Navigating Entire Collecting System During Supine Percutaneous Nephrolithotomy: Is Rigid Nephroscopy Enough? A Prospective Study by International Alliance of Urolithiasis Supine Percutaneous Nephrolithotomy Working Group

Introduction

International guidelines such as the European Association of Urology (EAU) and the International Alliance of Urolithiasis (IAU) emphasize that percutaneous nephrolithotomy (PCNL) is the main treatment option for the surgical management of kidney stones >20 mm in diameter.^1,2 The main treatment goal during any endourology procedure is complete stone clearance alongside minimal morbidity. Despite the advancements in the operative technique and endoscopic equipment technology, the stone-free rates after PCNL have been reported to be less than 60% for staghorn stones. ³

In such complex cases, accessibility to the entire collecting system is crucial to check the presence of any residual stone fragments. In a previous study, Sofer et al. reported successful access to the upper pole through a lower pole puncture in 80% of the cases operated in the supine position. ⁴ The same group published another study to evaluate the role of morphometric and clinical factors on this aspect and reported 82% success rate in approaching the upper pole through a lower-pole puncture in the supine position. ⁵ These outcomes are promising and therefore suggest the lower pole as an ideal site for puncture during supine PCNL.

However, access to the entire collecting system is not always possible with this approach. In a previous study, by performing retrograde flexible ureterorenoscopy, the authors were able to detect the residual stone fragment(s) in 13.1% of the cases at the end of the procedure. ⁶ In addition, puncture through the middle- or upper-pole calyces may be necessary depending on the stone burden and patients' habitus in some cases.

In the currently available literature, there are no studies evaluating the possibility of navigating the entire collecting system with a rigid nephroscope during supine PCNL. In this study, we aimed to identify the rate of accessibility of all caliceal cavities using lower-, middle- and, upper-pole punctures and the eventual benefit of simultaneous utilization of retrograde/antegrade flexible nephroscopy.

Materials and Methods

In our current study, data derived from adult patients undergone PCNL in the supine position for renal stones in five different institutions affiliated with the IAU, supine PCNL Working Group, were collected prospectively. The study protocol was approved by the Institutional Review Board (Approval number: 2021/40-3). Data were collected through an online collection platform (https://www.jotform.com/) between May 2021 and January 2023.

In addition to the size of the stone treated, certain patients (age, gender, body mass index, American Society of Anesthesiologists status, presence of renal anomalies, previous operations) and procedure/operative technique (percutaneous tract size, nephroscope size, type of flexible endoscope, stone size, percutaneous access site) (lower, middle, or upper pole), operational time, access status to the other poles of the kidney with rigid nephroscope, antegrade access status to the other poles of the kidney with flexible nephroscope, or retrograde access with flexible ureterorenoscope were all evaluated and recorded in all cases.

In addition, the detection of residual fragments in other poles with endoscopy, postoperative imaging modality, detection of residual fragments in postoperative imaging, perioperative complications, hemoglobin drop, need for auxiliary procedures, and need for hospitalization within 3 months after surgery were also assessed and recorded. Patients were defined stone free in case of the absence of residual fragments of any size. Successful access of the other poles by both for rigid and flexible endoscopes was defined as the observation of two caliceal papillae in the targeted calyx.

Statistical analysis was performed with SPSS ver. 20.0 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.). Patient characteristics were summarized using mean ± standard deviation for continuous variables and frequency (percentage) for categorical variables. The chi-square test or Fisher's exact test was used to compare the categorical variables. For statistical significance, P value of .05 was accepted.

Results

Data obtained from a total of 226 patients were analyzed. The mean age of the population was 51.6 ± 8.8 years and while 93 (41.1%) of the patients were females, 133 (58.9%) of the patients were males. The mean stone size was 38.4 ± 8.2 mm. Retrograde flexible ureterorenoscopy was carried out in 166 (73.5%) of the patients, while an anterograde flexible nephroscopy was performed in 60 (26.5%) of the patients. Stone-free status was achieved in 207 (91.6%) of the patients. Median length of hospital stay was two (1–7) days. The demographic, stone-related, and operative characteristics of the patients were summarized in Tables 1 and 2.

Lower-pole puncture was performed in 97 (42.9%) cases. With the rigid nephroscope, a successful approach to the middle pole and upper pole was possible in 36 (37.1%) and 66 (68%) of the cases, respectively. During flexible nephroscopy, while the upper pole was successfully approached in all of the 97 patients, the middle pole was successfully approached in 94 (96.9%) of the patients. In all 3 patients with a failed approach, anterograde use of a flexible nephroscope was performed. Residual stones were detected in the middle- or upper-pole calyces in 9 (9.3%) patients with rigid nephroscope and in 12 (12.4%) additional patients with flexible nephroscope.

Middle-pole puncture was performed in 72 (31.9%) of the patients. With the rigid nephroscope, a successful approach to the upper pole and the lower pole was possible in 40 (55.5%) and 38 (52.7%), respectively. With flexible nephroscopy in these cases, while upper pole was successfully approached in all of the 72 patients, the lower pole was successfully approached in 63 (87.5%) of the patients. Although antegrade use of flexible nephroscope was performed in 6 of these 9 patients with a failed approach, retrograde flexible ureterorenoscopy was performed in the remaining 3 patients. Residual stones were detected in lower- or upper-pole calyces in 6 (8.3%) patients with rigid nephroscope and in 10 (13.8%) additional patients with flexible nephroscopy.

Upper-pole puncture was performed in 57 (25.2%) of the patients. With the rigid nephroscope, a successful approach to the middle pole and the lower pole was possible in 20 (35.1%) and 18 (31.5%), respectively. With flexible nephroscopy, the middle pole was successfully approached in 54 (94.7%), while the lower pole was successfully approached in 55 (96.5%) of the patients. In all of the patients with failed approach, antegrade use of flexible nephroscope was performed in all cases but one with failed access to the lower pole with retrograde flexible ureterorenoscopy due to an acute angle. Residual stones were detected in middle- or lower-pole calyces in 3 (5.3%) patients with rigid nephroscope and in 5 (8.8%) additional patients with flexible nephroscopy.

The entire collecting system could be successfully approached by a rigid nephroscope in 50% of the cases through middle-pole puncture. This rate was significantly higher than the 37.1% successful approach rate through lower-pole puncture and 28.1% successful approach rate through upper-pole puncture (P = .035). When the success rates of anterograde and retrograde flexible nephroscopy are compared, with retrograde approach successful approach to the entire collecting system was possible in 162 of the 166 cases (97.6%), while the successful approach was possible in 48 of the 60 cases (80%) with the anterograde approach (P < .0001).

Postoperative imaging was performed with a noncontrast computed tomography (CT) scan in 138 (61.1%) of the patients. Ultrasonography and a kidney, ureter, and bladder (KUB) X-ray were the imaging modalities in 28 (12.4%) and 20 (8.8%) patients, respectively. In 40 (17.7%) patients, however, both ultrasonography and KUB were performed. The mean hemoglobin drop was 1.1 ± 0.8 g/dL and blood transfusions were needed in 2 (0.8%) patients. No complications were observed in 168 (74.3%) patients. Clavien grade I, grade II, and grade III complications were observed in 33 (14.6%), 23 (10.2%), and 2 (0.8%) patients, respectively. While 1 patient with grade III complications had a pseudoaneurysm requiring angioembolization, another patient required a chest tube due to hydrothorax.

Discussion

The main goal of an endourology procedure for urolithiasis is to establish a stone-free status and postprocedural endoscopic navigation of the entire collecting system seems to be the most reliable way of evaluating the presence of residual fragments. In this study, we aimed to outline the successful navigation of the entire collecting system with both rigid and flexible endoscopes based on the renal calyx punctured. We found out that the use of flexible endoscopes may significantly improve the accessibility of the entire collecting system.

Reaching the entire collecting system is crucial for an optimum outcome during PCNL. For this purpose, upper pole punctures are reported to be more suitable in a prone position as it gives direct access to the renal pelvis and lower pole in most cases and limit number of punctures needed.^7,8 However, as the upper pole punctures are associated with higher risk of pleural iatrogenic injuries, performing a subcostal puncture through the lower pole will be more rational if it gives access to all of the stone burden. ⁹ Related to this issue, Sofer et al. demonstrated that upper-pole calyces can be well accessed through a lower-pole puncture in 80% of the cases in a supine position compared to a 20% rate obtained in the prone position. ⁴

In another study, they further evaluated the possible role of morphometric and clinical factors on access rates to the upper pole access through a puncture made at the lower pole. The authors demonstrated an 82% access rate to the upper pole and the angle between the lower and upper pole was the only prognostic factor for successful access to the upper pole. ⁵

In our current study, we were able to reach the upper pole through a lower-pole puncture in 68% of the cases and this rate was slightly lower than the rates reported by Sofer et al.^4,5 We believe that the difference is mainly related to the definition of successful access in previous trials, which was defined as the visualization of a single papilla in the upper-pole calyces. In our trial, we defined the same criteria by visualization of at least two papillae. More importantly, we also investigated the access to the middle pole through the lower pole puncture and we were able to reach the middle pole in only 37% of the cases. This finding has a certain clinical significance especially in cases with complete staghorn stones. Removal of all stone burden with a single lower pole access would only be possible in 1/3 of the cases in whom the stone fills all lower-, middle-, and upper-pole calyces.

Upper-pole punctures have been proposed to be more difficult in the supine position due to the limited area for puncture and also the longer distance from the skin to the desired caliceal system. In our study, we determined that following an upper pole puncture, an approach to the middle and lower pole was possible only in 20 (35.1%) and 18 (31.5%) patients, respectively, by using the rigid nephroscope. Therefore, in patients with an upper-pole stone, a flexible endoscope should be available to check the collecting system for residual fragments due to the high possibility of stone migration to other parts of the collecting system.

Endoscopic Combined Intrarenal Surgery (ECIRS) was introduced by Scoffone et al. in 2008. ¹⁰ Since then, simultaneous use of retrograde flexible ureterorenoscopy has become more popular and has additional benefits. ¹¹ One of the most prominent advantages of ECIRS is the evaluation of the collecting system at the end of surgery for the precise detection of residual fragments. Fluoroscopy-based evaluation of residual fragments is not reliable and, in one study, the authors reported a negative predictive value of 72% for the presence of residual fragments concerning surgeon's evaluation via fluoroscopy. ¹² In another study, Portis et al. reported a negative predictive value of 73% for the detection of residual fragments despite the use of a flexible nephroscope. ¹³

In a more recent study, anterograde and retrograde nephroscopy were compared for successful evaluation of the collecting system and detection of residual fragments in a cohort of patients undergoing ECIRS for complex renal stones. ⁶ In this study, while successful navigation of the entire collecting system was possible in 94.9% of the patients with retrograde flexible ureterorenoscopy, this rate was 73.7% for the anterograde approach. In the same study, antegrade flexible nephroscopy revealed the presence of residual fragments in 13.1% of the patients despite the surgeon's decision on stone-free status with fluoroscopy and rigid nephroscopy. In 17 additional cases, however, the retrograde approach revealed residual stones as well. ⁶ In some of the collecting systems, there might be parallel calyces in the punctured pole of the kidney. With a rigid nephroscope or with anterograde flexible nephroscopy, these parallel calyces could not be approached, and this may lead to incomplete stone clearance.

Although this study showed a clear benefit of retrograde flexible ureterorenoscopy, the authors did not evaluate the possible effect of the punctured calyx on the outcomes of the procedure. In our study, we reported the chance of successful access to the other parts of the collecting system based on the punctured calyx. Successful access to the upper pole with the flexible nephroscope was possible in all of the cases punctured through lower- or middle-pole calyces. On the contrary, successful access to the middle-pole calyces was not possible in 3.9% of the cases in whom the puncture was made through lower- or upper-pole calyces. Successful access to the lower pole was not possible 8.5% of the cases where the puncture was made through upper- or middle-pole calyces.

At the end of the surgery, with the additional role of flexible nephroscopy, we detected residual fragments in 13.2% of the patients. This rate is compatible with the reported residual fragment detection rate of 13.1% from the above-mentioned study. ⁶ Residual fragments following PCNL can lead to regrowth, symptomatic obstruction, and urinary tract infections.^14,15 Following PCNL, stone-related events were reported in 46.1% of the cases with residual fragments. ¹⁶ Therefore, reliable and precise detection of residual fragments at the end of surgery with flexible nephroscopy evaluation, not only improves the stone-free rates but also decreases the necessity of a postoperative CT scan evaluation and also diminishes the rates of stone-related events.

However, it is obvious that the use of a flexible nephroscope and flexible ureterorenoscope during PCNL results in extra costs for the procedure. In addition, flexible endoscopes may not always be readily available in the operating room especially in developing countries. Also, health insurance systems usually do not pay for the additional flexible nephroscopy in most countries. Therefore, despite the above-mentioned benefits of this procedure, we cannot advocate the routine application of flexible nephroscopy during PCNL in every case and the surgeons should decide well about the site of puncture particularly based on the stone burden and patient anatomy.

The most important drawback of our study is that not all of the patients underwent a postoperative noncontrast CT scan. Therefore, it is possible that some of the patients, especially the ones with some of the calyces could not be reached with flexible endoscopy, may still have some residual fragments despite the use of flexible nephroscopy. Also, there is no standardization of the tract size, type of rigid and flexible endoscopes, patient positioning, and also the surgeons' experience. We also did not have a control group of patients who did not undergo a flexible nephroscopy, and so, we do not have the chance to evaluate the additional role of the flexible nephroscopy for stone-related events in the long term. However, we still believe that our study is valuable as it is unique for evaluating the role of rigid and flexible nephroscopy in this aspect particularly based on the punctured calyx.

Conclusion

Evaluation of the entire collecting system with rigid nephroscopy is not possible in a significant portion of the patients during PCNL. Additional use of flexible nephroscopy significantly improves the successful navigation of the entire collecting system, which will ease the detection of residual fragments. Therefore, we believe that the application of flexible nephroscopy, particularly via retrograde approach could be beneficial to improve the stone-free rates and diminish the rate of future stone-related events if the necessary expertise and scope are available.

Ethical Approval

The study was approved by our Institutional Ethics Committee (Ankara University School of Medicine, Ankara, Turkey). The local Ethics Committee's registration number is 2021/40–3.