tract. A new minimally invasive method for diagnosis and treatment]. Urologe A. 1990;29:313-20. 7. Turk C, Petrik A, Sarica K, et al. EAU Guidelines on Diagnosis and Conservative Management of Urolithiasis. Eur Urol. 2016;69:468-74. 8. Cheng F, Yu W, Zhang X, Yang S, Xia Y, Ruan Y. Minimally invasive tract in percutaneous nephrolithotomy for renal stones. J Endourol. 2010;24:1579-82. 9. Desai MR, Sharma R, Mishra S, Sabnis RB, Stief C, Bader M. Single-step percutaneous nephrolithotomy (microperc): the initial clinical report. J Urol. 2011;186:140-5. 10. Lee JW, Park J, Lee SB, Son H, Cho SY, Jeong H. Mini-percutaneous Nephrolithotomy vs Retrograde Intrarenal Surgery for Renal Stones Larger Than 10 mm: A Prospective Randomized Controlled Trial. Urology. 2015;86:873-7. 11. Bijur PE, Silver W, Gallagher EJ. Reliability of the visual analog scale for measurement of acute pain. Acad Emerg Med. 2001;8:1153-7. 12. Dindo D, Demartines N, Clavien PA. Classification of surgical complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg. 2004;240:205-13. 13. Newman DM, Lingeman JE. Management of upper urinary tract calculi with extracorporeal shock-wave lithotripsy. Compr Ther. 1989;15:35-40. 14. Mishra S, Sharma R, Garg C, Kurien A, Sabnis R, Desai M. Prospective comparative study of miniperc and standard PNL for treatment of 1 to 2 cm size renal stone. BJU Flexible URS Versus Mini-PCNL in terms of pain.-Ergin et al. Int. 2011;108:896-9; discussion 9-900. 15. Nagele U, Schilling D, Anastasiadis AG, et al. [Minimally invasive percutaneous nephrolitholapaxy (MIP)]. Urologe A. 2008;47:1066, 8-73. 16. Hyams ES, Munver R, Bird VG, Uberoi J, Shah O. Flexible ureterorenoscopy and holmium laser lithotripsy for the management of renal stone burdens that measure 2 to 3 cm: a multi-institutional experience. J Endourol. 2010;24:1583-8. 17. Kruck S, Anastasiadis AG, Herrmann TR, et al. Minimally invasive percutaneous nephrolithotomy: an alternative to retrograde intrarenal surgery and shockwave lithotripsy. World J Urol. 2013;31:1555-61. 18. Kiremit MC, Guven S, Sarica K, et al. Contemporary Management of Medium-Sized (10-20 mm) Renal Stones: A Retrospective Multicenter Observational Study. J Endourol. 2015;29:838-43. 19. Sabnis RB, Jagtap J, Mishra S, Desai M. Treating renal calculi 1-2 cm in diameter with minipercutaneous or retrograde intrarenal surgery: a prospective comparative study. BJU Int. 2012;110:E346-9. 20. Akbulut F, Kucuktopcu O, Kandemir E, et al. Comparison of flexible ureterorenoscopy and mini-percutaneous nephrolithotomy in treatment of lower calyceal stones smaller than 2 cm. Ren Fail. 2016;38:163-7. 21. Schoenthaler M, Wilhelm K, Hein S, et al. Ultra-mini PCNL versus flexible ureteroscopy: a matched analysis of treatment costs (endoscopes and disposables) in patients with renal stones 10-20 mm. World J Urol. 2015;33:1601-5. 22. Ozgor F, Tepeler A, Elbir F, et al. Comparison of miniaturized percutaneous nephrolithotomy and flexible ureterorenoscopy for the management of 10-20 mm renal stones in obese patients. World J Urol. 2015. 23. Gao XS, Liao BH, Chen YT, et al. Different Tract Sizes of Miniaturized Percutaneous Nephrolithotomy Versus Retrograde Intrarenal Surgery: A Systematic Review and Meta-Analysis. J Endourol. 2017;31:1101-10. 24. Pan J, Chen Q, Xue W, et al. RIRS versus mPCNL for single renal stone of 2-3 cm: clinical outcome and cost-effective analysis in Chinese medical setting. Urolithiasis. 2013;41:73-8. 25. Kirac M, Bozkurt OF, Tunc L, Guneri C, Unsal A, Biri H. Comparison of retrograde intrarenal surgery and mini-percutaneous nephrolithotomy in management of lower- pole renal stones with a diameter of smaller than 15 mm. Urolithiasis. 2013;41:241-6. Endourology and Stone Diseases 317