Comparison of Retrograde Intrarenal Surgery and Micro-Percutaneous Nephrolithotomy in Moderately Sized Pediatric Kidney Stones

Abstract

Purpose:

To compare the effectiveness and reliability of retrograde intrarenal surgery (RIRS) and micro-percutaneous nephrolithotomy (micro-perc) for the management of kidney stones in pediatric patients.

Materials and Methods:

A retrospective analysis was made of pediatric patients aged <18 years with kidney stones that ranged from 10 to 20 mm in size, who underwent RIRS (n = 36) or micro-perc (n = 45) in referral centers.

Results:

In the RIRS group, the mean age of patients was 8.39 ± 4.72 years and in the micro-perc group, it was 5.62 ± 4.50 years (p = 0.01). The mean stone size was 12.80 ± 3.03 mm in the RIRS group and 13.97 ± 3.46 mm in the micro-perc group (p = 0.189). The success rate was 86.2% (n = 31) in the RIRS group and 80.0% (n = 36) in the micro-perc group (p = 0.47). The mean complication rate was 16.6% and 13.3% in the RIRS and micro-perc groups, respectively (p = 0.675). Hospital stay and radiation exposure were significantly lower in the RIRS group (all p < 0.001). The mean anesthesia session was 1.94 in the RIRS group and 1.26 in the micro-perc group (p < 0.001). The mean hemoglobin drop was 0.53 ± 0.87 g/dL in the micro-perc group, and none of the cases required blood transfusion.

Conclusion:

The results of this study suggested that micro-perc and RIRS were highly effective methods for the treatment of moderately sized renal stones in children, with comparable success and complication rates. Patients and their parents should be informed about the currently available treatment options, and of their efficacy and safety. However, further clinical trials are needed to support these results.

Introduction

Pediatric kidney stone disease is a significant health problem throughout the world, and particularly in endemic regions, including Turkey, its prevalence has been increasing.^1,2 In a pediatric patient group, the aims of urinary stone disease treatment are removal of the stone, prevention of recurrences and urinary tract infections, preservation of kidney functions, and correction of the anatomical and underlying metabolic problems. Miniaturization of the endoscopic instruments, advancements in optical systems, availability of intra-corporeal lithotripters, increased surgical experience, and low complication rates have made dramatic changes in the treatment of pediatric kidney stone disease in recent years. Kidney stones that could previously only be treated with surgery can now be treated with various minimally invasive techniques.³

Current guidelines recommend extracorporeal shockwave lithotripsy (SWL) as the first treatment option in pediatric kidney stones that are smaller than 2 cm.³ However, there are disadvantages, including the need for multiple sessions, general anesthesia requirement, lower success rates in bigger stones, and unknown long-term effects of the shock waves on the developing kidney.^4
–6 For larger (>2 cm) and complex pediatric kidney stones, percutaneous nephrolithotomy (PNL) has been recommended as the first-line treatment.³ Although this treatment method is distinguished from other treatment modalities with very good stone-free rates in the treatment of particularly larger kidney stones, it may present problems in children because of the smaller size of the kidneys and collecting systems, friable renal parenchyma, and mobility of the pediatric kidney.

The first pediatric PNL procedure was performed by Woodside et al.,⁷ by using the equipment used in adults. Later, it was predicted that a decrease in the tract diameter would cause less parenchymal and vascular injury, and a mini-PNL method was established, by using instruments with smaller diameters in selected patients.^8,9 Decreasing the diameter of the working sheath attracted great attention, and “micro-percutaneous nephrolithotomy” (micro-perc) or, as it was originally called, the “all-seeing needle” term was introduced.^10,11 Thereafter, a number of studies reported the feasibility and safety of micro-perc in both adults and children.^11

–14

Current guidelines do not recommend another minimal invasive treatment option, retrograde intrarenal surgery (RIRS), as the first-line treatment option in pediatric kidney stones, although the number of case series has been increasing.^15

–18 Recently, RIRS has been a more attractive option in a growing number of centers in cases that previously would have been managed with SWL or PNL.

In this study, we presented our experience with micro-perc and RIRS in 10- to 20-mm sized renal stones in children, and reported stone-free rates and associated complications. The results of this study will guide urologists and patients/parents to decide on the treatment modality, and to select the optimal treatment. Although a recent prospective randomized controlled study compared the results of micro-perc and RIRS methods in the treatment of small kidney stones in adults,¹⁹ to the best of our knowledge, no studies have investigated the results of those methods in the pediatric population.

Materials and Methods

Patients

The study protocol was approved by the Institutional Review Board of Dicle University, Faculty of Medicine. A retrospective analysis was made of pediatric patients with renal stones that were 10 to 20 mm in size, who underwent micro-perc (n = 45) or RIRS (n = 36) in referral centers in Turkey, between August 2011 and June 2015. The preferences of patients and/or parents, and the urologist determined the treatment method, after both potential risks and benefits of the procedures had been reviewed (complication rates, stone-free rates, possible operative times, re-treatment rates, postoperative Double-J stent placement, etc.) Patients with anomalous kidneys, bleeding diatheses, musculoskeletal deformities, or a stone size >20 mm were not included. The demographic characteristics of the patients (age, stone size, and perioperative parameters) and operative outcomes were retrospectively analyzed and compared. Data were gathered from the medical databases of the hospitals.

In the preoperative period, medical history was obtained and a physical examination was performed. Complete blood count, serum biochemistry, urinalysis and urine cultures, coagulation profile, and imaging methods (plain radiograph, ultrasonography, intravenous urography, and/or computed tomography) were also obtained. A preoperative negative urine culture was required before surgery, and patients with a positive urine culture were treated in relation to the antibiogram results. The size of the stone was defined as the maximum diameter of the stone. In case of multiple calculi, the stone size was estimated as the sum of the longest axis of each stone.

Methods

Micro-perc technique

All procedures were performed under general anesthesia by using the technique as previously described by the authors.¹² The stones were fragmented by using Ho: YAG laser fiber, under direct vision. The maintenance of the visualization and the removal of stone debris through the ureter were achieved by using an irrigation pump controlled by the surgeon, and drainage of the intrarenal fluid was performed by using an open-ended ureteral catheter. The stone-free status was evaluated with endoscopic and fluoroscopic images at the end of the procedure. The procedure was terminated without any need for a nephrostomy tube.

RIRS technique

All RIRS procedures were performed under general anesthesia with the patient placed in the lithotomy position. Rigid ureteroscopy was routinely performed before flexible ureteroscopy for dilation of the ureter. A 0.035/0.038-inch hydrophilic safety guidewire was inserted into the renal pelvis under fluoroscopic guidance. Thereafter, a ureteral access sheath (9.5/11.5F, 35 cm) was placed over the hydrophilic guidewire in most of the patients. In two patients, the ureteral access sheath was not used, based on the surgeon's preference. When the rigid/flexible ureteroscope or access sheath could not be advanced easily, the stent was left for ∼1 to 2 weeks before repeating the procedure (this was necessary in six patients). In selected cases, ureteral orifice dilatation was performed with balloon dilators (only in two patients). A flexible ureterorenoscope (Flex-X2, Karl Storz, Tuttlingen, Germany/Karl Storz, Flex X2, GmbH, Tuttlingen, Germany) was inserted through the ureteral access sheath. Stone fragmentation was achieved with a 200 μm holmium laser fiber until the stone fragments were deemed small enough to be passed spontaneously. In some cases, lower pole stones were relocated to a more favorable location by basketing. Double-J stents were placed in most of the patients based on the surgeon's decision, and they were removed ∼14 to 21 days after surgery, under brief anesthesia.

All patients were evaluated with plain radiography and/or ultrasonography the day after, and 1 month after surgery to determine the stone clearance status. A stone-free status, as determined on plain X-ray or ultrasonography 1 month after surgery, was accepted as treatment success in both groups. Any residual fragments were accepted as treatment failure. The preoperative hemoglobin/postoperative first-day hemoglobin ratio was determined to evaluate blood loss during the procedures.

Statistical analysis

SPSS 16.0 package program was used for data analysis. The normality of distribution was analyzed with the Kolmogorov–Smirnov and Shapiro–Wilk tests. The independent-samples t test was used for pairwise comparisons of parameters that were distributed normally, and the Mann–Whitney U-test was used for parameters that were not distributed normally. The Chi-square test was used for non-parametric parameters. A value of p < 0.05 was accepted as statistically significant.

Results

The mean age of the patients who underwent RIRS was 8.39 ± 4.72 years, and the mean age of the patients who underwent micro-perc was 5.62 ± 4.50 years (p = 0.01). The mean stone size was 13.97 ± 3.46 mm in the micro-perc group and 12.80 ± 3.03 mm in the RIRS group (p = 0.189). The demographics and stone characteristics of the patients are summarized in Table 1.

Table 1.

Demographic Data and Stone Characteristics

	Micro-perc (n = 45)	RIRS (n = 36)	p
Age (mean ± SD) (years)	5.62 ± 4.50 (1–15)	8.39 ± 4.72 (1–16)	0.010^a
Gender, male/female (n)	23/22	15/21	0.397
Radiopacity of stone (n)—Opaque/non-opaque	34/11	33/3	0.51
Stone laterality, right/left (n)	22/23	17/19	0.88
Number of stones (n)	1.24 ± 0.57 (1–3)	1.26 ± 0.56 (1–3)	0.794
Stone size (mean ± SD) (mm)	13.97 ± 3.46 (10–19)	12.80 ± 3.03 (10–19)	0.189
Stone location, n (%)
Renal pelvis	27 (60)	14 (38.9)
Lower calix	8 (17.8)	10 (27.8)
Middle calix	8 (17.8)	1 (2.8)
Upper calix	—	2 (5.5)
Multicaliceal	2 (4.4)	9 (25)

Significant at 0.05 level.

RIRS = retrograde intrarenal surgery; SD = standard deviation.

In the micro-perc group, the access was provided subcostally, under the guidance of ultrasonography (n = 8) or fluoroscopy (n = 37), with the patient in a prone position. A Double-J stent was placed in 12 patients (26.7%), and an open-ended ureteral catheter was placed in the other 33 patients (73.3%) for better drainage of the fragments and they were removed on postoperative day 1. The mean hemoglobin drop was 0.53 ± 0.87 g/dL in the micro-perc group, and none of the cases required blood transfusion. Conversion to ultra-mini-PNL was required in one patient in the micro-perc group due to bleeding, leading to impaired vision.

In the RIRS group, balloon dilatation of the ureteral orifice was required in two cases (5.5%), and ureteral access sheaths were placed in 34 patients (94.4%). Double-J stents were placed in 28 patients (77.8%) at the end of the RIRS procedure.

There was no significant difference in the mean procedure time between the groups (p = 0.214), but fluoroscopy-screening time was significantly shorter in the RIRS group (p = 0.001). The mean hospital stay was 1.55 ± 0.77 days in the RIRS group and 2.29 ± 0.92 days in the micro-perc group (p < 0.001).

The success rate was 80% (n = 36) in the micro-perc group. Treatment failure was encountered in nine patients. In the RIRS group, the success rate was 86.2% (n = 31). The main reason for residual stones was limited deflection to lower-pole infundibula in all unsuccessful cases. Stone-free rates were similar between the groups (p = 0.47).

Six patients (13.3%) in the micro-perc group suffered from complications. Medical treatment was sufficient in three patients with postoperative renal colic, in one patient with fever, and in one patient with urinary tract infection, although Double-J stent insertion was needed in one patient due to renal colic. The mean complication rate was 16.6% (6/36) in the RIRS group. One patient suffered from renal colic, two patients had postoperative fever, and two patients had urinary tract infection. One patient was treated with a Double-J stent due to intractable pain after the procedure. When the complications were re-evaluated by using the Modified Clavien System, there was no statistical difference between the groups (p = 0.675). The perioperative and operative findings of the patients are summarized in Table 2.

Table 2.

Perioperative and Postoperative Data

	Micro-perc (n = 45)	RIRS (n = 36)	p
Operation time (minutes)	57.11 ± 15.75 (25–85)	53.25 ± 15.08 (35–90)	0.214
Fluoroscopy screening time (seconds)	81.11 ± 32.01 (30–170)	45.97 ± 32.84 (1–130)	<0.001^a
Hemoglobin drop (g/dL)	0.53 ± 0.87 (2.2–2.1)	—
Hospitalization time (mean ± SD) (days)	2.29 ± 0.92 (1–4)	1.55 ± 0.77 (1–4)	<0.001^a
Preop Double-J placement, n (%)	—	6 (16.7)
Dilation of the ureteral orifice, n (%)	—	2 (5.5)
Use of ureteral access sheath, n (%)	—	34 (94.4)
Access method, n—Fluoroscopy/Ultrasound	37/8	—
Drainage type, n (%)
None	—	8 (22.2)
Open-ended ureteral catheter	33 (73.3)	—
Double-J stent	12 (26.7)	28 (77.8)
Stone-free status, n (%)
Stone free	36 (80.0)	31 (86.2)	0.47
Residual fragments (<3 mm)	3 (6.7)	2 (5.5)
Residual fragments (≥3 mm)	6 (13.3)	3 (8.3)
Mean anesthesia session, n	1.26	1.94	<0.001^a
Complication rates, n (%)	6 (13.3)	6 (16.6)	0.675
Fever (Clavien grade I)	1	2
Renal colic (Clavien grade I)	3	1
Urinary tract infection (Clavien grade II)	1	2
Renal colic necessitating Double-J stentinsertion (Clavien grade IIIb)	1	1

Significant at 0.05 level.

Discussion

The surgical treatment of pediatric kidney stone disease has been revised in recent years. Advances in optic systems and equipment have resulted in an increase in the number of minimal invasive treatment options. The high recurrence rate and re-operation probability in children necessitate the selection of a logical surgical approach, providing a maximum stone-free rate with a minimum morbidity. The alternative treatment modalities of SWL and PNL have been increasingly reported in middle-sized pediatric renal stones in recent years.^17,20
–22

The newly developed method of “micro-percutaneous nephrolithotomy” enables access to the collecting system under direct vision, and there is no need for dilatation after access. In this way, the duration of surgery shortens, there is less exposure to radiation, and complications related to tract dilation, including bleeding and perforation, are avoided.^10,11 The stone-free rate of micro-perc in pediatric patients has been reported as 83% to 90% in literature.^12
–14 In the first report on pediatric micro-perc, the procedure was performed on 19 children with a mean stone size of 14.8 ± 6.8 mm, and the stone-free rate was reported as 89.5% at 1 month after surgery.¹⁴ Recently, Dede and colleagues¹² performed micro-perc in 24 infants younger than 2 years of age with a mean stone size of 13.5 ± 3.84 mm, and they reported the success rate as 83.3% at 1 month after surgery. In that study, postoperative renal colic was reported in four patients, and fever was reported in two patients; the mean complication rate was reported as 25%.

Some studies in literature have compared micro-perc and other treatment modalities in children. Hatipoglu et al.¹³ performed a multicenter, retrospective study, and they compared micro-perc (n = 37) and SWL (n = 108) in 145 pediatric patients who were younger than 15 years of age. They found similar complication (21.6% vs. 16.7%, respectively) and stone-free (89.2% vs. 88%, respectively) rates in micro-perc and SWL. However, in that study, the mean stone size was significantly bigger in the micro-perc group, and the rate of need for an auxiliary procedure was higher in the SWL group. Another multicenter, retrospective study compared micro-perc (n = 56) and mini-PNL (n = 63) that were performed for pediatric renal stones with a size of 10 to 20 mm, and found similar success (87.3% vs. 93.6% in the postoperative first month) and complication rates (5.3% vs. 12.6%, respectively).²¹ The authors reported that the micro-perc method had a shorter hospital stay and fluoroscopy time, and it could be preferred as an alternative to mini-PNL. In the current study, the stone-free rate was 80%, and the complication rate was 13.3% in the micro-perc group, and these results were similar to those of the aforementioned studies. There were no major complications except the Double-J stent needed in one patient due to persistent renal colic (Clavien IIIb). Conversion to ultra-mini PNL was needed in one patient due to visual loss related to bleeding.

In initial pediatric RIRS procedures, the use of large instruments and the low quality of optic technology, as well as the possibilities of ureteral ischemia, injury, stricture, and vesicoureteral reflux resulted in a delay of RIRS use in the pediatric population.²³ However, the development of more durable and thinner ureteroscopes and auxillary equipment, developments in optic systems, the introduction of intracorporeal lithotripters, and increased surgical experience have increased success and lowered complication rates.^15,17 However, most studies that have reported flexible ureteroscopy in pediatric patients have included ureteral stones and adolescents. A study performed on 100 pediatric patients with a mean age of 13.2 ± 5.4 years reported the results of 115 RIRS procedures, and it determined a stone-free rate of 91% and a total complication rate of 5.2%.²² However, only 33% of the patients had kidney stones (renal pelvis 6%, upper pole 10%, and lower pole 17%), and the success rate was not given separately for each localization. In a large series, the results of 170 flexible ureteroscopy procedures on 167 patients were presented, and it was reported that the success rate after one session was 100% in 10 mm or smaller stones, and 97% in stones bigger than 10 mm.²⁴ In that study, the stone was localized in the kidney in 60%, in the upper ureter in 28%, and in the lower ureter in 12% of the patients. The RIRS results of 21 pediatric patients with lower-pole stones were retrospectively analyzed, and the stone-free rate was reported as 76% after a follow-up period of 11 months.²⁵ That study was presented as a pediatric study, although the mean age of the participants was 15 years (range 1–20 years), and 67% of the patients were postpubertal. A multicenter study compared mini-PNL (n = 106) and RIRS (n = 95) in 201 children with kidney stones whose size ranged from 10 to 30 mm, and reported the stone-free rate as 85.8% for mini-PNL and 84.2% for RIRS after one session.¹⁷ The complication rate of RIRS was reported as 8.4% without any major complications. However, the mean age was 9.3 ± 5.2 years in the RIRS group. In the current study, the stone-free rate was found to be 86.2%, and the complication rate was found to be 16.6% in the RIRS group; these rates were in accordance with the literature. In addition, the mean age was 8.39 ± 4.72 years in the current study RIRS group, which was younger than that of the aforementioned study.

The first RIRS series that was performed in children younger than 7 years of age reported 17 RIRS procedures performed on 16 patients with a mean stone size of 11.5 mm (8–17 mm), and the success rate was 88% after one session.¹⁸ Recently, RIRS was performed in 72 kidney stones of 65 patients with a mean age of 4.31 ± 1.99 years (range, 6 months–7 years), and the stone-free and complication rates were reported as 93% and 27%, respectively.¹⁵ The authors concluded that RIRS was a safe and effective treatment modality in pre-school aged children.

The RIRS procedure in children is similar to the RIRS procedure in adults. Various studies have reported different passive dilatation, active ureteral dilatation, and ureteral access sheath use rates in RIRS procedures.^{15,16,18,22,25,26} However, most of the studies did not report the association of complications with the use of ureteral access sheath or ureteral dilatation. Ureteral orifice dilatation has been debated in children, because many authors believe that maneuvers such as hydro-distention are equivalent to active dilatation in children, and active dilatation should be performed only in selected patients.³ In the current study, balloon dilatation was applied to 2 (5.5%) patients and no complications developed. In addition, a Double-J stent was applied to 16.7% of the patients in the preoperative period for passive dilatation. The use of the ureteral access sheath has also been debated in children, particularly in those younger than 7 years of age. Although some authors have reported that it might be used at any age,¹⁵ we believe that it may have some drawbacks, including urethral injury particularly in young boys, and the surgeon should decide on its use. In the current study, the ureteral access sheath was used in 94.4% of the patients. The significantly higher mean age of the patients in the RIRS group in the current study compared with that in the micro-perc group may be due to the drawbacks related to the use of ureteral access sheaths (8.39 ± 4.72 years vs. 5.62 ± 4.50 years, p < 0.01).

Current reports state the ureteral stricture rate as 0% to 1.7%, ureteral perforation–extravasation rate as 0% to 5.6%, and vesicoureteral reflux rate as 0% to 8% after RIRS.^22,27 In the current series, only one patient had Double-J stent insertion due to persistent renal colic (Clavien grade IIIb), and there were no major complications. Vesicoureteral reflux or ureteral stricture rates could not be provided in this study, as there was no long-term follow up. Many urologists use Double-J stents routinely after RIRS.^16,18,26,28 The use of Double-J stents has been questioned since they increase postoperative morbidity, and there is a need for anesthesia for their removal, particularly in children. Double-J stents were used in 77.8% of the current study of RIRS patients. In the micro-perc group, postoperative Double-J stents were used in 12 (26.7%) patients, although the open-ended ureteral catheters were removed on postoperative day 1 in the other 33 (73.3%) patients to ensure drainage.

Micro-perc and RIRS methods were compared in a randomized prospective study for treatment of stones smaller than 1.5 cm in adults, and the authors reported similar stone-free (97.1% vs. 94.1%, p = 1.0) and complication rates.¹⁹ Hospital stay was also similar in both groups, although the decrease in hemoglobin, postoperative pain, and the need for analgesics were higher in the micro-perc group, and the need for the Double-J stent was higher in the RIRS group. Similar stone-free and complication rates were determined in the current study RIRS and micro-perc groups. When compared with the aforementioned study, the relatively lower success rate in the current study may be related to larger stone size and the inclusion of pediatric patients. Hospital stay was significantly longer in the micro-perc group. In addition, although ∼35 seconds of difference is not a long time for this type of complicated surgery, the fluoroscopy time was significantly longer in the RIRS group. As endourologists, we should keep in mind the ALARA (As Low As Reasonably Achievable) principle to avoid the harmful effects of radiation.

The following could be considered the limitations of the current study: the multicenter and retrospective nature of our study, the lack of long-term follow up, unknown stone composition, and no analysis of cost-effectiveness. That the surgical procedures were performed by different surgeons and the evaluation of stone-free status with only plain radiography and ultrasound are other limitations. Finally, the most important limitations of the present study are the criteria for the selection of the treatment modality; the RIRS method was preferred for upper pole and anterior calyx stones and in muticaliceal stones, and the micro-perc method was preferred for younger children.

Conclusion

The results of this study suggested that micro-perc and RIRS are highly effective methods for the treatment of moderately sized renal stones in children with comparable success and complication rates. Hospital stay, radiation exposure, and blood loss of micro-perc are significantly lower than in the RIRS technique. Although RIRS is effective, a major drawback is the greater requirement for Double-J stent insertion, and the consequent need for a second procedure for removal. Patients and their parents should be informed about the currently available treatment options, and of their efficacy and safety. However, further clinical trials are needed to support these results.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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