Factors Affecting Retrograde Intrarenal Surgery Success: 6 Years Experience of a Clinic in Central Anatolia

Introduction

Urinary system stone disease is an important health problem. It has been reported to have a prevalence of 14.8% in Turkey. ¹ Shock wave lithotripsy (SWL), percutaneous nephrolithotomy (PNL), and retrograde intrarenal surgery (RIRS) are used in the treatment of urinary system stones. RIRS was first used in 1964 (Ref. ² ). At first, RIRS was used for the treatment of stones <20 mm in size, in which SWL has failed. However, advances in laser and flexible ureterorenoscope and increasing experience widened the usage of RIRS. Nowadays, RIRS is used for the treatment of stones >2 mm in size. ³

The aim of the renal stone removal surgery is to clear the stones with minimal complications. PNL has high success rates, but its complications can be mortal. ⁴ RIRS is a safe method due to the fewer and minor complications, however it may require several sessions that may result in extra cost and stress. ⁵

There are numerous studies that investigated various factors, including anatomical features affecting RIRS success.^3,6,7 As a clinic in central Anatolia, we aimed at researching the factors affecting RIRS success in our area.

Methods

After local ethics committee's approval, the data of the patients who had undergone RIRS due to kidney stones between 2014 and 2019 were reviewed. Patients who were <18 years old, had kidney anomalies, and had both ureter and kidney stones were excluded from the study.

Informed consent was obtained from all of patients before the operation. Demographic, preoperative, and postoperative data were recorded. Routine blood tests were performed preoperatively. Kidney, ureter, and bladder graphy (KUBG), ultrasonography (US), intravenous urography, and unenhanced computed tomography (CT) were performed preoperatively. For opaque stones, the stone size was measured as the longest diameter in KUBG. For non-opaque stones, stone size was measured by using US. Stone volume was measured by using CT.

Parenteral antibiotic was administered 1 hour before the operation. After induction of anesthesia, patients were placed into modified supine lithotomy position and 0.035/0.038 inch hydrophilic guidewire was placed into the pelvis after semi-rigid ureterorenoscopy. Ureteral access sheath (UAS) (9.5/11.5 F or 11/13 F) (Elite Flex, Ankara, Turkey) was placed over the guidewire. A flexible ureterorenoscope was advanced through the UAS, and access to the stone was achieved. Unless UAS was placed, a flexible ureterorenoscope was advanced over the guidewire. Fragmentation was performed with holmium:YAG (Ho YAG Laser; Dornier MedTech; Munich, Germany/Dornier Med-Tech GmbH, Medilas H20 and HSolvo, Wessling, Germany) laser by using dusting and fragmentation methods. Double-J (JJ) stent was inserted due to intraoperative conditions. A urethral catheter was inserted at the end of the operation. Time between endoscopy and JJ stent insertion was defined as operation time. The urethral catheter was removed on postoperative 1st day, and JJ stent was removed 3 weeks after the operation.

KUBG was performed for opaque stones, and US was performed for non-opaque stones on postoperative 1st day. CT was performed on postoperative 3rd month follow-up. After the follow-ups, patients who were stone free or had clinically insignificant residual stones (CIRF) (<3 mm) were considered as successful. The patients who had a successful outcome of the procedure were included in Group 1, whereas the rest were included in Group 2. The demographic, intraoperative, and postoperative data of the two groups were compared. Patients' stone localization (mid, lower, and multicaliceal stones, and upper calix, including upper pole, pelvis, and proximal ureter) and stone number (single or multiple stone) were also compared between the groups.

Demographic, preoperative, and postoperative data were recorded. The patients who were defined as successful were named as Group 1 and the others were named as Group 2. The demographic, intraoperative, and postoperative data of the two groups were compared.

Statistical analyses

The statistical evaluation of the data was performed by using IBM SPSS Statistics for Windows, v25.0 (IBM Corp. Released 2017. Armonk, NY). Continuous and categorical variables were defined as mean ± standard deviation and percent (%), respectively. Kolmogorov–Smirnov test was applied to the variables to estimate the distributions of the parameters. Mann–Whitney U test was utilized for variables of quantitative data that had non-normal distribution. The Chi-square and Fisher's exact tests were used for the comparison of quantitative data. Binary logistic regression test was the choice to find the predicting factors of RIRS success. The level of statistical significance was defined as P < .05.

Results

There were a total of 416 patients in our study. Group 1 consisted of 332 patients, whereas Group 2 had 84 patients. Age, gender, stone laterality, preoperative SWL history, history of previous operations, stone localization, and single stone rate were similar between the two groups. Opacity was significantly different between the groups (P = .004). Stone size, stone volume, and operation time were significantly higher in Group 2, whereas postoperative JJ stent rate was similar between two groups. The UAS usage was significantly higher in Group 2. A flexible ureterosope was advanced over the guidewire in 2 patients from Group 1, and in 1 patient from Group 2 (Table 1).

In our study, the total success was 79.8%. The results of the binary logistic regression analysis are given in Table 2. Omnibus tests, model summary, and Hosmer–Lemeshow test results were appropriate for the model of this study. We found that stone size, opacity, and operation time affected the success of RIRS significantly (P < .05). There was a reverse relationship with stone size, operation time, and opacity. The decrease in these parameters resulted in higher success rates after RIRS. When we look at the odds ratio values, there was a modest relationship between both stone size and operation time. However, there was a significant relationship in opacity [Exp(B) = 0.022]. Stone locations were also evaluated with the logistic regression analysis. Only upper versus lower pole comparison was significant, and treatment of upper pole stones had 2.5 times more success than lower pole stones [P = .013; Exp(B) = 2.55] (Table 2).

Discussion

The aim of stone surgery is to clear the stones in the most efficient and safe way. Therefore, the chosen method has to be efficient and the complications should be low. RIRS was first used in the treatment of stones <2 cm, but nowadays RIRS can be used to remove stones >2 cm. RIRS is a reliable and efficient method. ⁸ It is important to choose an appropriate treatment method for each patient. In this study, we aimed at reporting findings from our clinical experience that span 6 years.

In our study, success rate was 79.8%. Resorlu et al. reported 80.6% success rate after 3 months of follow-ups. ⁹ In another study, stone free rate was 57% (Ref. ⁶ ). The definition of success is also important. Resorlu et al. defined success as being stone free or having <4 mm CIRF. ⁹ The other study defined success as being stone free. ⁶ In our study, we defined success as being stone free and having <3 mm CIRF. Our results were compatible with the literature.

Stone size was 12.24 ± 5.03 mm in the successful group (Group 1), whereas in the unsuccessful group (Group 2), stone size was 15.94 ± 5.83 mm. Results were similar with the literature. Tonyalı et al. reported a stone size of 14.2 ± 5.3 mm in the successful group and 15.2 ± 6.1 mm in the unsuccessful group. ⁶ Ito et al. reported stone sizes of 16.92 ± 10.22 mm and 36.42 ± 18.51 mm in the successful and unsuccessful groups, respectively. ¹⁰ In a study researching the factors affecting success in the lower calix stones, the mean stone size was 10 mm. ³ In our study, stone size was significantly higher in the unsuccessful group, which was an expected result.

According to the results of our study, age, gender, and stone laterality did not affect RIRS success. Our results were similar with literature.^3,6,9 Several studies have reported that SWL and history of previous operations did not affect RIRS success, whereas others contradicted those results.^11–13 Moreover, preoperative JJ stent and UAS usage were reported to affect RIRS success.^6,14 In our study, we found that preoperative JJ stent history, SWL history, history of previous operations, and UAS usage did not have any effect on RIRS success. Different from the literature, we found that opacity was adversely affecting RIRS success. ⁶ This result can be explained by the fact that fragmentation is usually more effective in non-opaque stones due to its soft nature.

There is no consensus on whether the localization of the stone affects the RIRS success. Although there are studies reporting that stone localization affects RIRS success, there are also studies reporting otherwise.^6,13,15 In particular, the effect of lower calix localization on RIRS success has also been highly debated.^10,16 Multicaliceal localization has also been reported to affect RIRS success. ¹⁶ Martin et al. reported that lower calix localization affects RIRS success in case of multicaliceal stones and previous PNL history. ¹⁷ Stone localization did not have an effect on RIRS success in our study, which can be explained with the low rate of lower calix stones.

Another factor in the success of RIRS is the stone number.^18,19 Most of the studies in the literature report that stone size does not affect RIRS success. In our study, we defined the stones as single and multiple and single stones did not affect RIRS success.

The effect of stone size on RIRS outcome is another contentious topic. In our study, we found that stone size affected RIRS success. Resorlu et al.'s findings were in agreement with our results, whereas some other studies reported otherwise.^3,6,18

In our study, stone volume did not affect RIRS success, which was similar to some other studies. ⁶ Ito et al. stated that Hounsfield unit (HU) does not have an effect on RIRS success. ¹⁹ We did not evaluate the HU in our study.

We found that operation time was significantly longer in the unsuccessful group. This result was not surprising, due to the larger stone sizes in that group. Different from the literature, we found that prolonged operation time had a negative effect on RIRS.

Anatomical factors affecting RIRS success were investigated, especially in lower calix stones.^7,20 Kılıcarslan et al. found that infundibular width (IW) and infundibulopelvic angle were affecting RIRS success after univariate analysis, whereas IW was affecting RIRS success after multivariate analysis. ³ In our study, we examined only calix stones, so we did not evaluate anatomical factors.

Retrospective design and absence of stone analysis are disadvantages of our study. We aimed at presenting our findings from 6 years of RIRS experience in Central Anatolia. There are a few studies reporting that stone composition has an effect on RIRS success. ¹⁸

When we look at the advantages of our study, different from the literature we showed that operation time and opacity were adversely affecting RIRS success. The significance of our study is in its population size. In two studies that investigated RIRS success, the number or observed patients were 207 and 382, whereas in our study that number was 416 (Refs.^18,21).

Conclusion

In conclusion, RIRS is a safe and efficient method in patients with favorable conditions. Stone size, opacity, and operation time are factors that could affect the outcome of RIRS. We believe that in patients who have large lower calix stones and who want effective treatment, PNL should still be an option for treatment.