Archivio Italiano di Urologia e Andrologia 2017; 89, 3226 ORIGINAL PAPER Renal access in PNL under sonographic guidance: Do we really need to insert an open end ureteral catheter in dilated renal systems? A prospective randomized study Bilal Eryildirim, Murat Tuncer, Emre Camur, Fatih Ustun, Fatih Tarhan, Kemal Sarica Dr. Lütfi Kirdar Training and Research Hospital Urology Clinic, Istanbul, Turkey. Purpose: To evaluate the true necessity of open end ureteral catheter insertion in patients with moderate to severe pelvicalyceal system dilation treated with percutaneous nephrolithotomy (PNL) under sono- graphic guidance. Patients and methods: 50 cases treated with PNL under sono- graphic guidance in prone position for solitary obstructing renal stones were evaluated. Patients were randomly divided into two groups; Group 1: Patients in whom a open end ureter- al catheter was inserted prior to the procedure; Group 2: Patients receiving no catheter before PNL. In addition to the duration of the procedure as a whole and also all relevant stages as well, radiation exposure time, hospitalization period, mean nephrostomy tube duration, mean drop in Hb levels and all intra and postoperative complications have been evaluated. Results: Mean size of the stones was 308.5 ± 133.2 mm2. Mean total duration of the PNL procedure in cases with open end ureteral catheter was significantly longer than the other cases (p < 0.001). Evaluation of the outcomes of the PNL procedures revealed no statistically significant difference between two groups regarding the stone-free rates (86% vs 84%). Additionally, there was no significant difference with respect to the duration of nephrostomy tube, hospitalization period and secondary procedures needed, complication rates as well as the post-operative Hb drop levels in both groups (p = 0.6830). Conclusions: Our results indicate that the placement of an open end ureteral catheter prior to a PNL procedure per- formed under sonographic access may not be indicated in selected cases presenting with solitary obstructing renal pelvic and/or calyceal stones. KEY WORDS: Percutaneous nephrolithotomy; Ureteral catheter; Renal stone; Ultrasonographic access. Submitted 12 July 2017; Accepted 7 August 2017 Summary No conflict of interest declared. oroscopic and/or ultrasonographic guidance. Although fluoroscopic guidance has been used as the most common method for a long period of time, increasing experience in sonographic applications has enabled endourologists to use this method more commonly than ever to get an access to the renal collecting system. Use of sonography will allow the surgeon to identify the pelvicalyceal system as well as the surrounding organs in a safe manner (particu- larly in relatively dilated systems) to reduce the radiation exposure in a meaningful manner (10, 11). On the other hand, an open end ureteral catheter has been commonly used during percutaneous stone removal procedures to visualise the renal collecting system, avoiding the passage of small stone fragments into the ureteric lumen and lastly but most importantly to dilate the renal collecting system to ease the puncture when needed. Despite all these well- established advantages however, insertion of an “open end ureteral catheter” may certainly be associated with some possible problems. First of all, a certain injury to the ure- thra particularly in male cases as well as to the mucosa of the relevant ureter could be caused. Additionally, loss of time due to the insertion of the catheter first in supine position and turning of the case into prone position will further prolong the duration of the procedure (the dura- tion of the anesthesia as well). Thus, in the light of the safe and practical renal puncture in a quick manner in dilated kidneys as well as the problems related to the placement of a catheter use of an open end ureteral catheter in all cases becomes really questionable. In this present study we aimed to evaluate the true neces- sity of open end ureteral catheter insertion prior to PNL for a succesful procedure as well as the safety of renal punc- ture performed under sonographic guidance in patients with pelvicalyceal system dilation (Grade 2 or higher) by comparing two group of cases treated with and without insertion of an open end ureteral catheter before PNL. PATIENTS AND METHODS Study population Between January 2015 and January 2017, of all the 236 cases undergoing PNL, procedure in our department, 72 patients meeting the inclusion criteria were included into study program and randomized. Upon randomization DOI: 10.4081/aiua.2017.3.226 INTRODUCTION Following its first application in 1976, percutaneous nephrolithotomy (PNL) technique has evolved substan- tially over the last three decades and became the preferred choice in the management of larger stones (> 2 cm) both in adults and children (1-3). Although the procedure is safe and successful with stone-free rates of > 90 %, certain complications may develop during all stages as well as early and late follow-up period of this procedure (4-9). Related to this subject, an appropriate initial puncture of the most desirable calyx of the kidney is of paramount importance and access can be established either under flu- Eryildirim _Stesura Seveso 28/09/17 10:27 Pagina 226 227Archivio Italiano di Urologia e Andrologia 2017; 89, 3 Do we really need ureteral catheter in dilated systems during PNL? while 27 cases in Group 1 and 28 cases in Group 2 were operated with PNL technique, cases who were not operat- ed due to some certain reasons were excluded from the study program. Moreover, 2 cases in Group 1 and 3 cases in Group 2 were lost to follow-up for several reasons and finally 50 cases (31 males, 19 females) were analyzed. Patients’ enrollment algorithm has been illustrated in Figure 1. In an attempt to assess the sample size, power analysis was made by using G*Power (v3.1.7) program. Depending on the index of effect size of Cohen; suppos- ing that the evaluations between two independent groups will have the highest effect size (d = 0.85), our calculations did show that at least 23 cases should be included into each group. Additionally, taking the possi- bility of patient drop-out risk during the study program, final number of the cases in each group has been pro- posed to be 25. While cases presenting with pelvicalyceal system dilation (Grade 2 or higher) due to moderate sized solitary renal pelvic and/or calyceal stones were included into the study program, all other cases with a detectable patholo- gy with respect to the integrity of the ureter prior to the PNL were excluded from the study program. Patients with renal anomalies, non-dilated renal collect- ing systems and younger than 18 years of age were also excluded from the study program. Study design This study is a prospective single center, randomized clinical trial with balanced randomization [1:1] which was performed in the referral hospital Dr. Lutfi Kirdar Kartal Training and Research Hospital. For randomization procedure a simple randomization method by generating a random digit (0-60 in each group) has been used. Even numbers have been used for cases in whom an open end ureteral catheter was inserted and odd numbers have been used for cases whom operated without an open end ureteral catheter. Study protocol was approved by the Ethics Committee of the relevant hospital (September 08, 2016-2016/514/91/3). All steps of the study were planned and applied carefully according to Helsinki Declaration. All PNL procedures were performed in prone position by experienced urologists and access to the renal collecting system was performed under sonographic guidance. Depending on the placement of an open end ureteral catheter, the patients were divided into two different groups namely; Group 1: Patients in whom a 5 French (F) open end ureteral catheter was inserted prior to the procedure; Group 2: Patients not receiving an open end ureteral catheter insertion before PNL. Following a complete biochemical and radiological eval- uation; patients with urinary tract infections were treat- ed with appropriate culture test based antibiotics. Regarding the radiological evaluation, ultrasonography (USG), kidney-ureter-bladder (KUB) film and low-dose computed tomography (CT) have been performed to assess the renal anatomy, degree of hydronephrosis, position of the relevant kid- ney with neighboring organs and location, burden of the stone(s) to be treated. Stone area has been calculated by using the two dimensions of the stone(s) from CT images. While the primary outcome of our study was to evaluate and compare the ultimate stone free rates after both approaches¸ secondary end points were the evaluation of operational duration, com- plication rates, mean fluo- roscopy time and hospital stay period in both groups in a comparative manner. Figure 1. CONSORT Flow Diagram of study. Eryildirim _Stesura Seveso 28/09/17 10:27 Pagina 227 Archivio Italiano di Urologia e Andrologia 2017; 89, 3 B. Eryildirim, M. Tuncer, E. Camur, F. Ustun, F. Tarhan, K. Sarica 228 Surgical technique of PNL procedure Following general anesthesia, while performing cys- toscopy, a 5 F open end ureteral catheter was placed into the relevant ureter till ureteropelvic junction area in Group 1 cases in the lithotomy position, no open end ureteral catheter was inserted in Group 2 cases and a prone position has been given directly in these cases. An appropriate calyceal puncture under full sonographic guidance was done with a 18 gauge percutaneous entrance needle (Boston Scientific, Natick, MA, USA). Following puncture of the kidney, a 0.038 inch guide wire was inserted into the collecting system (into the ureter when possible) and Amplatz mechanical dilata- tors were used for percutaneous tract dilatation (Amplatz sheath, Boston Scientific, Natick, MA, USA) until 28-30 F. Following the placement of an appropriate access sheath a standard 26 F nephroscope (Karl Storz, Tuttlingen, Germany) was placed directly into the kidney through the tract and the stone disintegrated using an ultrasonic lithotripsy probe (Swiss Lithoclast®, EMS Electro Medical System, Nyon, Switzerland). Fragments were removed by suction, tipless basket, or grasping forceps. At the end of the procedures, a re-entry nephrostomy catheter (14 F) was placed, and an ante- grade pyelography was performed to check for possible complications in all cases. The open end ureteral catheter was removed at the end of the operation in Group 1 cases. The nephrostomy tube was removed postoperatively on the first or second day as soon as the urine became clear. Outcome assessment All patients were re-evaluated by a plain abdominal film and/or sonography after 24 hours and by a non-contrast abdominal tomography at the end of a 4 weeks period. The operation was considered successful if there were no fragments at all or if the size of the residual fragments were smaller than 4 mm. In addition to the duration of the procedure as a whole and also all relevant stages as well, the duration of radi- ation exposure, hospitalization period along with the mean duration of nephrostomy tube, mean drop in hemoglobin (Hb) levels, all intraoperative, and postopera- tive complications have been evaluated and recorded. Statistical analysis The Prism 5.0 (GraphPad Software, San Diego, CA) was used for the statistical analy- sis. Data are presented as mean standard deviation of mean. Mann Whitney U test was used for both compari- son of descriptive statistical methods and evaluation of quantitative data and Fisher exact test were used to com- pare the qualitative data between two groups, a two- sided p < 0.05 was consid- ered statistically significant. RESULTS A total of 50 cases (31 males/19 females M/F: 1.63) were treated with standard PNL for moderate sized solitary calyceal or pelvic stones and sonographic guidance was used for renal puncture. While the age of the cases ranged from 22-72 years (mean 44.90 +/- 12.32 years, 95% CI: 41.00-48.40), the mean size of the treated stones was 308.5 +/-133.2 mm2, (95% CI: 270.7-346.4). Demographic as well as radiologic characteristics of the cases are given in Table 1. The stones were located in the calyceal system in 28 cases (6 cases upper, 9 cases mid- dle, 13 cases lower calyx) and in the renal pelvis in 22 cases. There was no significant difference regarding the size of the stones in both groups. Evaluation of our findings in both groups revealed fol- lowing data. Regarding the duration of the treatment as a whole or in certain parts of the procedure, our results show clearly that the mean total duration of the PNL procedure in cases with open end ureteral catheter was significantly longer than the other cases (85.80 +/- 16.18 vs 60.84 +/- 13.21 minute respectively, p < 0.001). The mean duration for an open end ureteral catheter insertion in Group 1 was 27.96 +/- 5.86, (95% CI: 25.54-30.38) min. and this time peri- od was the main cause for prolonged total operative time in these cases. On the other hand however, there was no statistically significant difference with respect to the mean duration of other isolated stages of PNL procedure (renal puncture, access sheath placement, stone disintegration and removal) as shown in Table 2. As an important parameter again, although the mean fluo- roscopic exposure time was relatively longer in cases treat- ed with an open end ureteral catheter, this difference was not statistically significant (p = 0.3595). Evaluation of the outcomes of the PNL procedures in terms of success rates as well as early post-operative follow-up data revealed no statistically significant difference between the two groups regarding the stone-free rates (84 % vs 88 %) and also the percentage of the cases with residual fragments sizing > 4 mm (p = 1.00) (Table 3). Additionally, when we evaluated the cases with respect to the duration of nephrostomy tube, hospitalization period and secondary procedures needed Double J stent placement and ureteroscopy (URS) again we were not able to show any significant difference in these Table 1. Evaluation of patient and stone characteristics in both groups. Variablesa Overall Group 1 Group 2 P value n = 50 Ureteral catheter (+) Ureteral catheter (-) n = 25 n = 25 Age, year; mean ± SD 44.90 12.32 47.00 11.05 42.80 13.36 0.2175 (range) (22-72) (26-60) (22-72) BMI, kg/m2; mean ± SD 27.18 4.14 28.52 4.20 25.84 3.69 0.0380 (range) (18.2-38.0) (22.3-38.0) (18.2-34.5) Stone burden, mm2; mean ± SD 308.5 133.2 297.8 106.5 319.2 157.0 0.7784 (range) (195-570) (195-570) (200-530) HU, Hounsfield unit; mean ± SD 812 198.3 766.3 164.5 857.5 202.4 0.1276 (range) (450-1500) (450-1480) (470-1500) Degree of hydronephrosis, Grade; mean ± SD 2.22 0.50 2.16 0.47 2.28 0.54 0.3024 (range) (2-4) (2-4) (2-4) BMI: Body mass index; HU: Hounsfield unit. a Continuous variables were compared by Mann Whitney U test. Eryildirim _Stesura Seveso 28/09/17 10:27 Pagina 228 229Archivio Italiano di Urologia e Andrologia 2017; 89, 3 Do we really need ureteral catheter in dilated systems during PNL? values. Last but not least as another important parameter to be evaluated, there was also no notable difference regarding the post-operative drop in Hb levels in both groups (p = 0.6830). Finally, evaluation of the complications in the light of modified Clavien grading system demonstrated no statisti- cally significant difference between the two groups partic- ularly concerning bleeding after PNL (Table 4). As sum- marized in this table, while one case in each group required double J stent insertion due to the prolonged urine leakage after nephrostomy tube removal, a stone passing into the ureter despite open end ureteral catheter placement was removed with URS in one case of Group 1. Relocation of the disintegrated stone fragments down into the ureteric lumen could be a significant drawback of this approach however, as we tend to remove all relatively larger fragments during the proce- dure with great care, there will be very limited chance for fragment relocation in these cases with moderate sized cal- culi. Moreover, it is clear that passage of the fragments down into the ureteric lumen might occur despite given care and open end ureteral catheter insertion (like the case in Group 1 of our study) in a cer- tain percentage of the cases. DISCUSSION Percutaneous nephrolithotomy has been performed as a minimally invasive method of removing kidney stones since 1976. As a result of the improvements in operative technique and miniaturization of the available equipment, this approach is now commonly performed as a safe and successful management option in larger stones. However, despite the high stone free rates obtained in a single ses- sion; PNL could be associated with certain types of com- plications like bleeding, organ perforation and sepsis (12). Such complications could be encountered during all steps of PNL among which the access to the renal collecting sys- tem seems to be the most important one (13). Related to this subject, an appropriate initial puncture of the most desirable calyx of the kidney is extremely important for a successful and safe proce- dure by limiting the chance of both bleeding as well as injury to the surrounding organs (e.g. colon, spleen, liver, pleura, lung). Access to the renal col- lecting system from the most suitable calyx can be estab- lished either under fluoroscop- ic and/or sonographic guid- ance. Main aim of these two different guiding procedures should be a direct path which will be identified and used from the skin through the papilla of the desired calyx (14). Accumulated experience so far has clearly demonstrated that each of these methods could be associated with cer- tain advantages as well as dis- advantages. Related to this sub- ject, during fluoroscopic guid- ance renal puncture is usually done after the placement of an open end ureteral catheter through cystoscopy. Use of this catheter will in turn allow the Table 4. Evaluation of the type and grade of complications according to modified Clavien classification in both groups. Grade Complication Overall Group 1 Group 2 b P value n = 50 Ureteral Ureteral catheter (+) catheter (-) n = 25 n = 25 1 Fever > 38 0C; n, (%) 5 (10.0) 3 (12.0) 2 (8.0) 1.0000 Hemorrhage not requiring blood transfusion; n, (%) 4 (8.0) 2 (8.0) 2 (8.0) 2 Hemorrhage requiring blood transfusion; n, (%) 2 (4.0) 1 (4.0) 1 (4.0) 1.0000 3a Double J stent placement for urine leakage > 24 h; n, (%) 2 (4.0) 1 (4.0) 1 (4.0) 1.0000 3b Endoscopic treatment for ureteral stone; n, (%) 1 (2.0) 1 (4.0) - 1.0000 a Continuous variables were compared by Mann Whitney U test. b Continuous variables were compared by Fisher exact test. Table 3. Evaluation of the outcomes of the procedures in terms of success rates as well as early post-operative follow-up data. Variablesa, b Overall Group 1 Group 2 P value n = 50 Ureteral catheter (+) Ureteral catheter (-) n = 25 n = 25 b Stone free rate; n, (%) 43 (86.0) 21 (84.0) 22 (88.0) 1.0000 b Residual stone > 4 mm n, (%) 7 (14.0) 4 (16.0) 3 (12.0) 1.0000 a Mean drop in hb levels (g/dL) 1.52 0.68 1.60 0.69 1.45 0.57 0.6830 a Mean duration of nephrostomy (day) 1.86 0.88 1.83 0.79 1.92 0.92 0.7246 a Mean hospital stay (day) 2.88 0.96 2.84 0.96 2.92 1.03 0.9010 b Secondary intervention; n, (%) 3 (6.0) 2 (8.0) 1 (4.0) 1.0000 a Continuous variables were compared by Mann Whitney U test. b Continuous variables were compared by Fisher exact test. Table 2. Evaluation of the procedure related parameters with an emphasis on the duration of the interventional steps in both groups. Variablesa Overall Group 1 Group 2 P value n = 50 Ureteral catheter (+) Ureteral catheter (-) n = 25 n = 25 Mean duration of the procedure (min) 73.12 18.90 85.80 16.18 60.84 13.21 < 0.0001 Mean duration of open end catheter insertion (min) - 27.96 5.86 - - Mean duration of access to the collecting system (min) 5.42 2.32 5.28 2.08 5.76 2.45 0.4909 Mean duration of dilation and access sheath placement (min) 10.34 3.96 10.08 3.22 10.67 4.02 0.5118 Mean duration of fragmentation and stone removal (min) 27.38 12.53 25.96 11.80 28.80 12.86 0.3896 Mean fluoroscopy time (sec.) 18.20 9.60 19.60 11.08 17.36 7.63 0.3595 a Continuous variables were compared by Mann Whitney U test. Eryildirim _Stesura Seveso 28/09/17 10:27 Pagina 229 Archivio Italiano di Urologia e Andrologia 2017; 89, 3 B. Eryildirim, M. Tuncer, E. Camur, F. Ustun, F. Tarhan, K. Sarica 230 surgeon to dilate the collecting system with saline injection for an easy puncture particularly in cases with minimal or no dilation and also to visualize the pelvicalyceal system with contrast medium. To accomplish this task however, patients are initially placed into a lithotomy position for the placement of the ureteral catheter and then brought into the prone position to perform the kidney puncture and access to the renal collecting system. It is clear that these procedures and maneuvers will certainly lengthen the total operational time for these cases being operated under gen- eral anesthesia. Additionally and more importantly a cer- tain injury to the urethra particularly in male cases as well as to the mucosa of the relevant ureter could be caused. On the other hand again, the administration of contrast agent may cause severe, contrast-related complications and the contrast agent may affect the opacity of the stone, causing challenges for the endourologist during stone manipulation. Moreover, the fear of injuring struc- tures during a ‘blind’ approach under fluoroscopic guid- ance up to the renal capsule constitutes another major concern. Last but not least, using fluoroscopy during percutaneous access to the kidney is accompanied by the exposure of the operators, patients as well as the other working staff to radiation. Long-term ionizing radiation may lead to considerable hazardous effects on certain organs (15). Taking the above mentioned problems related to fluoroscopic access into account, endourolo- gists began to use sonographic guidance more common- ly then ever in an attempt to avoid such certain problems with some certain advantages. First of all, this approach is totally free of ionizing radiation with shorter operating duration (16). Additionally, this form of guidance allows the endourologist to identify the neighboring organs in an accurate manner to minimize the risk of injury (17). Lastly, the European Association of Urology recommends the initial puncture under sonographic guidance because it reduces radiation hazards (18). As stated above use of sonographic guidance in gaining access to the renal collecting system gained more impor- tance than ever in the last decade. Related with this issue, in a prospective and randomized study Zu W et al., aimed to compare the safety and efficacy of fluoroscopic (FG), total ultrasonographic (USG) and combined (CG) guidance for percutaneous renal access during mini-percutaneous nephrolithotomy (mini-PCNL) in a total of 450 consecutive patients with renal stones larger than 2 cm. While the overall complication rates using the Clavien grading sys- tem as well as stone free rates were similar between the three groups; multiple-tracts PNL were used more fre- quently in the FG and CG group than USG group and the mean access time was longer in CG than for FG and USG group patients. Mean total radiation exposure time how- ever was significantly greater for FG than for CG (19). In another study again, 45 children with unilateral stones underwent PNL procedures under totally sonographic guidance with a mean time to establish access as 2.9 (range 2.1-5) min. Blood loss requiring transfusion, sepsis, adjacent organ injury and kidney loss were not observed in any case and the authors concluded that the ultra- sound-guided mini-PCNL is feasible and safe in patients aged < 3 years, without major complications or radiation exposure (20). Last but not least, in their well organized systematic literature review including 18 studies with 2919 patients, Liu Q et al. stated in the final analysis that when compared with fluoroscopic guidance, use of ultra- sonography provided shorter puncture time, higher suc- cess rate of fist puncture, less blood loss, and less compli- cations as the main advantages of this approach (21). On the other hand again, sonographic access to the kidney will be more practical and safe in relatively dilated reno- ureteral units in experienced hands. Easy and quick iden- tification of the renal structures but most important the desired calyx in such dilated kidneys will allow the endourologist to establish the puncture in a safe manner which will diminish the importance of open end ureteral catheter insertion to a certain extent. Thus, taking the advantages of renal puncture in a safe and quick manner under sonographic guidance in dilated kidneys as well as the problems related to open end ureteral catheter place- ment into account use of an open end ureteral catheter in all cases becomes really questionable. Regarding the per- formance of percutaneous nephrolithotomy without open end ureteral catheter insertion, there is highly limited data reported so far in the literature. Only one study conduct- ed by Tabibi et al. compared the outcomes of renal calyceal system puncture with and without retrograde pyelography in 55 patients with opaque renal calculi. They were able to show no differences in outcome, infection, operative time, duration of hospital stay, and radiation exposure, indicat- ing that ureteral catheter placement may be precluded (22). We believe that our current study is a comprehensive one focusing on this critical issue in a detailed manner. In this present study we aimed to evaluate the true necessity of open end ureteral catheter insertion in terms of the success as well as safety of renal puncture in patients with diated pelvicalyceal system (Grade 2 or higher) performed under sonographic guidance by com- paring them with the cases in whom the catheter was inserted. Our results demonstrate clearly that the mean total duration of the PNL procedure in cases with open end ureteral catheter was significantly longer than the other cases. However, use of open end ureteral catheter did not shorten the renal access time in both groups of cases indicating that the presence of a dilated system doesn’t require a catheter placement particularly in the light of the disadvantages mentioned above. Evaluation of the outcomes of the PNL procedures in terms of success rates as well as early post-operative fol- low-up data revealed no statistically significant differ- ence between the two groups regarding the stone-free rates (84% vs 88%). Additionally, when we evaluated our cases in both groups with respect to nephrostomy tube duration, hospitalization period and percentage of secondary procedures, no statistically significant differ- ence again could be demonstrated from these aspects. Last but not least, as an important parameter again, although the mean fluoroscopic exposure time was rela- tively longer in cases treated with open end ureteral catheter, this difference was not statistically significant. Our results demonstrate clearly that despite its well- known advantages during PNL procedure performed under fluoroscopic guidance; placement of an open end ureteral catheter may not really be necessary particularly in selected cases with a dilated renal collecting system Eryildirim _Stesura Seveso 28/09/17 10:27 Pagina 230 231Archivio Italiano di Urologia e Andrologia 2017; 89, 3 Do we really need ureteral catheter in dilated systems during PNL? operated under sonographic guidance. Renal puncture under sonographic guidance can be done in a safe and practical manner in experienced hands in such cases with- out any need for such a catheter placement. Furthermore visualisation of the entire collecting system could be done via antegrade way in all these cases whenever needed. It should be kept in mind that; open end ureteral catheter insertion is a time consuming procedure which will in turn definitely prolong the total duration of a certain pro- cedure during which the patient receives anesthesia in an unusual position. Additionally, when we add the time period needed for the change of the position from lithoto- my to prone in the majority of the cases again the total duration of the intervention (as well as the anesthesia) will further increase in these cases. Additionally, it is very clear that urethra as well as ureter are both exposed to a certain degree of trauma during stent placement particularly in male cases. Taking all these facts into account, we believe that an open end ureteral catheter may not be inserted in selected cases treated with PNL under sonographic access for solitary renal pelvic and/or calyceal stones causing dilatation in the upper urinary tract. Our study may have one limitation: The number of cases included and evaluated may be small. But taking the lack of publications regarding this issue and comprehensive evaluation of the necessity for an open end ureteral catheter performing PNL in dilated renal systems under sonographic guidance, we believe that our current find- ings will certainly be contributive enough to the existing literature on this critical subject. CONCLUSIONS In the light of the findings obtained in our current study and the above mentioned well known associated prob- lems, we believe that placement of an open end ureteral catheter prior to a PNL procedure performed under sonographic access may not be indicated in selected cases presenting with solitary renal pelvic and/or calyceal stones causing dilatation in the upper urinary tract. REFERENCES 1. Fernstrom I, Johansson B. Percutaneous pyelolithotomy. A new extraction technique. Scand J Urol Nephrol. 1976; 10:257-9. 2. 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Correspondence Bilal Eryildirim, MD (Corresponding Author) bilaleryildirim@yahoo.com Murat Tuncer, MD - murattuncer77@hotmail.com Emre Camur, MD - emre.camur@outlook.com Fatih Ustun, MD - drfatihustun@gmail.com Fatih Tarhan, MD - tarhanf@yahoo.com Kemal Sarica, MD - saricakemal@gmail.com Dr. Lütfi Kirdar Training and Research Hospital Urology Clinic Istanbul, Turkey Eryildirim _Stesura Seveso 28/09/17 10:27 Pagina 231