Outcomes of Ureteroscopy vs Mini-Percutaneous Nephrolithotomy for Pediatric Upper Urinary Tract Calculi: Comparative Nonrandomized Outcomes from Two Tertiary Endourology Referral Centers

Abstract

Introduction:

Pediatric upper urinary tract calculi can be treated by ureteroscopy (URS) or mini-percutaneous nephrolithotomy (mPCNL). We wanted to compare outcomes of URS and mPCNL from two tertiary referral centers that specialized in one of these treatments for pediatric stone disease.

Materials and Methods:

Data were collected from two tertiary centers for a 10-year period (2010–2019); one center specializing in URS and the other in mPCNL for consecutive patients ≤16 years undergoing either of these minimally invasive interventions. Upper urinary tract stones included stones in the kidney, pelviureteral junction, and proximal ureter, whereas mid or distal ureteral stones were excluded. Data were collected on patient and stone demographics. Outcomes of interest included stone-free rate (SFR) and complication rates.

Results:

During the study period, 55 patients underwent URS (group 1) and 40 patients underwent mPCNL (group 2). The mean stone size for groups 1 and 2 were 11.4 and 14.5 mm, respectively, whereas twice as many patients in group 1 had multiple stones. The final SFR and complication rates for groups 1 and 2 were 100% and 97.5%, and 5.4% and 12.5%, respectively. Although there were two Clavien II and one Clavien IV complication in the URS group, all five complications in mPCNL group were Clavien I.

Conclusions:

Our study shows excellent outcomes for upper urinary tract stones with both URS and mPCNL. Although treatment choices should be tailored to patients, each modality carries different advantages and our results reflect that high-volume centers specializing in a particular technique offer best outcomes, and this must also be borne in mind when counseling patients.

Introduction

The overall burden of urinary stone disease in the pediatric population is low; however, the incidence is rising.^1,2 This trend has also been mirrored in the growth and development of minimally invasive surgical methods to effectively and safely manage these patients. Pietropaolo et al. examined worldwide trends in pediatric endourologic interventions for pediatric urinary stone disease and found the highest relative increase was for percutaneous nephrolithotomy (PCNL), especially for minimally invasive PCNL techniques.³ This is largely because of the miniaturization process, which has allowed improvements to the safety profile, for example, reduced bleeding while maintaining high stone-free rates (SFRs).⁴ As a result of this, PCNL is reshaping the possibilities for the management of pediatric urinary stone disease. Similarly, since it was first described in the pediatric setting by Ritchey et al. in 1988, advancements in fiber-optic systems, laser technology, and surgeon experience have also supported the expanded role of ureteroscopy (URS) in the pediatric setting.^5,6

Our aim was to report real-world outcomes on and compare URS and mini-PCNL (mPCNL) performed in two tertiary referral centers that specialized in one of these treatments for pediatric stone disease. Our hypothesis is that both these treatment options will deliver high SFRs and offer advantages unique to the technique itself.

Materials and Methods

We collected data for a 10-year period from January 2010 to December 2019 from two tertiary endourology centers specializing in pediatric stone treatment. Center one specialized in pediatric URS technique (group 1), whereas center two specialized in pediatric mPCNL technique (group 2). The audits were registered in the respective hospitals and data were analyzed retrospectively for consecutive patients ≤16 years undergoing either of these minimally invasive interventions on an elective basis.

Upper urinary tract stones included stones in the kidney, pelviureteral junction (PUJ), and proximal ureter, whereas mid or distal ureteral stones were excluded. Data were collected on patient and stone demographics. Outcomes of interest included SFR and complication rates. Information was also collected on patient and stone demographics as well as perioperative details such as use of access sheath, ureteral stent, or nephrostomy. All patients routinely had urine culture and if positive this was treated before the intervention. Early complications (<30 days postsurgery) were graded according to the Clavien–Dindo classification.⁷

URS was performed using twin surgeon model and technique described previously.⁸ These were all done under general anesthetic (GA) and Storz FlexX2 ureteroscopes were used for the procedure. Stones were treated with Holmium YAG laser (Versa Pulse Holmium Powersuite 100 or 20 W Lumenis (UK) Ltd., Elstree, United Kingdom) using a 272-μm laser fiber (Lumenis, Inc.) and/or basket extraction, with frequency of 10 to 50 Hz and power of 0.4 to 0.8 J. An access sheath (9.5F/11.5F Cook Flexor sheath) was employed in certain cases to improve drainage, fragment collection, and to facilitate reduction of intrarenal pressure in cases of longer duration. mPCNL was performed using Storz mini ureteroscope (15F and 16F sheaths). Fragmentation was done by Holmium 100 W laser and 550-μm fiber with frequency of 20 to 40 Hz and power of 1 to 2 J. The total output varied and ranged between 30 and 70 W.

In both centers, SFR was determined at the end of the procedure through endoscopy and with ultrasound and/or plain kidney, ureter, and bladder radiograph during follow-up at 6 to 12 weeks. SFR was defined as fragments <2 mm in size.⁹ In selected URS cases, an overnight open-ended ureteral catheter was inserted at the end of the procedure or a 4.7F ureteral stent, which was then removed 4 to 8 weeks later. In most mPCNL cases only open-ended ureteral catheter was left at the end of the procedure, and this was removed before discharge from the hospital. In selected mPCNL cases ureteral stent was inserted, which was removed 3 to 4 weeks later.

Results

During the study period, 55 patients underwent URS (group 1) and 40 patients underwent mPCNL (group 2) (Table 1).

Table 1.

Outcomes of Ureteroscopy and Mini-Percutaneous Nephrolithotomy for Pediatric Upper Urinary Tract Stones

	Ureteroscopy	Mini-percutaneous nephrolithotomy
Demographics
Total no. of patients	55	40
Male:female ratio	1.1:1	1.7:1
Mean age (years)	9.2 (2–16)	8.8 (5.5–14)
Stone attributes
Mean cumulative stone size (range), mm	11.4 (range: 5–46)	14.5 (range: 8–22)
Multiple stones	29% (n = 16)	12.5% (n = 5)
Stone location
Upper pole	11%	4.5%
Interpolar	16%	2.5%
Lower pole	39%	32.5%
Renal pelvis	27%	42.5%
Upper ureter	7%	27.5%
Operative details
Postoperative stent	44% (n = 24)	30% (n = 12)
Nephrostomy	n/a	0%
Access sheath use	27% (n = 15)	n/a
Results
Initial SFR	85%	97.5%
Final SFR	100%	97.5%
Length of stay
≤24 hours	53%	92.8%
24–48 hours	47%	5.4%
>48 hours	—	1.8%
Complication rate
Overall	3 (5.4%)	5 (12.5%)
Hematuria (Clavien I)	0	3
Postoperative fever (Clavien I)	0	2
Urinary tract infection (Clavien II)	2	0
Urosepsis (Clavien IV)	1	0

SFR = stone-free rate.

Ureteroscopy

Fifty-five patients with a mean age of 9.3 (range: 2–16) years and a male:female ratio of 1.1:1 underwent URS during the study period. The mean cumulative stone size was 11.4 (range: 5–46) mm with 16 patients (29%) having multiple stones and 39% having lower pole stones. An access sheath was used in 15 patients (27%), whereas a postoperative stent was inserted in 24 patients (44%). The hospital stay was between 1 and 2 days with the initial and final SFR was 85% and 100%, respectively. Forty-seven patients had one procedure, whereas 7 had two procedures and 1 had three procedures to achieve complete stone clearance. Two of these cases were not effective initially because the ureter was too tight to access and, therefore, a ureteral stent was placed, and formal URS carried out at later date. There were three complications (5.4%) with two cases of urinary tract infection treated with oral antibiotics (Clavien II) and one case of urosepsis that needed a brief intensive care unit admission (Clavien IV).

Mini-PCNL

Forty patients with a mean age of 8.8 (range: 5.5–14) years and a male:female ratio of 1.7:1 underwent mPCNL during the study period. The mean cumulative stone size was 14.5 (range: 8–22) mm with five patients (12.5%) having multiple stones and 32.5% having lower pole stones. The renal access site was upper pole, interpolar, and lower pole in 37.5%, 32.5% and 30%, respectively. Thirty-two patients (80%) had a 15F sheath, whereas the remaining 8 patients (20%) had a 16.5F sheath inserted. Thirty-nine patients (97.5%) were stone free after one procedure. A postoperative ureteral stent was inserted in 12 patients (30%), whereas none of the patients had a percutaneous nephrostomy inserted, and 32 patients (70%) were performed as a totally tubeless procedure. The mean hospital stay was 2.2 (range: 1–3) days. There were five Clavien I complications (12.5%) with three cases of self-limiting hematuria and two cases of postoperative fever. The average hemoglobin drop was 0.23 (range: 0–1.4) g/dL with no other major or minor complications noted.

Discussion

Key findings

Our study has highlighted a high SFR that can be achieved by both URS and mPCNL (Table 1). mPCNL group had a higher SFR after a single stone treatment, whereas URS needed an average of 1.1 procedure/patient to match the SFR. Although URS was challenged by larger stones and access issues caused by tight ureter, it benefitted from lower complication rate. None of the patients in mPCNL group needed blood transfusion or nephrostomy with 70% performed as a totally tubeless procedure.

Choice of URS vs mPCNL

With exception of a few scenarios such as distal ureteral stone and large renal stones, the European association of urology (EAU)/European society paediatric urology (ESPU) guidelines put forward extracorporeal shockwave lithotripsy (SWL) as the first-line treatment of choice for pediatric urinary stone disease.¹⁰ As part of the development of URS and its delivery, there is evidence to support that it can now be carried out safely and effectively in both a medium- and high-volume setting.¹¹ Reduced length of hospital stays has allowed for cost savings related to URS. Moreover, in the adult setting, it is now predominantly carried out as day case procedure in the United Kingdom.¹² In the pediatric setting, a further advantage, which is of particular importance, is the reduced radiation exposure associated with URS compared with mPCNL related to the use of fluoroscopy during the procedure.¹³ Although SWL is the most minimally invasive procedure and carries shortest procedure time, in a recent meta-analysis by He et al. they concluded the clearance rate is lowest when compared with URS and PCNL and the overall re-treatment rate is, therefore, greatest too.¹⁴ Shouman et al. in their study set in a tertiary center reported that >80% of children underwent re-treatment after SWL.¹⁵ The standard practice for pediatric SWL still requires GA and, therefore, this advantage is lost when compared with SWL use in the adult population.

Reducing the size of the tract size has allowed PCNL to ameliorate its complication profile while maintaining its high stone clearance rate, where possible, in a single session. Previous clinical studies in pediatric setting have confirmed the correlation between increased tract size and likelihood of developing hematuria and renal extravasation.¹⁶ The choice of tract size extends beyond mPCNL only and includes ultra-mPCNL (<15) and micro-PCNL (4.85F). Silay reported the first study of this latter technique in an exclusively pediatric population with 19 children and an average age 7.5 years.¹⁷ The average stone size was 14.8 mm and 89.5% were determined stone free after 1 month. If needed, the tract size could be up-sized and converted to a larger one. There is a clear advantage in reducing the total number of treatments especially for emotional well-being of the child and mPCNL offers this. URS can be limited by a tight ureter that necessitates stent placement and repeat procedure at a later date. This occurred on two separate occasions in our study.

Strengths and limitations

This study does not provide randomized outcome data nor are the cohorts matched for comparison. However, it provides real-world insight. To date, there only exists one randomized controlled trial comparing PCNL and URS in the pediatric setting.¹⁸ This was an important study for the development of pediatric endourology; however, the total sample size was <40 and it reported on use of standard PCNL only. Therefore, any evidence, particularly if it offers more results on mPCNL, is beneficial and adds to the available body of literature in a positive way. In addition, no outcomes related to operative times, cost, or quality of life were recorded. Our study also lacked data on fluoroscopy, which is of particular importance in children. Conversely, we present a large cohort of consecutive patients from two tertiary referral centers specialized in either URS or mPCNL demonstrating good outcomes can be achieved irrespective of the chosen method.

Future research

The evolution of minimally invasive endourologic treatments signaled the end of open surgery for pediatric urinary tract stones.¹⁹ This march forward continues, and one novel technique being used now is the hybrid method of laser pop-dusting using next-generation holmium laser for hard stones, which is likely to be adopted more widely in the future.^20,21 This method can facilitate fragment retrieval, reduce use of access sheath, and reduce complications related to basket retrieval. This laser fragmentation method can also be extended for its use in mPCNL. Future randomized studies in a multicenter setting will help define further the roles and comparisons of these treatments. It would, however, need to avoid the bias of case selection, performance of the procedure, and evaluation of the parameters.

Conclusion

Our study shows excellent outcomes for upper urinary tract stones with both URS and mPCNL. Although treatment choices should be tailored to patients, each modality carries different advantages and our results reflect that high-volume centers specializing in a particular technique offer best outcomes. This should be borne in mind when counseling patients. These results also highlight that future guidelines should reflect the expanded roles and improved outcomes of these techniques.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Abbreviations Used

References

Novak

, Lakshmanan

, Trock

, et al. Sex prevalence of pediatric kidney stone disease in the United States: An epidemiological investigation. Urology, 2009; 74:104–107

Sharma

, Filler

. Epidemiology of pediatric urolithiasis. Indian J Urol, 2010; 26:516–522

Pietropaolo

, Proietti

, Jones

, et al. Trends of intervention for paediatric stone disease over the last two decades (2000–2015): A systematic review of literature. Arab J Urol, 2017; 15:306–311.

Silay

. Update on urinary stones in children: Current and future concepts in surgical treatment and shockwave lithotripsy. Eur Urol Focus, 2017; 3:164–171.

Ritchey

, Patterson

, Kelalis

. A case of pediatric ureteroscopic lasertripsy. J Urol, 1988; 139:1272–1274.

Keller

, De Coninck

, Traxer

. Next-generation fiberoptic and digital ureteroscopes. Urol Clin, 2019; 46:147–163.

Mitropoulos

, Artibani

, Biyani

. Validation of the Clavien–Dindo grading system in urology by the European association of urology guidelines ad hoc panel. Eur Urol Focus, 2018; 4:608–613.

Somani

, Griffin

. Ureteroscopy for paediatric calculi: The twin-surgeon model. J Pediatr Urol, 2018; 14:73–74.

Somani

, Desai

, Traxer

, et al. Stone free rate (SFR): A new proposal for defining levels of SFR. Urolithiasis, 2014; 42:95

10.

Radmayr

, Bogaert

, Dogan

, et al. EAU guidelines on paediatric Urology. In:EAU Guidelines, edition presented at the Annual EAU Congress Barcelona. 2019.

11.

Rob

, Jones

, Pietropaolo

, et al. Ureteroscopy for stone disease in paediatric population is safe and effective in medium-volume and high-volume centres: Evidence from a systematic review. Curr Urol Rep, 2017; 18:92.

12.

Ghosh

, Oliver

, Way

, et al. Results of day-case ureterorenoscopy (DC-URS) for stone disease: Prospective outcomes over 4.5 years. World J Urol, 2017; 35:1757–1764.

13.

Kirac

, Ergin

, Kibar

, et al. The efficacy of ureteroscopy without fluoroscopy for ureteral and renal stones in pediatric patients. J Endourol, 2018; 32:100–105.

14.

, Xiao

, Chen

, et al. Which is the best treatment of pediatric upper urinary tract stones among extracorporeal shockwave lithotripsy, percutaneous nephrolithotomy and retrograde intrarenal surgery: A systematic review. BMC Urol, 2019; 19:98.

15.

Shouman

, Ziada

, Ghoneim

, et al. Extracorporeal shock wave lithotripsy monotherapy for renal stones >25 mm in children. Urology, 2009; 74:109–111

16.

Jones

, Bennett

, Aboumarzouk

, et al. Role of minimally invasive percutaneous nephrolithotomy techniques—micro and ultra-mini PCNL (%3c 15F) in the pediatric population: A systematic review. J Endourol, 2019; 31:816–824.

17.

Silay

. Initial report of microperc in the treatment of pediatric nephrolithiasis. J Pediatr Surg, 2013; 48:1578–1583.

18.

Saad

, Youssif

, Al Islam Nafis Hamdy

, et al. Percutaneous nephrolithotomy vs retrograde intrarenal surgery for large renal stones in pediatric patients: A randomized controlled trial. J Urol, 2015; 194:1716–1720.

19.

Hiler

, Ghani

. Frontiers of stone management. Curr Opin Urol, 2020; 30:17–23.

20.

Pietropaolo

, Jones

, Whitehurst

, Somani

. Role of ‘dusting and pop-dusting’ using a high-powered (100 W) laser machine in the treatment of large stones (≥ 15 mm): Prospective outcomes over 16 months. Urolithiasis, 2019; 47:391–394.

21.

Reeves

, Griffin

, Pietropaolo

, Somani

. Feasibility of dusting and pop-dusting using high-power (100W) Holmium YAG (Ho: YAG) laser in treatment of paediatric stones: Results of first worldwide clinical study. Cent Eur J Urol, 2019; 72:398–401.