Effect of Prestenting on Success and Complication Rates of Ureterorenoscopy in Pediatric Population

Abstract

Introduction:

In this study, we aimed to investigate the effect of prestenting on success and complication rates of pediatric ureterorenoscopy (URS) procedures.

Patients and Methods:

We retrospectively analyzed the data of 251 pediatric URS cases. Forty-seven of the patients were prestented. Success and complication rates of the prestented and nonprestented groups were compared and further analysis was performed with respect to stone location (renal vs ureteral) and size (7-mm cutoff). Multivariate analysis was performed to define factors associated with success rates.

Results:

Mean age of the population was 8.9 years. Success rate of the entire population was 80.5% and significant difference between prestented and nonprestented groups was detected (91.5% vs 77.9%, p = 0.04). Higher success rates of the prestented group were also observed in ureteral stones (94.1% vs 79.5%, p = 0.04) and stones >7 mm (84.6% vs 74.1%, p = 0.72). Prestented group showed higher success rates in kidney stones, but the difference was insignificant (84.6% vs 74.1%, p = 0.72). Prestenting was also identified as an independent predictor of success in multivariate analysis. Complication rate in the prestented group was also lower, but the difference was not significant (8.5% vs 14.7%, p = 0.347).

Conclusions:

Prestenting was found to increase the success rate of URS in cases of larger stones and ureteral stones in pediatric population. Prestenting also provides lower, but insignificant, complication rates. However, this procedure also has significant disadvantages. Based on the results of current study, we cannot recommend routine prestenting in pediatric cases. Instead, we recommend an attempt to treat the stone in the first session and place a stent in case of failed procedure to utilize potential benefits of prestenting while avoiding disadvantages.

Introduction

Worldwide increase in the incidence of stone disease is also observed in the pediatric population.¹ In case of active treatment indication together with extracorporeal shockwave lithotripsy (SWL), ureterorenoscopy (URS) is the preferred treatment option for treatment of renal and ureteral stones in the pediatric population.² In the presence of factors associated with decreased success rates of SWL such as the presence of calcium oxalate monohydrate or cysteine stones or stones in a system with anatomic abnormalities, URS becomes the preferred treatment option.^3,4

Technical improvements to provide better ureterorenoscopes with smaller size as well as flexible ureterorenoscopes with excellent deflection capacities maintained higher success rates for URS procedures.⁵ However, clinical research besides technological improvements still continues to improve the success rates while minimizing the complications. One of the factors that have been shown to facilitate the URS procedure is prestenting of the ureter before the procedure. Prestenting was shown to be associated with increased success rates or shorter operative time in a number of studies.^{6

–15} Based on these studies, the most recent EAU guidelines stated that prestenting facilitates the outcomes of URS; however, routine stenting is unnecessary.¹⁶

Most of the studies on prestenting before URS were performed in an adult population and there is only one study with limited number of patients reporting efficient and safe ureteral access after ureteral stenting in the pediatric population. However, this study did not report the detailed information on stone clearance rates and effect of prestenting on this parameter.⁷ Therefore, the current literature lacks information on the outcomes of URS after prestenting in comparison with a nonprestented group in the pediatric stone disease patients.

We believe that efficacy of prestenting in pediatric patients before URS should be evaluated distinctly from the adult population for two particular reasons: first, ureteral lumen is much narrower in pediatric cases, which certainly has an effect on efficient insertion of either the ureterorenoscope or the access sheath. Therefore, passive dilation with a ureteral stent may have greater potential to improve success rates and decrease complication rates. Second, the prestenting procedure usually requires general anesthesia in pediatric cases, which can usually be done under local anesthesia or mild sedation in adults. This factor also deals with potential advantages of prestenting during clinical decision-making. In this study, we aimed to investigate the effect of prestenting on success and complication rates of pediatric URS procedures in a tertiary academic center.

Patients and Methods

Data of 266 consecutive pediatric patients treated with semirigid or flexible URS for ureteral or renal stone disease in our center between January 2008 and October 2015 were investigated retrospectively. From this cohort, we evaluated the results of 251 patients who have records for the required data. Totally, 15 patients were excluded due to lack of follow-up information. Prestenting was defined as placement of a ureteral Double-J stent at least 1 week before the procedure.

Demographic, stone-related, and operative characteristics collected were age, gender, stone size, prestenting, localization and multiplicity, duration of operation, use of ureteral access sheath, placement of postprocedure stent, intraoperative complications, and success rates. Success rate was defined as no residual stones greater than 2 mm in diameter by the end of the procedure. We did not evaluate the complete stone-free rates as stone extraction is not routinely applied and limited to sampling for stone analysis in most of the cases. Complications were classified according to the modified Clavien system.¹⁷

Surgical technique

All procedures were performed under general anesthesia after antibiotic prophylaxis. A semirigid ureteroscope of 4.5F to 6.5F or flexible ureterorenoscope (Flex X2; Karl Storz, GmbH & Co., Tutlingen, Germany) was used. All patients underwent initial cystoscopy with a pediatric cystoscope to extract the ureteral stent and/or place a working guidewire. Ureteral orifice access was obtained atraumatically alongside or over a 0.035F guidewire. A manual irrigation pump system was used to hydrodilate the ureter during ureteroscopy. Access sheath (9.5F–11.5F, 13–20 cm Flexor Ureteral access sheath; Cook Medical, Inc., Bloomington, IN) was placed for the patients who had flexible URS over the safety guidewire whenever possible. Double-J stent was inserted as needed at the end of the procedure, according to the surgeons' preferences.

Patients were grouped as prestented or nonprestented and primary endpoint of the study was to determine the effect of prestenting on the success and complication rates. As a secondary analysis, we evaluated the effect of prestenting in subpopulations of ureteral and renal stone cases and stone ≤7 mm vs >7 mm groups separately.

Statistical analysis

Statistical analysis was performed with IBM SPSS Statistics for Windows, Version 20.0. (IBM Corp., Armonk, NY). Descriptive statistics for the parameters were provided. The prestented and nonprestented groups were compared with unpaired t-test or Mann–Whitney U test for the continuous variables and chi-square test or Fisher's exact test for the categorical variables. Logistic regression analysis was performed to define factors associated with success rates and factors that are found to be associated with success rates in the univariate analysis and were involved in a multivariate model. For statistical significance, p-value of 0.05 was accepted.

Results

Totally, data of 251 patients were evaluated. The mean age of the population was 8.9 ± 3.8 years and 150 (59.8%) of the patients were males, while 101 (40.2%) of them were females. Prestenting was performed in 47 (18.7%) of the patients and semirigid and flexible URS was performed in 180 (71.7%) and 71 (28.3%) patients, respectively. Mean stone size was 9.2 ± 3.8 mm and multiple stones were present in 65 (25.9%) of the patients. Postoperative ureteral stenting was performed in 219 (87.3%) patients and efficient procedure was established in 202 (80.5%) patients. Characteristic of the population with regard to prestenting is summarized in Table 1. Duration of operation was the only parameter difference between the prestented and nonprestented groups (54.6 vs 61.8 minutes, p = 0.02).

Table 1.

Demographic, Stone-Related, and Operative Characteristics of the Prestented and Nonprestented Groups

Parameter	Whole population (n = 251)	Prestented group (n = 47)	Nonprestented group (n = 204)	p-Value
Age, (years) mean ± SD	8.9 ± 3.8	8.3 ± 3.5	8.9 ± 3.9	0.26
Sex				0.51
Male, n (%)	150 (59.8)	26 (55.3)	124 (60.8)
Female, n (%)	101 (40.2)	21 (44.7)	80 (39.2)
Stone location, n (%)				0.97
Upper calyx	7 (2.8)	2 (4.3)	5 (2.5)
Middle calyx	9 (3.6)	2 (4.3)	7 (3.4)
Lower calyx	22 (8.8)	3 (6.4)	19 (9.3)
Renal pelvis	33 (13.1)	6 (12.8)	27 (13.2)
Upper ureter	58 (23.1)	12 (25.5)	46 (22.5)
Middle ureter	50 (19.9)	8 (17.0)	42 (20.6)
Lower ureter	72 (28.7)	14 (29.8)	58 (28.4)
Mean stone size, mm	9.2 ± 3.8	10.1 ± 3.9	9.1 ± 3.8	0.13
Presence of multiple stones, n (%)	65 (25.9)	14 (29.8)	51 (25.0)	0.58
Use of ureteral access sheath, n (%)	71 (28.3)	13 (27.7)	58 (28.4)	0.99
Postprocedure stent placement, n (%)	219 (87.3)	43 (91.5)	176 (86.3)	0.46
Duration of operation (minutes), mean ± SD	60.5 ± 19.6	54.6 ± 13.7	61.8 ± 20.5	0.02

Prestenting was performed due to unsuccessful instrumentation of the ureteral orifice in 36 of the 47 (76.6%) of the cases. In rest of the 11 patients, prestenting was performed due to severe hydronephrosis (n = 3), renal colic (n = 6), or febrile urinary tract infection (n = 2).

Success rates

Successful results were established in 202 of the 251 (80.5%) patients. Prestented group was shown to have a higher success rate compared with the nonprestented group (43 of the 47 patients [91.5%] vs 159 of the 204 patients [77.9%], p = 0.04). In patients with ureteral stones, the success rate of the prestented group was found to be significantly higher compared with the nonprestented group (32 of the 34 patients [94.1%] vs 116 of the 146 patients [79.5%], p = 0.04); however, success rates of the groups were found to be similar in case of renal stones, although a propensity in favor of prestenting was observed (11 of the 13 patients [84.6%] vs 43 of the 58 patients [74.1%], p = 0.72). Results of the success rates are summarized in Figure 1.

FIG. 1.

Success rates of the prestented and nonprestented groups.

In univariate analysis, the presence of multiple stones (p = 0.04) and stone size (p = 0.01) were identified as the other parameters associated with decreased success rate in the entire population and in case of ureteral stones in addition to prestenting. In case of renal stones, stone location in a lower calyx (p = 0.001) and stone size (p = 0.01) were identified as parameters associated with decreased success rates. These parameters were involved in multivariate models for the entire population, ureteral stone cases, and renal stone cases separately. Prestenting (odds ratio [OR]: 1.592; 95% confidence interval [CI]: 1.105, 4.78; p = 0.04) and smaller stone size (OR: 2.81; 95% CI: 1.445, 6.140; p = 0.02) were identified as independent predictors of success in the entire population. Similarly, in case of ureteral stones, prestenting (OR: 1.66; 95% CI: 1.111, 5.027; p = 0.04) and smaller stone size (OR: 2.66; 95% CI: 1.405, 5.882; p = 0.03) were identified as independent predictors of success. In case of renal stones, only stone location (out of lower calyx) was identified to be an independent predictor of success. The results of multivariate analysis are summarized in Table 2.

Table 2.

Results of Multivariate Analysis to Determine Factors Associated with Success Rates

Parameter	OR	95% CI	p-Value
Entire cohort
Prestenting	1.592	1.105, 4.788	0.04
Stone size	2.813	1.445, 6.140	0.02
Ureteral stones
Prestenting	1.661	1.111, 5.027	0.04
Stone size	2.664	1.405, 5.882	0.03
Kidney stones
Stone size	1.258	0.658, 2.887	0.56
Stone location (vs lower calyx)
Middle calyx	4.566	1.988, 7.102	0.001
Upper calyx	4.808	2.016, 8.554	0.001
Renal pelvis	5.226	2.336, 9.112	0.001

CI = confidence interval; OR = odds ratio.

Separate analysis with respect to stone size revealed that beneficiary effect of prestenting mainly applies to patients with stones >7 mm. In the subgroup of patients with stones ≤7 mm, the success rates of prestented and nonprestented groups were 92.8% and 94.5%, respectively (p = 0.58). However, in patients with stones >7 mm, the success rate of the prestented group was significantly higher than the nonprestented group (30 of 33 patients [90.9%] vs 73 of the 113 [64.6%], p = 0.004).

Complication rates

Totally, complications were recorded in 34 (13.5%) patients in the entire cohort. In the prestented and nonprestented groups, 4 of the 47 patients (8.5%) and 30 of the 204 (14.7%) developed complications, respectively (p = 0.347). Complication rates of the two groups with respect to Clavien grades are summarized in Table 3. We also evaluated the effect of prestenting on the complication rates in the renal and ureteral stone patients separately. In the ureteral stone patients group, complications developed in 3 of the 34 (8.8%) and 25 of the 146 (17.1) prestented and nonprestented patients, respectively. The difference was statistically nonsignificant (p = 0.29). In the renal stone patients group, complications developed in 1 of the 13 (7.7%) and 5 of the 58 (8.6) prestented and nonprestented patients, respectively. The difference was also statistically not significant (p = 0.99).

Table 3.

Complication Rates of the Two Groups with Respect to Clavien Grading System

Clavien grade	Whole population (n = 251)	Prestented group (n = 47)	Nonprestented group (n = 204)	p-Value
Grade I, n (%)	17 (6.7)	1 (2.1)	16 (7.8)	0.347
Grade II, n (%)	12 (4.8)	2 (4.2)	10 (4.9)
Grade III, n (%)	5 (2.0)	1 (2.1)	4 (1.9)
Grade IV and V	—	—	—
Total, n (%)	34	4 (8.5)	30 (14.7)

Discussion

There is growing evidence in favor of prestenting before URS procedures in terms of increasing success rates and decreasing complication rates.^{6

–14} Therefore, the debate continues on the topic, whether these potential benefits outweigh the disadvantages of an additional procedure. However, almost all of the studies evaluating the role of prestenting are from an adult population and the current study is the first one to compare prestented and nonprestented groups in a pediatric population. Our results indicate that prestenting may improve the success rates of pediatric URS procedures.

Our results from the entire cohort in terms of success rate (80.5%) and complication rate (13.5%) are parallel to the findings of previously published pediatric URS series that report success rates of 58% to 98% and complication rates of 0% to 22.7%.^18

–22 A recent review of pediatric URS studies points out the global nonuniformity of prestenting behavior in pediatric cases and mentioned a mean rate of 47% (range: 0%–100%) prestenting, which is higher than the 18.7% rate of prestented patients in our study.²³

The evidence in favor of prestenting began to be established as early as 1990. Jones and colleagues²⁴ evaluated the role of prestenting in cases of failed URS retrospectively in 42 patients and found that ureteral stent insertion was associated with improved outcomes in the subsequent procedure. Hubert and Palmer were the first to evaluate the role of prestenting in the pediatric population. The authors evaluated the data of 26 patients who failed ureteral access in the first procedure, with a median age of 10.3 years, and found that passive dilation with a ureteral stent rules out the need for active dilation, and is a safe procedure.⁷ However, this study neither provided detailed information on the success rates of the procedures nor comparative results with a nonprestented population.

The first comparative study of prestented patients with a nonprestented group was performed by Rubenstein et al. In this study, 36 of the 115 renal units were prestented and success rates (defined as fragments ≤2 mm) were found to be significantly higher in the prestented group (54% vs 78%, p < 0.02). However, no differences in the complication rates were reported.¹³ Later on, Shields and colleagues reported their results of prestented patients (n = 150) in comparison with the nonprestented (n = 71) group and reported an 86.9% overall success rate after a single procedure. A positive association of prestenting and success rates was observed, but the difference was not statistically significant (88.7% vs 83.1%, p = 0.254). In this study, stone size and stone burden were found to be associated with success rates.¹⁴

Due to the conflicting results on the effect of prestenting in terms of stone clearance rates, further research focused on identification of particular patient groups with respect to stone size or location that would benefit from prestenting. In one of the studies focusing on stone size, Chu and colleagues detected similar stone clearance rates comparing the prestented and nonprestented patients. However, prestenting was found to be associated with shorter operative times and less need for secondary procedures in cases of stones >1 cm.⁶ Another study focusing on stone size was performed by Kawahara et al.⁹ and prestenting was found to be associated with better stone clearance rates in a population of patients with stones >1.5 cm. Netsch and colleagues¹² matched the 143 prestented patients with a nonprestented group of 143 patients and evaluated the stone clearance rates with respect to stone size and results showed that prestenting increased the stone-free rates only in patients with stones >5 mm. In our study, we performed separate analysis with 7-mm cutoff for the stone size and parallel to the findings of the previous studies, the effect of prestenting was prominent in patients with larger stones. We also identified an inverse relationship between stone size and success rates and prestenting seems to mitigate the negative effect of stone size on success rates.

With respect to stone location, another important parameter dealing with success rates of URS, some studies established valuable information on the role of prestenting. In a recent study, Lumma and colleagues compared the data of 486 prestented patients with 64 nonprestented patients. The results pointed out the beneficial effect of prestenting on stone-free rates in cases of proximal ureteral stones, but not the distal ones.¹⁰ In our study, stone location was not identified as a predictor of success in the ureteral stone cases and success rates for stones located in the upper, middle, or lower ureter were similar (data not provided). However, in case of kidney stones, stone location in a lower calyx was significantly associated with lower success rates in the multivariate analysis compared with other calyx or renal pelvis locations.

Mueller et al.¹¹ performed separate analysis for subgroup of ureteral stone cases and detected higher stone-free rates when the patient was prestented. However, in a more recent trial, Jessen and colleagues also focused on stone location and performed separate analysis for renal and ureteral cases. According to their results, prestenting increased the success rates in kidney stone cases, but not in ureteral stone cases.⁸ Similarly, in another recent study, Assimos and colleagues¹⁵ detected increased stone-free rate with prestenting in renal stone cases, but not in ureteral stone cases. Our results also indicate that prestenting increases the success rates in ureteral stone cases parallel to the results of Mueller et al.,¹¹ but contrary to Jessen et al.⁸ and Assimos et al.¹⁵ We could not identify significant difference in success rates with respect to prestenting in kidney stone cases. This finding seems to be contrary to the findings of previous studies,^{8

–13,15} but we think that this is possibly due to the relatively lower number of prestented patients who underwent URS for a kidney stone (n = 13) in our study. This low number of cases diminishes the power of study to identify the significant difference between 84.6% and 74.1% success rates of prestented and nonprestented cases, respectively. We also determined the success rate with respect to surgeons' decision of absence of stones >2 mm at the end of procedure rather than postoperative imaging, which may deal with the success rates and effect of prestenting as well.

Previously published studies also show diverse results with respect to effect of prestenting on complication rates. This is possibly related to nonuniformity in reporting of complications, the presence of other factors associated with complications, and retrospective nature of the studies. Rubenstein and colleagues¹³ reported totally eight complications in their 115 procedures and ureteral stricture was found to develop in one patient in each of the prestented and nonprestented groups. Netsch et al.¹² classified the complications according to the Clavien system and reported a total complication rate of 9.5% without a significant difference with respect to prestenting.

Contrary to these findings, Lumma and colleagues¹⁰ reported their complications classified as minor and major, with the prestented group having fewer complications in both classes compared with the nonprestented patients. Similarly, Mueller et al.¹¹ found lower complication rates in ureteral stone patients with prestenting. Jessen et al. detected complication rates of 6.5% and 14.5% for the prestented and nonprestented groups, respectively (p = 0.003). The authors also analyzed kidney and ureteral stone cases separately and prestenting was found to be associated with fewer complications in both locations.⁸ However, Assimos et al.¹⁵ reported decreased complication rates in renal stone patients, but not in ureteral stone patients. Our complication rate of 13.5% is parallel to the results of these studies as well as results of previous pediatric URS series. We classified the complications according to the modified Clavien system and the prestented group was found to have lower complication rates (8.5%) compared with the nonprestented group (14.5%), but the difference was statistically insignificant (p = 0.347). This is also possibly related to insufficient power due to lower number of cases. When we performed subgroup analysis for complication rates of the renal and ureteral stone patients, prestenting was not found to be associated with decreased complication rates in both subgroups. Additionally, surgeon's experience, preoperative indications, and quality of equipment are important parameters that affect incidence of complications.²⁵ Our institution is an educational center, therefore variations in surgeons' experience may have an effect on the complication rates beyond the effect of prestenting.

Our study has several limitations. Retrospective nature is the most important limitation. Lacking a prospectively assigned control group pulls the disadvantage of selection bias. The most common indication for prestenting was unsuccessful instrumentation, which also makes the selection bias obvious. Additionally, we evaluated the success rate with allowance of <2-mm residual fragments rather than complete stone-free status. This was due to the fact that stone dusting is the preferred method of fragmentation in our institution and collection of the fragments is not routinely performed and limited to sampling for stone analysis. Another important limitation is the lower number of prestented cases compared with the control group. This possibly makes the study underpowered to show the significant differences of success rates and complication rates especially in the subgroup analysis. We also did not evaluate the possible disadvantages related to prestenting such as additional anesthesia, cost, and stent-related symptoms due to retrospective nature of the study.

Despite abovementioned limitations, our study still provides unique information on the effect of prestenting in pediatric URS outcomes. During clinical decision-making, the need of additional general anesthesia, hospitalization, radiation exposure, additional costs, and stent-related symptoms should also be kept in mind. Ureteral stenting, although a simple procedure, can even lead to ureteral obstruction in the pediatric age group.²⁶ Based on our results, we cannot recommend routine prestenting unless the patient presents with pyelonephritis. Most of our prestented cases were stented due to difficult access, instead of routine prestenting. However, with the confidence of higher success rates in the subsequent procedure, it seems reasonable to inform the patient and/or parents, take the patient to the operating room with intent to treat instead of prestenting, and insert a stent in case of failure. By this way, it would be possible to avoid disadvantages of the additional procedure, while retaining the possible benefits of prestenting in terms of success and complication rates.

Conclusions

This study is the first to evaluate the effect of prestenting on outcomes of URS in the pediatric population. Prestenting was found to increase the success rate of the procedure especially in cases of larger stones and ureteral stones. Prestenting also provided lower complication rates, but the difference was not significant. We cannot recommend routine prestenting in pediatric cases based on the results of the current study, and it seems a good option to try to treat the patient in the first session without prestenting and retain the advantages of prestenting to the subsequent procedure in case of failed URS.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

References

Mandeville

, Nelson

. Pediatric urolithiasis. Curr Opin Urol, 2009; 19:419–423.

Smaldone

, Cannon

Jr. , Wu

, et al. Is ureteroscopy first line treatment for pediatric stone disease?. J Urol, 2007; 178:2128–2131; discussion 31.

Lahme

. Shockwave lithotripsy and endourological stone treatment in children. Urol Res, 2006; 34:112–117.

Satar

, Zeren

, Bayazit

, Aridogan

, Soyupak

, Tansug

. Rigid ureteroscopy for the treatment of ureteral calculi in children. J Urol, 2004; 172:298–300.

de la Rosette

, Denstedt

, Geavlete

, et al. The clinical research office of the endourological society ureteroscopy global study: Indications, complications, and outcomes in 11,885 patients. J Endourol, 2014; 28:131–139.

Chu

, Sternberg

, Averch

. Preoperative stenting decreases operative time and reoperative rates of ureteroscopy. J Endourol, 2011; 25:751–754.

Hubert

, Palmer

. Passive dilation by ureteral stenting before ureteroscopy: Eliminating the need for active dilation. J Urol, 2005; 174:1079–1080; discussion 80.

Jessen

, Breda

, Brehmer

, et al. International collaboration in endourology: Multicenter evaluation of prestenting for ureterorenoscopy. J Endourol, 2016; 30:268–273.

Kawahara

, Ito

, Terao

, et al. Preoperative stenting for ureteroscopic lithotripsy for a large renal stone. Int J Urol, 2012; 19:881–885.

10.

Lumma

, Schneider

, Strauss

, et al. Impact of ureteral stenting prior to ureterorenoscopy on stone-free rates and complications. World J Urol, 2013; 31:855–859.

11.

Mueller

, Riechert-Muhe

, Schrader

, et al. Einfluss der Ureterschienung vor ureterorenoskopischer Behandlung von Harnleitersteinen [Influence of ureter stenting before ureterorenoscopic treatment of ureteral calculi]. Urol A, 2014; 53:1656–1660.

12.

Netsch

, Knipper

, Bach

, Herrmann

, Gross

. Impact of preoperative ureteral stenting on stone-free rates of ureteroscopy for nephroureterolithiasis: A matched-paired analysis of 286 patients. Urology, 2012; 80:1214–1219.

13.

Rubenstein

, Zhao

, Loeb

, Shore

, Nadler

. Prestenting improves ureteroscopic stone-free rates. J Endourol, 2007; 21:1277–1280.

14.

Shields

, Bird

, Graves

, Gomez-Marin

. Impact of preoperative ureteral stenting on outcome of ureteroscopic treatment for urinary lithiasis. J Urol, 2009; 182:2768–2774.

15.

Assimos

, Crisci

, Culkin

, et al. Preoperative JJ stent placement in ureteric and renal stone treatment: Results from the Clinical Research Office of Endourological Society (CROES) ureteroscopy (URS) Global Study. BJU Int, 2016; 117:648–654.

16.

Turk

, Petrik

, Sarica

, et al. EAU Guidelines on interventional treatment for urolithiasis. Eur Urol, 2016; 69:475–482.

17.

Dindo

, Demartines

, Clavien

. Classification of surgical complications: A new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg, 2004; 240:205–213.

18.

Bassiri

, Ahmadnia

, Darabi

, Yonessi

. Transureteral lithotripsy in pediatric practice. J Endourol, 2002; 16:257–260.

19.

Minevich

, Defoor

, Reddy

, et al. Ureteroscopy is safe and effective in prepubertal children. J Urol, 2005; 174:276–279; discussion 9.

20.

Tanriverdi

, Silay

, Kendirci

, et al. Comparison of ureteroscopic procedures with rigid and semirigid ureteroscopes in pediatric population: Does the caliber of instrument matter?. Pediatr Surg Int, 2010; 26:733–738.

21.

Turunc

, Gonen

, Kuzgunbay

, et al. The effects of hydronephrosis and stone burden on success rates of shockwave lithotripsy in pediatric population. J Endourol, 2010; 24:1037–1041.

22.

Dogan

, Onal

, Satar

, et al. Factors affecting complication rates of ureteroscopic lithotripsy in children: Results of multi-institutional retrospective analysis by Pediatric Stone Disease Study Group of Turkish Pediatric Urology Society. J Urol, 2011; 186:1035–1040.

23.

Ishii

, Griffin

, Somani

. Ureteroscopy for stone disease in the paediatric population: A systematic review. BJU Int, 2015; 115:867–873.

24.

Jones

, Ryan

, Lyons

, Grainger

, McDermott

, Butler

. Use of the double pigtail stent in stone retrieval following unsuccessful ureteroscopy. Br J Urol, 1990; 66:254–256.

25.

Esposito

, Mattioli

, Monguzzi

, et al. Complications and conversions of pediatric videosurgery: The Italian multicentric experience on 1689 procedures. Surg Endosc, 2002; 16:795–798.

26.

Escolino

, Esposito

, Farina

, et al. Iatrogenic ureteral obstruction in pediatric age: An unusual complication of ureteral stenting. Minerva Urol Nefrol, 2014; 66:286–287.