Comparison of the Efficacy and Morbidity of Flexible Ureterorenoscopy for Lower Pole Stones Compared with Other Renal Locations

Introduction

Management of lower pole stones (LPS) can represent a therapeutic challenge. Before the development of flexible ureterorenoscopy (f-URS), extracorporeal shockwave lithotripsy (SWL) was the gold standard treatment for patients with small or moderate size LPS in view of its efficacy, low complication rate, and good tolerance. For larger stones, percutaneous nephrolithotomy (PCNL) is the recommended treatment.

The stone-free rate (SFR) after SWL treatment for LPS, however, varies from 25% to 85%. ¹ These results are lower than those for other renal locations. The anatomy of the lower pole calix, especially the infundibulopelvic angle, as well as gravity have been proposed as possible factors responsible for poor clearance of fragments after SWL. ^{2 –4} PCNL has proven to be highly successful for the management of LPS, regardless of stone size. It is associated with higher morbidity ^5,6 than SWL and f-URS, however, although results are reportedly comparable between PCNL and f-URS for the management of LPS. ⁵

With the development of endoscopic techniques and the miniaturization of equipment, f-URS coupled with endocorporeal lithotripsy by holmium-yttrium-aluminum-garnet laser seems to represent a minimally invasive and effective therapeutic approach for LPS, achieving a higher SFR than SWL, with a comparable complication rate. ^7,8 Indeed, Pearle and associates ⁹ reported a significantly higher SFR after f-URS compared with SWL for LPS for lower pole caliceal calculi measuring 1 cm or less.

Despite technologic and technical progress, however, the drawback of f-URS is that deflection of the flexible ureterorenoscope is limited when the working channel is used. This makes access to the lower pole difficult, leading to the use of specific techniques to access the lower pole calix. ¹⁰

The objective of this study was to evaluate the impact of stone location on the efficacy and morbidity of f-URS by comparing procedures performed for LPS with those performed for other renal locations.

Patients and Methods

We performed a retrospective study between January 2004 and December 2010. All f-URS performed for upper urinary tract stone retrieval in our institution were eligible for the analysis, corresponding to a total of 497 procedures in 373 patients. Of these, 126 procedures performed for ureteral stone location were excluded, and the remaining 371 procedures were included in this analysis. Each procedure was considered on an individual basis. Among the 371 procedures included in this analysis, 139 were performed for stones located in a renal location other than the lower pole (group 1), and 232 procedures were for stones located in the lower pole (group 2). Multiple stone locations including at least one lower pole location were included in group 2, whereas patients with multiple stone locations without any lower pole location were included in group 1.

Recorded data included demographic data for each patient (age, body mass index [BMI], preoperative stent placement), stone characteristics (stone composition, location, diameter of the largest stone), procedural characteristics (procedure duration, relocation, use of ureteral access sheath, placement of ureteral stent), mean length of stay and procedural outcomes (i.e., the SFR at 6 months), surgical complications according to the Clavien-Dindo classification ¹¹ (hematuria, flank pain, and sepsis).

Follow-up was standardized and included simple radiography coupled with ultrasonography or renal CT scan. The primary end point was success of f-URS (SFR) defined according to a very stringent definition of the SFR—namely, complete stone-free status at the last follow-up visit at 6 months. Presence of residual fragments was considered a failure, regardless of the size of the residual fragment(s). All f-URS were performed by experienced operators (EC, GG, SB, HB, FK) following a standardized protocol previously described by Delorme and colleagues. ¹² Endoureteral Double-J stents or ureteral stents could be used in this study, at the surgeon's discretion.

Results

Patient and stone characteristics are presented in Table 1. Age, sex, mean BMI at the time of surgery, and preoperative stent placement rate did not differ between groups. History of urolithiasis was comparable between group 1 and group 2 (P=0.14). No differences in stone characteristics were observed between the two groups in terms of stone size or composition. However, The percentage of stones <10 mm, however, was significantly higher in group 2 compared with group 1 (P=0.018).

The procedural characteristics are described in Table 1. The mean duration of the procedure was comparable between groups 1 and 2 (P=0.76). Access sheaths were widely used to allow optimal irrigation flow and were significantly more frequently used in group 2 (P=0.007). Monobloc extraction was performed in 18.2% in group 1 vs 18.7% in group 2 (P=0.91) for a mean stone size of 6.02 mm. For LPS, relocation was performed in 19.8%, depending on accessibility and surgeon's experience.

Outcomes of f-URS are described in Table 2. The SFR was comparable between groups 1 and 2 (P=0.77). The complication rate was similar between groups, as was the severity of complications. No complications requiring surgical intervention (Clavien-Dindo grade III) were observed. No complications of anesthesia occurred during endoscopic procedures or in the 2 days after surgery in either group. No lesion resulting from the use of an access sheath and no ureteral strictures were observed.

The SFR for stones <10 mm and complication rates are described in Table 2. The SFR was comparable between groups 1 and 2 (P=0.45). Complications were comparable between the two groups.

The results of multivariable analysis by logistic regression identifying the predictors of treatment failure are described in Table 3. Stone size >10 mm (P<0.0001) and multiple stone locations (P=0.001) were significantly associated with treatment failure, as defined by a poor SFR. In our study, lower pole location was not independently associated with f-URS failure.

Discussion

Our study provides evidence that f-URS can yield similar results for the management of kidney stones regardless of their localization in the renal cavities, without influencing morbidity. Indeed, f-URS associated with intracorporeal lithotripsy is a minimally invasive technique for the manaagement of intrarenal stones. Current European Association of Urology guidelines ¹ recommend endourologic procedures as first-line treatment for patients with LPS >15 mm, in view of the poor efficacy of SWL in these cases, estimated to range between 25% and 85%. ¹ For stones >20 mm, PCNL remains the first line treatment. F-URS can be an option but depends on the operator's skill. For stones <10 mm, SWL or f-URS can be used. The endoscopic alternatives, however, can be considered in the presence of negative anatomic features rendering SWL less effective (e.g., steep infundibular-pelvic angle, long calix, or narrow infundibulum) or shockwave resistant stones. ¹ Several recent studies reported promising SFR of between 50% and 90% with f-URS for LPS. ^5,7,8,13,14

Sampaio and Aragao ¹⁵ first attributed the poor clearance of fragments after SWL for LPS to the anatomy of the lower pole calix. In 2012, Resorlu and colleagues ¹⁶ retrospectively analyzed 67 procedures for LPS and reported that the infundibulopelvic angle was the only statistically significant anatomic parameter to influence stone clearance after f-URS. Similarly, in 2013, Jessen and associates ¹⁷ evaluated the influence of the collecting system anatomy on the efficacy and morbidity of f-URS. They retrospectively evaluated 111 f-URS for LPS with modern flexible ureterorenoscopes. They concluded that stone size, long infundibulum, and infundibulopelvic angle <30 degrees negatively affected the SFR, with no influence on morbidity. Their findings support the idea that with the use of second-look procedures, a complete SFR can be achieved even when the anatomy is unfavorable.

In 2008, Perlmutter and coworkers ¹⁸ retrospectively evaluated the impact of stone location on 86 renal stones managed by f-URS and laser lithotripsy. They found that stone location does not significantly affect the SFR. Our results are in line with these findings. A more recent study by Martin and associates ¹³ retrospectively analyzed 89 f-URS for LPS compared with 73 procedures for non-LPS. After one f-URS, the SFR for LPS was 67.9%. By multivariate analysis, presence of multiple stones was the only statistically significant predictive factor of SFR. The authors concluded that f-URS for LPS appears to be an effective technique, although caution should be exercised for patients with multiple stones or a history of PCNL. F-URS morbidity was not evaluated in this study, however.

In addition, in 2012, Resorlu and colleagues ¹⁹ published a study evaluating the prognostic factors of f-URS effectiveness with the aim of proposing a predictive score for the SFR. They retrospectively analyzed 207 patients who underwent f-URS for renal stones. By univariate analysis, they demonstrated that size, number, composition of stones as well as the infundibulopelvic angle and renal malformations influenced the results of f-URS. By multivariate analysis, stone location did not seem to influence the SFR, whereas others factors maintained their statistically significant effect on success rate. In particular, lower pole location did not have a statistically significant influence on the SFR. Our study with a larger cohort confirmed these results, with no impact of stone location. It would have been interesting in our study to evaluate pyelocaliceal anatomy to assess its impact on the SFR, but unfortunately, the different imaging techniques used during the long period of recruitment did not permit such analysis.

In our study, complications according to the Clavien-Dindo classification were not statistically different between both groups. Indeed, there does not exist any significant differences either in the complication rate, or complication severity. All the complications observed were amenable to medical treatment. No complications classified as Clavien-Dindo III were reported. Based on these findings, it seems that stone location does not have any impact on the morbidity associated with this technique.

The technical artifice of the displacement of the stone into a more easily accessible location (upper pole or pelvic location) could explain why stone location did not have an impact on the SFR. Kourambas and coworkers ²⁰ showed that the SFR for LPS was significantly higher if stones were relocated (90% vs 83%). Moreover, Schuster and colleagues ¹⁴ showed that the SFR was significantly greater if stones were relocated, but only for stones of more than 1 cm (100% vs 29%, P=0.005). In our study, 46 LPS were relocated during the procedure and were treated in the renal pelvis or upper pole. The criteria for stone relocation were the size and accessibility of the stone, and the surgeon's experience. Because all analysis was performed on an intention-to-treat basis, these procedures were included in group 2 (lower pole stones) for methodologic reasons.

The development and the improvement of instruments such as nitinol baskets and small diameter laser fibers, thanks to their small size and good flexibility, limits the deflection loss of the flexible ureterorenoscope. Thus, these devices make it possible to reposition LPS toward locations where fragmentation is easier, or for treatment in situ. ²⁰ Local protocol in our center favors the wide use of access sheaths, especially in case of LPS, because access sheaths have been shown to protect the kidney and the ureter during the procedure, and to increase SFR. ²¹ A recent published report confirmed in a large retrospective cohort the safety of the ureteral access sheath, but failed to show any improvement in SFR among patients with vs without access sheath use. ²² Conversely, ureteral access sheaths have recently been shown to induce ureteral injuries, ²³ especially in patients without previous stent placement. Our study was not designed to analyze ureteral lesions caused by the access sheath, however, although we did observe that ureteral dilation was frequently needed to achieve ureteral access sheath placement in patients without stent placement. ²⁴ No ureteral strictures were observed in our study.

In 2008, Pearle and colleagues ⁷ published a multicenter prospective randomized study in which they reported a SFR of 50% for LPS under 10 mm. Several studies have reported SFR for LPS between 50% and 90%. ^5,7,8,13,14 The SFR for LPS in our study is lower than in some previously published works, at 68%. This could be explained by the very stringent definition of SFR we chose—namely, completely stone-free status. Our choice of this rigorous definition was justified by the importance of not underestimating, or overlooking tiny residual fragments, which although initially asymptomatic, could subsequently be the source of significant morbidity. ²⁵ The high rate of stones >10 mm in each group of our cohort could also explain this difference in SFR. In the subgroup analysis of stones <10 mm, the SFR observed in each group was similar to those observed in previously published works. ^5,8,13,14

Lastly, as Pearle and coworkers ⁹ underlined, the use of CT scan during follow-up for the evaluation of SFR can also explain the divergent results. Indeed, the greater sensitivity of CT scan, even for tiny residual fragments, contributes to a higher SFR during follow-up. ⁹ This was a possible bias of our study, with the nonuniform method of imaging during the long study period. At the start of our experience with f-URS, most patients were followed up by radiography and ultrasonography. This progressively changed over time, however, toward greater use of CT scanning for follow-up. Because all patients did not undergo CT scan in this study, this unfortunately precludes any evaluation of the predictive value of stone density on outcome as measured by CT scan. One could also criticize the number of surgeons involved in this study, which could introduce a bias in the results. To our mind, this is more likely to reinforce the results of this “real life” cohort of patient treated in a university tertiary center.

Conclusions

The results of our study demonstrate that f-URS achieves a high SFR for the management of kidney stones, regardless of their localization in the renal cavities, and with an acceptable level of morbidity. We showed that there was no difference in terms of efficacy and morbidity between LPS and other stone localizations.