Semi-Rigid Ureteroscopy Should Not Be the First Option for Proximal Ureteral Stones in Children

Abstract

Purpose:

To investigate the factors that predict the success and complication rates of semi-rigid ureteroscopy (URS) in pediatric population.

Materials and Methods:

This is a retrospective analysis of the database including 182 patients who underwent URS between 2001 and 2016. The possible factors that might affect the outcome were age, gender, stone laterality, largest stone size, number of stones, stone location, orifice dilatation status, and caliber of ureteroscope.

Results:

The mean age was 68.1 (7–204) months, and male-to-female ratio was 94:88. Operative side was left for 97, right for 82, and bilateral for 3 patients. One hundred and forty-four patients had a single stone, and 38 patients had multiple stones. The median largest stone size was 7 (2–20) mm. Postoperative ureteral stenting was performed in 150 (86.2%) patients. The overall success rate was 84.6%, while 81.6% and 85.4% in 8F URS and 4.5F URS groups, respectively (p = 0.560). Stone-free rate was higher among patients who were older than 36 months, distal ureteral stones and single stones (p = 0.012, 0.002, and 0.009, respectively). Complication rate was higher for proximally located stones (p = 0.029). The mean follow-up was 23.9 ± 32.5 months.

Conclusion:

URS is a safe procedure with acceptable success rates in the pediatric population. Younger age, multiple stones, and proximal location are the predisposing factors for failure, whereas proximal location was the only factor for complication occurrence. Therefore, semi-rigid ureteroscopy should not be the first choice in the treatment of proximal ureteral stones, and alternative methods should be preferred, if available.

Introduction

In recent years, pediatric stone disease prevalence has increased due to the widespread use of ultrasonography, dietary habits, and sedentary life styles.¹ Pediatric stone disease is endemic in Turkey, and the incidence of pediatric stone disease is also increasing in the Western world.² During the past 25 years, the incidence of nephrolithiasis in children has increased by ∼6% to 10% per year.³ Minimally invasive procedures have become more important with the development of endoscopic equipment, improvement in surgical techniques, and experience. Before the availability of flexible instruments, the rigid and semi-rigid ureteroscopes were the only minimally invasive surgical modality for ureteric stones that was probably being used with an extended indication in any location for both adults and children. Within time, indications, limitations, and predictive factors for complications have been better understood.⁴ Despite the inclusion of flexible instruments to pediatric age group, the semi-rigid ones still play an important role in endourological ureteral stone treatment. However, as the stone is placed proximally, the semi-rigid instrument has the risk of traumatizing the ureteral orifice and complications regarding increased intrarenal pressure. Thus, we hypothesized that proximal ureteral stones have decreased stone-free and increased complication rates. Besides, we also aimed to evaluate other predictive factors for success and complications of semi-rigid ureteroscopy (URS) in pediatric population from a single-institute experience.

Materials and Methods

This is a retrospective analysis of a database including 182 patients who had undergone URS between 2001 and 2016. Investigated possible factors that might affect outcome were age, gender, stone laterality, largest stone size, number of stones, stone location, orifice dilatation, and caliber of ureteroscope.

Preoperative urine culture and analysis were carried out in all patients, and those with positive urine cultures were treated before the procedure. All procedures were performed under general anesthesia and antibiotic prophylaxis using 8F or 4.5F ureteroscopes. Before 2014, only 8F ureteroscope (Karl Storz, Tuttlingen, Germany) was available in our clinic, while 4.5F URS (Richard Wolf GmBH, Knittlingen, Germany) began to be used in our procedures after 2014. Before URS, all patients were placed a safety guidewire (0.035F), and then the ureteroscope was inserted into the ureter. Hydro-dilatation with a manual pump method was applied for all patients. Active dilatation by a balloon or coaxial dilatator was used when hydro-dilatation failed. Isotonic liquid in body temperature has been used for irrigation. After the stone was reached, laser or pneumatical lithotripter was used. After fragmentation by pneumatic or laser, stones were removed with a forceps or left for spontaneous passage depending on the surgeon's preference. After removal, a Double-J stent (DJS) or ureter catheter was inserted into the ureter. Postoperative complications were classified based on the Clavien–Dindo system. The stone-free status after single procedure was initially evaluated 2 weeks after stent removal using ultrasonography (USG) plus KUB (kidney, ureter, and bladder radiograph), and non-contrast CT was used in cases of clinical or radiological uncertainty. The presence of any residual fragment was regarded as failure. We did not routinely perform voiding cystourethrography (VCUG) or scintigraphic studies to evaluate the status of vesicoureteral reflux or ureteral stricture. These kinds of studies were spared for cases with sustaining, progressive hydronephrosis and/or symptomatic cases in the long term.

Statistical analyses were performed using SPSS, version 17.0. Mann–Whitney, chi-squared, and t-tests were used when appropriate, and logistic regression analysis was used for multivariate analysis. A p value <0.05 indicated statistical significance.

Results

The mean age was 68.1 ± 46.3 months (7–180), and male-to-female ratio was 94:88. Operative side was left in 97, right in 82, and bilateral in 3 patients. One hundred and forty-four patients had a single stone, and 38 patients had multiple stones. The median largest stone size was 7.44 ± 3.4 mm (3–20). The mean follow-up was 23.9 ± 32.5 months. Fifty-four (29.6%) patients were followed >24 months, and 81 (44.5%) patients were followed >12 months.

A DJS or ureteral catheter was inserted postoperatively in 89.6% of patients, while no diversion was placed in 10.4%. The ureter catheters were removed on the first postoperative day, while the removal of DJS was performed after a median of 4 (1–15) weeks.

Stone fragmentation was performed by laser in 73.6% (n = 134) and by pneumatic lithotripter in 15.4% (n = 28). The stone was removed using basket or forceps-only in 11% without any lithotripsy method.

The overall success rate was 84.6% after single procedure. The success rate was 81.6% in 8F URS group and 85.4% in 4.5F URS group (p = 0.560) (Table 1). Stone-free rate was significantly related to age (receiver operating characteristic [ROC] curve for 36 months; 79% sensitivity; 47% specificity; area under curve, 0.620), stone location (upper ureter), and number of stones (p = 0.012, 0.002, and 0.009), respectively. Multivariate analysis showed that age, stone location, and number of stones were the independent prognostic factors for stone-free status (Table 2). The URS caliber did not affect success rate in these age groups (success rates 4.5F vs 8F: ≥36 months: 85.7% vs 89.1%; p = 0.618; <36 months: 70% vs 73.5%; p = 0.826). Shock-wave lithotripsy (SWL) was performed on 6 patients (3.3%), and re-URS was performed on 19 (10.4%) as a second procedure.

Table 1.

Comparison of Perioperative Factors Based on Ureteroscope Size

Factors	Overall	4.5F	8F	p^a
Age (months), mean ± SD	68.1 ± 46.3	61.9 ± 41.4	69.8 ± 47.5	0.491
Success, n (%)	154 (84.6)	31 (81.6)	123 (85.4)	0.560
Complication, n (%)	11 (6)	0 (0)	11 (7.6)	0.127
Stone size (mm), mean ± SD	7.44 ± 3.4	6.4 ± 2.7	7.6 ± 3.5	0.095
Gender, n (%)
Female	88	15 (60.5)	73 (50.7)	0.218
Male	94	23 (39.5)	71 (49.3)	0.218
Side, n (%)
Right	82	15 (39.5)	67 (46.5)	0.669
Left	97	22 (57.9)	75 (52.1)
Bilateral	3	1 (2.6)	2 (1.4)
No. of stones, n (%)
Single	144	27 (71.1)	117 (81.3)	0.169
Multiple	38	11 (28.9)	27 (18.8)	0.169
Location of stone, n (%)
Upper	33	6 (15.8)	27 (18.8)	0.674
Lower	149	32 (84.2)	117 (81.2)	0.674
Type of fragmentation, n (%)
Laser	134	32 (84.2)	102 (70.8)	0.140
Pneumatic	28	2 (5.3)	26 (18.1)	0.140
Active ureteral orifice dilatation, n (%)
Yes	13	2 (5.2)	11 (7.6)	0.613
No	169	36 (94.8)	133 (92.4)	0.613

univariate analysis.

SD = standard deviation.

Table 2.

Preoperative Factors Affecting the Stone-Free Rates

	Stone-free (n), %	p^a	p^b
Age
<36 months	(32) 72.7	0.012	0.010
≥36 months	(122) 88.4	0.012	0.010
Gender
Female	(77) 87.5	0.298
Male	(77) 81.9	0.298
Side
Right	(71) 86.6	0.321
Left	(82) 84.5	0.321
No. of stones
Single	(127) 88.2	0.009	0.015
Multiple	(27) 71.1	0.009	0.015
Location of stone
Upper	(22) 66.7	0.002	0.014
Lower	(132) 88.6	0.002	0.014
Type of ureteroscope
4.5F	(31) 81.6	0.561
8F	(123) 85.4	0.561
Stone size
≤7 mm	(93) 84.5	0.974
>7 mm	(61) 84.7	0.974
Type of fragmentation
Laser	(111) 82.8	0.710
Pneumatic	(24) 85.7	0.710
Active ureteral orifice dilatation
Yes	(10) 76.9	0.425
No	(144) 85.2	0.425

Chi-square test.

Multivariate (binary logistic regression).

No complication occurred after the procedures that used 4.5F ureteroscope, while complications developed in 11 (Clavien 1:10 postoperative pyelonephritis; Clavien 3:1 intraoperative ureteral perforation) patients (7.6%) after the procedures that used 8F ureteroscope; however, the difference was not statistically significant (p = 0.127). Ureteral perforation was recognized intraoperatively and treated using a DJS placement; in addition, postoperative pyelonephritis was treated using intravenous antibiotics. Complication rate was associated with stone location (p = 0.029) (Table 3). Within the follow-up period, no sustaining, progressive, or symptomatic hydronephrosis was detected; therefore, the possibility of reflux or stricture was not evaluated further.

Table 3.

Factors Affecting the Complication Rates

	Complication (n), %	p^a
Age
<36 months	(3) 6.8	0.805
≥36 months	(8) 5.8	0.805
Gender
Female	(5) 5.7	0.843
Male	(6) 6.4	0.843
Side
Right	(4) 4.9	0.604
Left	(7) 7.2	0.604
No. of stones
Single	(10) 6.9	0.322
Multiple	(1) 2.6	0.322
Location of stone
Upper	(5) 15.2	0.016
Lower	(6) 4	0.016
Type of ureteroscope
4.5F	(0) 0	0.127
8F	(11) 7.6	0.127
Stone size
≤7 mm	(8) 7.3	0.391
>7 mm	(3) 4.2	0.391
Type of fragmentation
Laser	(8) 6	0.815
Pneumatic	(2) 7.1	0.815
Active ureteral orifice dilatation
Yes	(1) 7.7	0.796
No	(10) 5.9	0.796
Urinary diversion
Yes	(18) 10.5	0.880
No	(1) 9.1	0.880

Univariate analysis by chi-squared test.

Discussion

In recent years, depending on technological developments, endoscopic instruments have become smaller in size and are being used more often on children. Although technically identical to adult URS, smaller endoscopic instruments, probes, and lithotripters seem more useful in pediatric patients.^5
–7 It was reported that endoscopic treatment of ureteral stones in children did not lead to significant reflux or stenosis.^8,9

As the instruments used in URS get smaller in size, some studies were designed to compare current success and complication rates. There is controversial data concerning adults' and children's cases in the literature. When comparing 8F and 6.9F ureteroscopes, Tanrıverdi and colleagues reported that the difference in size did not affect success rates.¹⁰ Atar and colleagues reported that 4.5F ureteroscope had greater success rates than 7.5F ureteroscope on children between 0 and 3 years.¹¹ In our study, there was no significant difference between 4.5F and 8F ureteroscopes in terms of success rates (85.4% vs 81.6%). Moreover, the size of the instrument did not change the stone-free rate for different age groups (≥36 vs <36 months). There was also no significant difference between the lithotripters in terms of success rates (laser vs pneumatic: 82.8% vs 85.7%). It supports the fact that as it is possible to insert the instrument into the ureter, the size of the instrument is not important in terms of success. Owing to the availability of laser probes, the relatively narrow working channel of 4.5F ureteroscope does not preclude adequate vision and flow of irrigation fluid.

In recent literature, ureteroscopy is used in the treatment of ureteral stones in children with high success rates of 58% and 100%.^{4,6,10,12
–14} In our study, the overall success rate was 84.6% and in accordance with the literature. Unfavorable factors affecting the success were <3 years of age, having multiple stones, and stone location at the upper ureter. Multiple stones and proximal ureteral stones extend the duration of the process and cause failure due to push-back or inability to reach.

Atar and colleagues reported that the success rate of 4.5F ureteroscope in 0–3-year-old patients was higher than 7.5F ureteroscope.¹¹ In our study, the success rate in patients >3 years of age was found to be higher than other age groups. The ureteroscope calibration used in these age groups did not affect success rate. Although instruments with lower calibration appear to be statistically not affecting the complication rates (0% vs 7.6%; p = 0.127), it is remarkable that there was no complication detected by these instruments. This statistical indifference may be attributed to the disproportional number (38 in 4.5F and 144 in 8F groups) of patients in compared groups. In contrast, a semi-rigid ureteroscope in large diameter carries the potential risk for trauma of the ureteral orifice by causing mucosal tears which may lead to further stricture or reflux. Moreover, the surgeon should not forget the fact that, even when using thin instruments, the size of the ureteroscope gets larger from tip to hand-holder side, which means a higher trauma risk to the orifice when attempting to reach proximal ureteral stones.

Various intraoperative and postoperative complications of URS include hematuria, pyelonephritis, urinary retention, urethral stone, stone migration, and ureteral perforation. In the literature, complication rates of URS were reported to range from 0% to 19.2%, and it was 6% in our series.^7,15,16 One of these patients developed intraoperative ureteral perforation; so the procedure was terminated and a DJS was placed. The other patients developed pyelonephritis. Dogan and colleagues detected prolonged operational time as an independent factor affecting the complications.⁴ Because of the retrospective nature of our study, we were not able to analyze the effect of operation duration on complication rate. Alternatively, proximal ureteral location of the stone was found to be a factor affecting the complication rate, which possibly reflects the relatively increased intrarenal pressure when working with proximal ureter. The larger calibration of the ureteroscope at the bottom enforces the ureter to be exposed to trauma, resulting in the penetration of microorganisms after mucosal injury. Another possible mechanism may be the decreased backflow due to decreased intraluminal space around the larger ureteroscope. For this reason, larger-sized rigid ureteroscopes should not be used, and less traumatic flexible ureteroscopes or antegrade percutaneous approaches should be preferred as the first choice in the treatment of upper ureteral stones.

Active ureteral orifice dilatation before URS depends on the choice of the surgeon, and it is controversial. In the literature, active dilatation of the orifice ranges between 0% and 100%.^7,10,14,16 This ratio was 7.1% in our series. Although our expectation was better success and complication rates favoring the hydrodilatation, we detected similar success and complication rates between active and hydro-dilatation groups. This indifference can be attributed to the very small number (only 13) of patients in active dilatation group. Despite this finding, we still recommend hydro-dilatation, which is less invasive than balloon or coaxial dilatation.

Stent placement after URS is also controversial; the ratio is reported as 13% and 100% in the literature.^4,7,10,17,18 In our series, DJS was placed in 86.8% of patients and ureteral catheter in 2.7% of patients. Both DJS and ureteral catheter prevent possible complications by preventing postoperative edema and hydronephrosis. The choice of DJS or ureteral catheter placement is based entirely on the surgeon's preference and course of the surgery.

Because of the abovementioned factors, semi-rigid ureteroscope does not seem to be the first and best option for proximal ureteral stones. In terms of supporting our findings, the AUA guidelines recommend clinicians to have a flexible instrument readily available if they plan to treat a proximal ureteral stone,¹⁹ and the Clinical Research Office of the Endourological Society (CROES) study reported that ureteroscopy for proximal stones using semi-rigid instruments have higher failure and retreatment rates than the flexible ones.²⁰ Although there is no information regarding children, for adults, flexible ureteroscopy had better stone-free rates than semi-rigid instruments for proximal ureteral stones.^21,22 Therefore, if the surgeon prefers to use a flexible ureteroscope in a child, placing a ureteral access sheath (UAS) of 11.5F outer diameter as in adults will not always be possible for every age, and performing a surgery without UAS carries the risk of increasing intrapelvic pressure and shortening the lifespan of the instrument. SWL may be an option; yet, the resistance of certain stone types, radiolucency of some stones, and need for using fluoroscopy for focusing are the limiting factors. Antegrade approaches have the advantage of justifying possible ureteral orifice complications; it carries all well-known risks of percutaneous renal surgery. All these factors should be considered during decision making when treating a proximal ureter stone.

Due to the retrospective nature of our study, the lack of randomization might have caused a selection bias among the groups. Owing to the fact that our department is in a training hospital and has the formation of different experienced surgeons at different times, this can affect success and complication rates. Some important data, such as the duration of operations, body weight, and height measurements, could not be obtained entirely; accordingly, this led to an inability to analyze the effects of these factors on complications and success rates.

Conclusion

Semi-rigid URS is a feasible and safe procedure in pediatric population. It is important to consider that some factors may lead to failure and complications. The use of appropriate-sized instruments is of utmost importance to avoid complications. Semi-rigid ureteroscopy should not be the first choice in the treatment of proximal ureteral stones due to decreased stone-free and increased complication rates; alternative methods should be preferred, if available.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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