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Role of Pediatric Ureteral Access Sheath and Outcomes Related to Flexible Ureteroscopy and Laser Stone Fragmentation: A Systematic Review of Literature

Open AccessPublished:October 12, 2022DOI:https://doi.org/10.1016/j.euros.2022.09.012

      Abstract

      Context

      Flexible ureteroscopy and laser lithotripsy (FURSL) represent a good treatment option for pediatric urolithiasis. Scarce evidence is available about the safety and efficacy of the concomitant use of a ureteral access sheath (UAS) in the setting of pediatric ureteroscopy (URS).

      Objective

      To acquire all the available evidence on UAS usage in pediatric FURSL, focusing on intra- and postoperative complications and stone-free rates (SFRs).

      Evidence acquisition

      We performed a systematic literature research using PubMed/MEDLINE, Embase, and Scopus databases. The inclusion criteria were cohorts of pediatric patients <18 yr old, submitted to URS for FURSL, reporting on more than ten cases of UAS placement. The primary outcomes were prestenting rates, operating time, ureteric stent placement rates after surgery, rates and grades of complications, ureteral injuries, and overall SFR. A total of 22 articles were selected.

      Evidence synthesis

      In total, 26 intraoperative and 130 postoperative complications following URS with UAS placement were reported (1.8% and 9.18% of the overall procedures, respectively). According to the Clavien-Dindo classification, 32 were classified as Clavien I, 29 as Clavien II, 43 as Clavien I or II, six as Clavien III, and one as Clavien IV. Twenty-one cases of ureteral injuries (1.59%) were noted in the whole cohort; most of them were ureteral perforation or extravasation, and were treated with a temporary indwelling ureteric stent. The overall SFR after a single URS procedure was 76.92%; after at least a second procedure, it was 84.9%.

      Conclusions

      FURSL is a safe and effective treatment option for pediatric urolithiasis. UAS use was associated with a low rate of ureteric injuries, mostly treated and resolved with a temporary indwelling ureteric stent.

      Patient summary

      We performed a systematic literature research on the utilization of a UAS during ureteroscopy for stone treatment in pediatric patients. We assessed the outcomes related to the rates of intra- and postoperative complications and the rates of efficacy of the procedure in the clearance of stones. The evidence shows a low rate and grade of complications associated with UAS placement and good stone-free outcomes. A ureteric injury may occur in 1.6% of cases, but it is usually managed and resolved with a temporary indwelling ureteric stent.

      Keywords

      1. Introduction

      Pediatric urolithiasis is an emerging issue among urological practice. Its incidence has risen over the past decades in Europe and North America [
      • Dwyer M.E.
      • Krambeck A.E.
      • Bergstralh E.J.
      • Milliner D.S.
      • Lieske J.C.
      • Rule A.D.
      Temporal trends in incidence of kidney stones among children: a 25-year population based study.
      ,
      • Van Batavia J.P.
      • Tasian G.E.
      Clinical effectiveness in the diagnosis and acute management of pediatric nephrolithiasis.
      ,
      • Routh J.C.
      • Graham D.A.
      • Nelson C.P.
      Epidemiological trends in pediatric urolithiasis at United States freestanding pediatric hospitals.
      ,
      • Tasian G.E.
      • Ross M.E.
      • Song L.
      • et al.
      Annual incidence of nephrolithiasis among children and adults in South Carolina from 1997 to 2012.
      ], and consequently, its overall economic burden on both the emergency department and inpatient admissions [
      • Wang H.-H.S.
      • Wiener J.S.
      • Lipkin M.E.
      • Scales C.D.
      • Ross S.S.
      • Routh J.C.
      Estimating the nationwide, hospital based economic impact of pediatric urolithiasis.
      ]. Metabolic abnormalities that increase the risk of nephrolithiasis, especially hypercalciuria and hypocitraturia, can be identified in 75–84% of pediatric patients [
      • Tasian G.E.
      • Copelovitch L.
      Evaluation and medical management of kidney stones in children.
      ]. Anatomic or structural defects, such as pelvic-ureteric junction obstruction, are the most common predisposition to pediatric urolithiasis. Despite this, most patients with these abnormalities will not face stone formation, suggesting a more complex and multifactorial process involving genetic, dietary, and environmental factors [
      • Bowen D.K.
      • Tasian G.E.
      Pediatric stone disease.
      ].
      As regards treatment, according to European Association of Urology (EAU) guidelines, shockwave lithotripsy (SWL) still represents the first choice for most pediatric renal stones, while percutaneous nephrolithotomy (PCNL) should be reserved for larger and complex stones [

      Radmayr C, Bogaert G, Dogan HS, et al. EAU guidelines. Presented at the EAU Annual Congress Milan 2021. 2021.

      ]. However, the uptake of ureteroscopy (URS) as a safe and highly effective option in the pediatric population has markedly increased due to advancements related to optic systems, miniaturized equipment, and surgeon expertise [
      • Ishii H.
      • Griffin S.
      • Somani B.K.
      Ureteroscopy for stone disease in the paediatric population: a systematic review.
      ]. Nowadays, flexible URS and laser lithotripsy (FURSL) in the management of pediatric renal stones allows surgeons to deal with stones safely and effectively even in lower pole location and in children from the age of 3 mo [
      • Ishii H.
      • Griffin S.
      • Somani B.K.
      Flexible ureteroscopy and lasertripsy (FURSL) for paediatric renal calculi: results from a systematic review.
      ].
      The use of a ureteral access sheath (UAS) during FURSL in the adult population is well established. The most relevant advantages in using a UAS are repeated entrance into the ureter and collecting system, lower intrapelvic pressure, as well as protection to both the ureteroscope and the ureter when extracting stone fragments [
      • De Coninck V.
      • Keller E.X.
      • Rodríguez-Monsalve M.
      • Audouin M.
      • Doizi S.
      • Traxer O.
      Systematic review of ureteral access sheaths: facts and myths.
      ]. Moreover, a UAS allows better visibility and decreased risks of postoperative sepsis and bleeding. However, little evidence is available regarding the utilization of a UAS in the setting of pediatric URS, and concerns have been raised on the risks of ureteral injuries, tissue ischemia related to overdilation, and risk of ureteric stricture.
      The aim of this systematic review was to acquire all the available and most up-to-date evidence on UAS placement in pediatric FURSL, focusing on its outcomes such as peri- and postoperative complications and overall stone-free rate (SFR).

      2. Evidence acquisition

      We searched PubMed/MEDLINE, Embase, and Scopus databases following the Preferred Reporting of Systematic Reviews and Meta-analyses (PRISMA) guidelines [
      • Shamseer L.
      • Moher D.
      • Clarke M.
      • et al.
      Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015: elaboration and explanation.
      ]. Search terms included the following: “paediatric/pediatric kidney stones,” ”paediatric/pediatric stones,“ ”paediatric/pediatric urolithiasis,“ ”ureteral access sheath,“ ”UAS,“ ”ureteric access sheath,“ “URS,” “retrograde intrarenal surgery,” “RIRS,” and ”ureteroscopy.“ The references of identified studies were examined to find any further potential studies for inclusion. Boolean operators (AND, OR) were employed. The research was limited to English-language articles without any restriction on the publishing year.
      The inclusion criteria were as follows:
      • 1.
        Cohorts of pediatric patients <18 yr old
      • 2.
        Submitted to URS for FURSL
      • 3.
        Studies reporting on more than ten cases of UAS placement
      Patient characteristics, and intra- and postoperative variables were described. The primary outcomes were prestenting rates, operating time, ureteric stent placement after surgery, rates and grades of complications, ureteral injuries, and overall SFR. No randomized controlled trial (RCT) compared pediatric URS with versus without UAS placement. As the outcome measures and reporting were not standardized, a formal meta-analysis could not be performed.

      3. Evidence synthesis

      The literature search provided 468 results. After removing duplicates, a total of 202 abstracts were considered for eligibility. Review articles and conference abstracts were excluded from the analysis. Eventually, 48 full-text articles were assessed. Among these, five articles did not meet the inclusion criteria, eight were excluded because a UAS was not used during URS, seven did not specify the rate of UAS placement in the cohort of procedures, and six had a case series with fewer than ten patients. In the end, we selected 22 articles for our analysis (Table 1 and Fig. 1). All manuscripts were published between 2007 and 2022.
      Table 1Descriptive characteristics of the studies included in the analysis
      AuthorYearPatients (n)Procedures (n)Age, mean (range)Age limit (yr)Gender, n (%)Stone size (mm), mean (range)Operating time (min), mean (range)Prestenting, n (%)
      Quiroz Madarriaga
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      20228229.5 (4–18)18M 7 (87.5); F 1 (12.5)7.7 (5–18)120 (100–300)5 (62.5)
      Lim
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      20223143149.54 (0.42–16)18M 185 (58.9); F 128 (41.1)10.7 (8–12)60 (45–90)155 (49.4)
      Ferretti
      • Ferretti S.
      • Cuschera M.
      • Campobasso D.
      • et al.
      Rigid and flexible ureteroscopy (URS/RIRS) management of paediatric urolithiasis in a not endemic country.
      202128408 (2–16)16M 19 (67.8); F 9 (32.2)9.5 (5–24)77.7 (20–140)17 (56.6)
      Kahraman
      • Kahraman O.
      • Dogan H.S.
      • Asci A.
      • Asi T.
      • Haberal H.B.
      • Tekgul S.
      Factors associated with the stone-free status after retrograde intrarenal surgery in children.
      202146465.87 (0.5–17.8)17M 29 (63); F 17 (37)8.5 (3–20)60 (45–120)21 (45.6)
      Chandramohan
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      202162673.51 (0.3–5)5M 40 (64.5); F 22 (35.5)11.9 (7.3–18.2)55.2 (36.4–80.5)62 (100)
      Mosquera
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      2021484810.72 (1.1–16.9)16M 24 (50); F 24 (50)10.41 (3–20)NA20 (41.7)
      Ozkent
      • Ozkent M.S.
      • Piskin M.M.
      • Balasar M.
      • Goger Y.E.
      • Sonmez M.G.
      Is retrograde intrarenal surgery as safe for children as it is for adults?.
      202155557.2 (0.6–17)17M 28 (50.9); F 27 (49.1)13.9 (7.3–20.5)61.8 (39.5–84.1)29 (52.7)
      Aljumaiah
      • Aljumaiah S.
      • Allubly N.
      • Alshammari A.
      • Alkhamees M.
      • Bin H.S.
      Small ureteral access sheath in treating paediatric urolithiasis: a single centre experience.
      202014159.5 (9–17)17M 9 (64.3); F 5 (35.7)12.5 (10–20)55.7 (24–120)NA
      Jones
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      2020811028.8 (1.5–16)16M 39 (47); F 43 (53)11.5 (4–46)NA35 (34.7)
      Jones
      • Jones P.
      • Mishra D.
      • Agrawal M.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy vs mini-percutaneous nephrolithotomy for pediatric upper urinary tract calculi: comparative nonrandomized outcomes from two tertiary endourology referral centers.
      202055559.3 (2–16)16M 26 (47); F 29 (53)11.4 (5–46)NANA
      Sforza
      • Sforza S.
      • Tuccio A.
      • Grosso A.A.
      • Crisci A.
      • Cini C.
      • Masieri L.
      Could surgical experience of adult endourologist overcome the learning curve of retrograde intrarenal surgery in children?.
      2020151511.8 (8–16)NAM 8 (53.3); F 7 (46.7)9.48 (8.9–12)70 (60–80)8 (53.3)
      Anbarasan
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      2019212111.8 (2–16)16M 10 (48); F 11 (52)15.4 (5–30)NA8 (38)
      Berrettini
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      201813163.91 (0.75–6.5)6M 5 (38); F 8 (62)15.5 (9–23)98.2 (16–75)16 (100)
      Yuruk
      • Yuruk E.
      • Tuken M.
      • Gonultas S.
      • et al.
      Retrograde intrarenal surgery in the management of pediatric cystine stones.
      2017141410.9 (7–15)NAM 8 (57.1); F 6 (42.8)13.6 (10–18)38.2 (30–50)1 (7.1)
      Featherstone
      • Featherstone N.C.
      • Somani B.K.
      • Griffin S.J.
      Ureteroscopy and laser stone fragmentation (URSL) for large (≥1 cm) paediatric stones: outcomes from a university teaching hospital.
      2017183510.4 (3.6–15)NAM 7 (39); F 11 (61)13.3 (10–25)NA1 (5.5)
      Erkurt
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      201465654.31 (0.5–7)7M 31(48); F 34 (52)14.66 (7–30)46.47 (20–95)17 (26.1)
      Wang
      • Wang H.H.
      • Huang L.
      • Routh J.C.
      • Kokorowski P.
      • Cilento B.G.
      • Nelson C.P.
      Use of the ureteral access sheath during ureteroscopy in children.
      2011969613 (1.5–20.9)NAM 34 (35); F 62 (65)9.6 (0.8–54)92 (23–218)26 (27)
      Yeow
      • Yeow W.C.
      • Pemberton R.
      • Barker A.
      Flexible ureterorenoscopy and laser lithotripsy in children.
      200926268.2 (0.25–15)NAM 14 (54); F 12 (46)10.3 (3–21)NA25 (96.1)
      Tanaka
      • Tanaka S.T.
      • Makari J.H.
      • Pope IV, J.C.
      • Adams M.C.
      • Brock J.W.
      • Thomas J.C.
      Pediatric ureteroscopic management of intrarenal calculi.
      200850527.9 (1.2–13.6)14M 31 (62); F 19 (38)8 (1–16)NA29 (56)
      Kim
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      20081671705.2 (0.25–18.1)18M 89 (53.3); F 78 (46.7)6.12 (3–24)107 (72–196)95 (57)
      Cannon
      • Cannon G.M.
      • Smaldone M.C.
      • Wu H.Y.
      • et al.
      Ureteroscopic management of lower-pole stones in a pediatric population.
      2007212715.1 (1–20)NAM 8 (38); F 13 (62)12.2 (6.3–18.1)NA8 (38)
      Smaldone
      • Smaldone M.C.
      • Cannon G.M.
      • Wu H.Y.
      • et al.
      Is ureteroscopy first line treatment for pediatric stone disease?.
      200710011513.2 (7.8–18.6)NAM 42 (42); F 58 (58)8.3 (2.7–13.9)NA54 (54)
      F = female; M = male; NA = not available.
      Figure thumbnail gr1
      Fig. 1PRISMA flowchart of the included studies. PRISMA = Preferred Reporting of Systematic Reviews and Meta-analyses; UAS = ureteral access sheath.

      3.1 Patients characteristics

      Overall, 1317 patients (693 males and 624 females) were included, and 1416 ureteroscopies with UAS placement were performed. Some patient cohorts were relatively small (eight patients with cystinuria submitted to multiple procedures [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ]); conversely, one article gathered data from eight different centers globally in a multicentric study [
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      ], collecting data from 314 pediatric patients. Two articles showed outcomes from large cohorts of patients in tertiary endourological referral centers (167 patients and 170 URS procedures [
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      ], and 81 patients and 102 URS procedures [
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      ]). The mean age of patients was 8.9 yr. Most of the included studies set 18 yr as the age limit; three studies analyzed the outcomes and feasibility of URS in preschool children (Erkurt et al. [
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ] in children aged <7 yr, Berrettini et al. [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ] in preschool children weighing <20 kg, and Chandramohan et al. [
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ] in patients <5 yr old). The pediatric population accounted for 693 males (52.6%) and 624 females (47.4%). The mean stone size was 11.1 mm across studies; it exceeded 15 mm in two studies [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ,
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      ] only. Stone size was usually defined as the largest linear diameter of a single stone or the sum of long axes in the case of multiple stones. Ferretti et al. [
      • Ferretti S.
      • Cuschera M.
      • Campobasso D.
      • et al.
      Rigid and flexible ureteroscopy (URS/RIRS) management of paediatric urolithiasis in a not endemic country.
      ] specified stone length range and stone surface area; others [
      • Aljumaiah S.
      • Allubly N.
      • Alshammari A.
      • Alkhamees M.
      • Bin H.S.
      Small ureteral access sheath in treating paediatric urolithiasis: a single centre experience.
      ] subclassified stone burden in <10, 10–20, and >20 mm. There was great heterogeneity among studies regarding diagnostic investigations, with most groups using ultrasound for kidney, ureter, and bladder or x-rays, and occasional low-dose non-contrast computed tomography.

      3.2 Prestenting rates

      We report no broad agreement on the opportunity of prestenting in the setting of pediatric URS among the selected studies. Indeed, the mean rate of prestented patients was 50%, reflecting different clinical practices in the management of pediatric URS. Two groups [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ,
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ] treating patients <5 yr old put a JJ stent in 100% of patients and one group [
      • Yeow W.C.
      • Pemberton R.
      • Barker A.
      Flexible ureterorenoscopy and laser lithotripsy in children.
      ] in 96.1% of patients. This action was performed 12 or 14 d before the procedure to obtain a passive dilatation of the ureter. On the contrary, a preoperative JJ stent was placed only in one out of 14 (7.1%) patients by Yuruk et al. [
      • Yuruk E.
      • Tuken M.
      • Gonultas S.
      • et al.
      Retrograde intrarenal surgery in the management of pediatric cystine stones.
      ] and in one out of 18 (5.5%) patients by Featherstone et al. [
      • Featherstone N.C.
      • Somani B.K.
      • Griffin S.J.
      Ureteroscopy and laser stone fragmentation (URSL) for large (≥1 cm) paediatric stones: outcomes from a university teaching hospital.
      ], due to obstruction and urosepsis before the surgical treatment.

      3.3 UAS placement rates, calibers, and lengths

      Overall, a UAS was placed in 603 procedures in the cohort of selected studies (Table 2). Anbarasan et al. [
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      ] analyzed a whole group of patients (21) who underwent FURSL with an access sheath; Mosquera et al. [
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      ] reported one of the largest UAS cohorts in pediatric patients carried out in two high-volume endourology centers, including 48 cases. Most groups used a 9.5 or 11.5 Fr UAS (three used 9.5 Fr UAS, three 11–9.5 Fr UAS, seven 11.5–9.5 UAS, and one 10–12 Fr UAS). Seven groups [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ,
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      ,
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      ,
      • Yeow W.C.
      • Pemberton R.
      • Barker A.
      Flexible ureterorenoscopy and laser lithotripsy in children.
      ,
      • Wang H.H.
      • Huang L.
      • Routh J.C.
      • Kokorowski P.
      • Cilento B.G.
      • Nelson C.P.
      Use of the ureteral access sheath during ureteroscopy in children.
      ,
      • Cannon G.M.
      • Smaldone M.C.
      • Wu H.Y.
      • et al.
      Ureteroscopic management of lower-pole stones in a pediatric population.
      ,
      • Smaldone M.C.
      • Cannon G.M.
      • Wu H.Y.
      • et al.
      Is ureteroscopy first line treatment for pediatric stone disease?.
      ] used different caliber access sheaths, depending on the surgeon’s choice, with calibers varying from 8 to 15 Fr. One study [
      • Tanaka S.T.
      • Makari J.H.
      • Pope IV, J.C.
      • Adams M.C.
      • Brock J.W.
      • Thomas J.C.
      Pediatric ureteroscopic management of intrarenal calculi.
      ] did not report UAS caliber. UAS length was specified only in nine out of 22 studies, with four groups using a 35 cm UAS [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ,
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      ,
      • Aljumaiah S.
      • Allubly N.
      • Alshammari A.
      • Alkhamees M.
      • Bin H.S.
      Small ureteral access sheath in treating paediatric urolithiasis: a single centre experience.
      ,
      • Ozkent M.S.
      • Piskin M.M.
      • Balasar M.
      • Goger Y.E.
      • Sonmez M.G.
      Is retrograde intrarenal surgery as safe for children as it is for adults?.
      ], two using either a 20 or a 28 cm UAS [
      • Ferretti S.
      • Cuschera M.
      • Campobasso D.
      • et al.
      Rigid and flexible ureteroscopy (URS/RIRS) management of paediatric urolithiasis in a not endemic country.
      ,
      • Sforza S.
      • Tuccio A.
      • Grosso A.A.
      • Crisci A.
      • Cini C.
      • Masieri L.
      Could surgical experience of adult endourologist overcome the learning curve of retrograde intrarenal surgery in children?.
      ], one using a 28 cm UAS only [
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ], one using either a 20 or a 35 cm UAS [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ], and one using either a 28 or a 35 cm UAS [
      • Yuruk E.
      • Tuken M.
      • Gonultas S.
      • et al.
      Retrograde intrarenal surgery in the management of pediatric cystine stones.
      ].
      Table 2Intra- and postoperative outcomes of stone treatment and UAS placement
      AuthorPatients (n)UAS n (%)UAS caliber (%)UAS length (cm)DJ placement, n (%)Intraoperative complications n (%)Postoperative complication rate, n (%)Clavien-Dindo grade (n)Ureteral injuries, n (%)Ureteral injuries connected to UASSFR I (%)SFR II (%)
      Quiroz Madarriaga
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      815 (68)10–12 Fr (60); 12–14 Fr (40)357 (90.9)4 (18.2)6 (27)II (5); IIIa (1)1 (0.04)NA59.00
      Lim
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      314171 (54.5)>8 Fr (78)NANA5 (0.02)43 (13.7)I–II (43)5 (1.6)NA75.40
      Ferretti
      • Ferretti S.
      • Cuschera M.
      • Campobasso D.
      • et al.
      Rigid and flexible ureteroscopy (URS/RIRS) management of paediatric urolithiasis in a not endemic country.
      2812 (50)9.5 Fr20/2837 (75.5)NA4 (10.8)I (2); II (2)NANA76.6093.30
      Kahraman
      • Kahraman O.
      • Dogan H.S.
      • Asci A.
      • Asi T.
      • Haberal H.B.
      • Tekgul S.
      Factors associated with the stone-free status after retrograde intrarenal surgery in children.
      4616 (34.8)11–9.5 FrNANANA2 (4.3)I (2)0061.00
      Chandramohan
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      6240 (63.5)11.5–9.5 Fr2867 (100)2 (3)24 (38)I (18); II (2); IIIb (4)2 (1 grade I; 1 grade II)2/2 (100%)76.30
      Mosquera
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      4848 (100)11.5–9.5 FrNA27 (56.3)NA1 (2.1)II (1)1 (2.1, grade I)1/1 (100%)66.60100.00
      Ozkent
      • Ozkent M.S.
      • Piskin M.M.
      • Balasar M.
      • Goger Y.E.
      • Sonmez M.G.
      Is retrograde intrarenal surgery as safe for children as it is for adults?.
      5519 (34.5)11–9.5 Fr3523 (41.8)1 (1.8)9 (16.3)NANANA81.80
      Aljumaiah
      • Aljumaiah S.
      • Allubly N.
      • Alshammari A.
      • Alkhamees M.
      • Bin H.S.
      Small ureteral access sheath in treating paediatric urolithiasis: a single centre experience.
      1414 (100)10–12 Fr3514 (100)00NA0078.60
      Jones
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      8121 (20.5)11.5–9.5 FrNA61 (60)03 (3)I (1); II (1); IV (1)0073.0099.00
      Jones
      • Jones P.
      • Mishra D.
      • Agrawal M.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy vs mini-percutaneous nephrolithotomy for pediatric upper urinary tract calculi: comparative nonrandomized outcomes from two tertiary endourology referral centers.
      5515 (27)11.5–9.5 FrNA24 (44)NA3 (5.4)II (2); IV (1)0085.00100.00
      Sforza
      • Sforza S.
      • Tuccio A.
      • Grosso A.A.
      • Crisci A.
      • Cini C.
      • Masieri L.
      Could surgical experience of adult endourologist overcome the learning curve of retrograde intrarenal surgery in children?.
      1515 (100)9.5 Fr20/2815 (100)NA2 (13.3)II (2)0086.70
      Anbarasan
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      2121 (100)11–9.5 Fr3514 (67)00NA0095.00
      Berrettini
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      1315 (93.8)11.5–9.5 Fr20/3516 (100)NA6 (37.5)I (3); II (2); IIIb (1)0081.30
      Yuruk
      • Yuruk E.
      • Tuken M.
      • Gonultas S.
      • et al.
      Retrograde intrarenal surgery in the management of pediatric cystine stones.
      1412 (85.7)11.5–9.5 Fr28/3512 (85.7)1 (7.1)1 (7.1)II (2)1 (7.1, grade I)1/1 (100%)100.00
      Featherstone
      • Featherstone N.C.
      • Somani B.K.
      • Griffin S.J.
      Ureteroscopy and laser stone fragmentation (URSL) for large (≥1 cm) paediatric stones: outcomes from a university teaching hospital.
      1817 (49)9.5 FrNA21 (60)00NA0033.3089.00
      Erkurt
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      6540 (61.5)11.5–9.5 FrNANANA18 (27.7)I (6); II (10); III (2)2 (3)NA87.0792.30
      Wang
      • Wang H.H.
      • Huang L.
      • Routh J.C.
      • Kokorowski P.
      • Cilento B.G.
      • Nelson C.P.
      Use of the ureteral access sheath during ureteroscopy in children.
      9640 (42)11–13 Fr (37); 12–14 Fr (52); 13–15 Fr (11)NA75 (78)7 (7.3)7 (7.3)NA46/7 (85.7%)70.00
      Yeow
      • Yeow W.C.
      • Pemberton R.
      • Barker A.
      Flexible ureterorenoscopy and laser lithotripsy in children.
      2612 (46.2)11.5–9.5 Fr/12–10 FrNANA00NA0088.50
      Tanaka
      • Tanaka S.T.
      • Makari J.H.
      • Pope IV, J.C.
      • Adams M.C.
      • Brock J.W.
      • Thomas J.C.
      Pediatric ureteroscopic management of intrarenal calculi.
      5025 (48)NANA51 (98)01 (1.9)NA0050.0058.00
      Kim
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      167NA9.5 Fr/10 FrNA72 (42.4)00NA00100.00
      Cannon
      • Cannon G.M.
      • Smaldone M.C.
      • Wu H.Y.
      • et al.
      Ureteroscopic management of lower-pole stones in a pediatric population.
      2111 (43)12 Fr/9.5 FrNA15 (71)00NA0076.00
      Smaldone
      • Smaldone M.C.
      • Cannon G.M.
      • Wu H.Y.
      • et al.
      Is ureteroscopy first line treatment for pediatric stone disease?.
      10024 (24)11–9.5 Fr (14); 14–12 Fr (10)NA76 (76)6 (5.2)NANA5NA91.00
      NA = not available; SFR I = stone-free rate after first ureteroscopy; SFR II = stone-free rate after >1 ureteroscopy; UAS = ureteral access sheath.

      3.4 Postoperative stent placement

      Eighteen articles reported data on the postoperative placement of a ureteric stent. Great heterogeneity emerged, with three groups [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ,
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ,
      • Sforza S.
      • Tuccio A.
      • Grosso A.A.
      • Crisci A.
      • Cini C.
      • Masieri L.
      Could surgical experience of adult endourologist overcome the learning curve of retrograde intrarenal surgery in children?.
      ] choosing to insert a stent in every patient (either a ureteral catheter or a JJ stent) and two groups [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ,
      • Tanaka S.T.
      • Makari J.H.
      • Pope IV, J.C.
      • Adams M.C.
      • Brock J.W.
      • Thomas J.C.
      Pediatric ureteroscopic management of intrarenal calculi.
      ] in >90% of patients, compared with three groups [
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      ,
      • Ozkent M.S.
      • Piskin M.M.
      • Balasar M.
      • Goger Y.E.
      • Sonmez M.G.
      Is retrograde intrarenal surgery as safe for children as it is for adults?.
      ,
      • Jones P.
      • Mishra D.
      • Agrawal M.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy vs mini-percutaneous nephrolithotomy for pediatric upper urinary tract calculi: comparative nonrandomized outcomes from two tertiary endourology referral centers.
      ] that put a stent in <50% of patients. Four studies [
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      ,
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ,
      • Yeow W.C.
      • Pemberton R.
      • Barker A.
      Flexible ureterorenoscopy and laser lithotripsy in children.
      ,
      • Kahraman O.
      • Dogan H.S.
      • Asci A.
      • Asi T.
      • Haberal H.B.
      • Tekgul S.
      Factors associated with the stone-free status after retrograde intrarenal surgery in children.
      ] did not report data on postoperative stent placement. Stent removal was achieved after a mean of 21.5 d, with most of the groups leaving it for 10–14 d [
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      ,
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ,
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ,
      • Ferretti S.
      • Cuschera M.
      • Campobasso D.
      • et al.
      Rigid and flexible ureteroscopy (URS/RIRS) management of paediatric urolithiasis in a not endemic country.
      ,
      • Yeow W.C.
      • Pemberton R.
      • Barker A.
      Flexible ureterorenoscopy and laser lithotripsy in children.
      ], others for 21–28 d [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ,
      • Yuruk E.
      • Tuken M.
      • Gonultas S.
      • et al.
      Retrograde intrarenal surgery in the management of pediatric cystine stones.
      ,
      • Sforza S.
      • Tuccio A.
      • Grosso A.A.
      • Crisci A.
      • Cini C.
      • Masieri L.
      Could surgical experience of adult endourologist overcome the learning curve of retrograde intrarenal surgery in children?.
      ] or up to 6–8 wk [
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      ,
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      ].

      3.5 Complication rates

      Regarding surgical complications, a total of 26 intraoperative and 130 postoperative complications were reported among the 22 selected articles, accounting for 1.8% and 9.18% of the overall procedures, respectively. Intraoperative complications included: rupture of the laser fiber during lithotripsy, intrarenal bleeding, ureteral injury [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ], pelvicalyceal system or ureteric injury [
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      ], ureteric damage [
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ], ureteral perforation with extravasation, submucosal wire, and proximal stent migration [
      • Wang H.H.
      • Huang L.
      • Routh J.C.
      • Kokorowski P.
      • Cilento B.G.
      • Nelson C.P.
      Use of the ureteral access sheath during ureteroscopy in children.
      ], and one case of distal ureteral stricture requiring ureteral reimplantation [
      • Smaldone M.C.
      • Cannon G.M.
      • Wu H.Y.
      • et al.
      Is ureteroscopy first line treatment for pediatric stone disease?.
      ]. Postoperative complications reported were the following: fever, obstructive pyelonephritis [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ], hematuria [
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ,
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ,
      • Sforza S.
      • Tuccio A.
      • Grosso A.A.
      • Crisci A.
      • Cini C.
      • Masieri L.
      Could surgical experience of adult endourologist overcome the learning curve of retrograde intrarenal surgery in children?.
      ], sepsis [
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      ,
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      ], vomiting, urinary tract infection [
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ,
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ,
      • Ferretti S.
      • Cuschera M.
      • Campobasso D.
      • et al.
      Rigid and flexible ureteroscopy (URS/RIRS) management of paediatric urolithiasis in a not endemic country.
      ,
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      ], pain, urinary retention [
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      ], hydrocalyx [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ], ureteral wall injury [
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ], postoperative hydronephrosis [
      • Wang H.H.
      • Huang L.
      • Routh J.C.
      • Kokorowski P.
      • Cilento B.G.
      • Nelson C.P.
      Use of the ureteral access sheath during ureteroscopy in children.
      ], voiding symptoms, and rehospitalization [
      • Tanaka S.T.
      • Makari J.H.
      • Pope IV, J.C.
      • Adams M.C.
      • Brock J.W.
      • Thomas J.C.
      Pediatric ureteroscopic management of intrarenal calculi.
      ]. Six studies reported no postoperative complications [
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      ,
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      ,
      • Aljumaiah S.
      • Allubly N.
      • Alshammari A.
      • Alkhamees M.
      • Bin H.S.
      Small ureteral access sheath in treating paediatric urolithiasis: a single centre experience.
      ,
      • Yeow W.C.
      • Pemberton R.
      • Barker A.
      Flexible ureterorenoscopy and laser lithotripsy in children.
      ,
      • Featherstone N.C.
      • Somani B.K.
      • Griffin S.J.
      Ureteroscopy and laser stone fragmentation (URSL) for large (≥1 cm) paediatric stones: outcomes from a university teaching hospital.
      ,
      • Cannon G.M.
      • Smaldone M.C.
      • Wu H.Y.
      • et al.
      Ureteroscopic management of lower-pole stones in a pediatric population.
      ].

      3.6 Complication types

      Twelve articles reported surgical complications according to the Clavien-Dindo classification [
      • Dindo D.
      • Demartines N.
      • Clavien P.-A.
      Classification of surgical complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey.
      ]. Thirty-two complications were classified as Clavien I, 29 as Clavien II, and 43 as Clavien I or II. One patient with obstructive pyelonephritis that required nephrostomy placement was classified as having IIIa [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ] and two patients with ureteral wall injuries were classified as having III complications [
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ]; two cases in the cohort of Chandramohan et al. [
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ] (IIIb) were readmitted with pain and fever due to ureteric stone fragments and required URS for the clearance of steinstrasse. One hydrocalyx surgical correction [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ] was considered Clavien IIIb. Finally, one case of postoperative sepsis requiring admission to the intensive care unit [
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      ] was classified as having Clavien IV.

      3.7 Ureteral injuries

      Twenty-one cases of ureteral injuries (1.59%) were noted in the whole cohort of pediatric patients. Smaldone et al. [
      • Smaldone M.C.
      • Cannon G.M.
      • Wu H.Y.
      • et al.
      Is ureteroscopy first line treatment for pediatric stone disease?.
      ] reported five cases of ureteral perforation or extravasation during surgical procedures treated with ureteric stent placement and one case of distal ureteral stricture requiring subsequent ureteral reimplantation. Wang et al. [
      • Wang H.H.
      • Huang L.
      • Routh J.C.
      • Kokorowski P.
      • Cilento B.G.
      • Nelson C.P.
      Use of the ureteral access sheath during ureteroscopy in children.
      ] observed four ureteral perforations with extravasation; 85.7% of these intraoperative complications occurred in the group of patients with UAS use. Erkurt et al. [
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ] noted two ureteral wall injuries, treated with stent insertion. One grade 1 intraoperative ureteral laceration was assessed by Yuruk et al. [
      • Yuruk E.
      • Tuken M.
      • Gonultas S.
      • et al.
      Retrograde intrarenal surgery in the management of pediatric cystine stones.
      ] during a procedure carried out with a UAS. One grade 1 ureteric lesion was detected in the cohort of Mosquera et al. [
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      ] and described using the classification for ureteric injuries provided by Traxer and Thomas [
      • Traxer O.
      • Thomas A.
      Prospective evaluation and classification of ureteral wall injuries resulting from insertion of a ureteral access sheath during retrograde intrarenal surgery.
      ]. This classification was also applied in the study by Chandramohan et al. [
      • Chandramohan V.
      • Siddalingaswamy P.M.
      • Ramakrishna P.
      • Soundarya G.
      • Manas B.
      • Hemnath A.
      Retrograde intrarenal surgery for renal stones in children <5 years of age.
      ] to one case of grade 1 (mucosal damage) and one case of grade 2 (submucosal damage) ureteric injuries during URS with UAS placement; both these patients required prolonged stenting for 4 wk. Lim et al. [
      • Lim E.J.
      • Traxer O.
      • Madarriaga Y.Q.
      • et al.
      Outcomes and lessons learnt from practice of retrograde intrarenal surgery (RIRS) in a paediatric setting of various age groups: a global study across 8 centres.
      ], in their global study of 314 pediatric patients from eight centers, reported five ureteric injuries (1.6%, three in the cohort of patients <5 yr old and two in the group of patients >10 yr old) and five cases of pelvicalyceal system injury (1.6%), all of them in patients <5 yr old. These were all noted postoperatively on retrograde pyelography and managed with a postoperative stent. Authors hypothesized that they might be explained by the minimal pelvicalyceal space of these younger patients. Finally, one grade 2 ureteral injury was reported in a cohort of eight cystinuric patients [
      • Quiroz Madarriaga Y.
      • Badenes Gallardo A.
      • Llorens de Knecht E.
      • Motta Lang G.
      • Palou Redorta J.
      • Bujons T.A.
      Can cystinuria decrease the effectiveness of RIRS with high-power Ho:YAG laser in children? Outcomes from a tertiary endourology referral center.
      ].

      3.8 Stone-free rates

      SFRs were evaluated in all the studies included in the analysis, even though significant heterogeneity emerged regarding follow-up timing schemes and diagnostic means. The definition of stone-free status varied among the studies. The overall SFR after a single URS procedure was 76.92%; after the second procedure, it went up to a mean of 84.9%. Six articles [
      • Jones P.
      • Rob S.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre.
      ,
      • Erkurt B.
      • Caskurlu T.
      • Atis G.
      • et al.
      Treatment of renal stones with flexible ureteroscopy in preschool age children.
      ,
      • Ferretti S.
      • Cuschera M.
      • Campobasso D.
      • et al.
      Rigid and flexible ureteroscopy (URS/RIRS) management of paediatric urolithiasis in a not endemic country.
      ,
      • Featherstone N.C.
      • Somani B.K.
      • Griffin S.J.
      Ureteroscopy and laser stone fragmentation (URSL) for large (≥1 cm) paediatric stones: outcomes from a university teaching hospital.
      ,
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      ,
      • Jones P.
      • Mishra D.
      • Agrawal M.
      • Griffin S.
      • Somani B.K.
      Outcomes of ureteroscopy vs mini-percutaneous nephrolithotomy for pediatric upper urinary tract calculi: comparative nonrandomized outcomes from two tertiary endourology referral centers.
      ] reported an SFR after a first and at least a second session of URS. These results are concordant with reported outcomes varying from 84% to 100% after a single ureteroscopic procedure [
      • Ishii H.
      • Griffin S.
      • Somani B.K.
      Flexible ureteroscopy and lasertripsy (FURSL) for paediatric renal calculi: results from a systematic review.
      ,
      • Resorlu B.
      • Sancak E.B.
      • Resorlu M.
      • et al.
      Retrograde intrarenal surgery in pediatric patients.
      ,
      • Whatley A.
      • Jones P.
      • Aboumarzouk O.
      • Somani B.K.
      Safety and efficacy of ureteroscopy and stone fragmentation for pediatric renal stones: a systematic review.
      ].

      3.9 Discussion

      One of the first applications of UAS in a pediatric cohort for the management of renal and ureteral stones was described by Singh et al. [
      • Singh A.
      • Shah G.
      • Young J.
      • Sheridan M.
      • Haas G.
      • Upadhyay J.
      Ureteral access sheath for the management of pediatric renal and ureteral stones: a single center experience.
      ] on eight patients with a mean age of 9.3 yr. The authors did not report any ureteral perforation or stricture, with a mean follow-up of 10 mo. However, only a few studies on relatively small cohorts exist investigating the role of the UAS placement in endoscopic treatment of pediatric renal stones. This is due to persistent concerns about the potential risk of intra- and postoperative complications associated with it, even though its high efficiency, minimal invasiveness, and repeatability are increasingly recognized [
      • Li J.
      • Yu H.
      • Zhou P.
      • et al.
      Application of flexible ureteroscopy combined with holmium laser lithotripsy and their therapeutic efficacy in the treatment of upper urinary stones in children and infants.
      ]. Studies focusing on analyzing the outcomes of UAS placement reported different conclusions. In the whole cohort including 1417 cases of pediatric URS with UAS placement, we reported 26 intraoperative and 130 postoperative complications, accounting for 1.8% and 9.18% of the overall procedures, respectively. Nevertheless, the use of a UAS did not cause any significant short- or long-term complication, as reported by the majority of these groups [
      • Berrettini A.
      • Boeri L.
      • Montanari E.
      • et al.
      Retrograde intrarenal surgery using ureteral access sheaths is a safe and effective treatment for renal stones in children weighing <20 kg.
      ,
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      ,
      • Aljumaiah S.
      • Allubly N.
      • Alshammari A.
      • Alkhamees M.
      • Bin H.S.
      Small ureteral access sheath in treating paediatric urolithiasis: a single centre experience.
      ,
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      ,
      • Singh A.
      • Shah G.
      • Young J.
      • Sheridan M.
      • Haas G.
      • Upadhyay J.
      Ureteral access sheath for the management of pediatric renal and ureteral stones: a single center experience.
      ].
      Treatment of pediatric stone includes a wide range of therapeutic options that should be evaluated and tailored to single patient needs. The goals of intervention in the pediatric population should always be to achieve a high SFR, preservation of renal function with minimally invasive approaches, and prevention of recurrence. Recent advancements in equipment technology and miniaturization, and the broader availability and application of holmium YAG laser to lithotripsy have rendered URS a valuable and attractive treatment modality in pediatric urolithiasis since its first description in 1988 by Ritchey et al. [
      • Ritchey M.
      • Patterson D.E.
      • Kelalis P.P.
      • Segura J.W.
      A case of pediatric ureteroscopic lasertripsy.
      ]. URS can be proposed as first-line therapy in most pediatric cases, particularly with associated ureteral stones or lower pole stones present, or in patients with cystinuria, who are less likely to benefit from SWL treatment [
      • Azili M.N.
      • Ozcan F.
      • Tiryaki T.
      Retrograde intrarenal surgery for the treatment of renal stones in children: factors influencing stone clearance and complications.
      ].
      Despite this, EAU guidelines on pediatric urology [

      Radmayr C, Bogaert G, Dogan HS, et al. EAU guidelines. Presented at the EAU Annual Congress Milan 2021. 2021.

      ] still present SWL as the first choice for treating most pediatric renal stones, although addressing concerns about SFRs and retreatment rates, both affected by the stone size, localization, type of lithotripter used, and Hounsfield units of the stone. Indeed, SWL often results in the need for multiple sessions of treatment, which in turn, require additional general anesthesia and extra radiation exposure. Therefore, PCNL is a better treatment option for larger and more complex stones, especially >20 mm in the renal pelvis or >10 mm in lower pole locations. PCNL is considered safe and effective in pediatric patients, with reported SFRs between 86.9% and 98.5% after a single session. However, it represents an invasive procedure that could result in significant complications, mostly bleeding, postoperative fever or infection, and persistent urinary leakage, thus exposing patients to the risk of blood transfusions, renal parenchymal loss, and longer inpatient stays. In this scenario, pediatric URS has been demonstrated to offer lower morbidity than PCNL and higher SFRs than SWL. Despite its minimally invasive nature, retrograde intrarenal surgery (RIRS) is not exempt from complications, even though in the cohorts analyzed, they were mostly low grade and transient [
      • Ishii H.
      • Griffin S.
      • Somani B.K.
      Ureteroscopy for stone disease in the paediatric population: a systematic review.
      ,
      • Azili M.N.
      • Ozcan F.
      • Tiryaki T.
      Retrograde intrarenal surgery for the treatment of renal stones in children: factors influencing stone clearance and complications.
      ].
      The use of UAS in the adult population has been well established: when placed into the proximal ureter or renal pelvis, it allows a safe, easy, and efficient passage of the flexible ureteroscope back and forth into the kidney. Therefore, using a UAS results in decreased operative time, costs, and morbidities related to ureteral injuries due to the ureteroscope [
      • Kaplan A.G.
      • Lipkin M.E.
      • Scales C.D.
      • Preminger G.M.
      Use of ureteral access sheaths in ureteroscopy.
      ]. A decrease in renal pelvic pressure during URS is considered one of the most beneficial effects of UAS placement, resulting in a reduced risk of postoperative septic complications in the treatment of complex cases and better visibility inside the pyelocalyceal system [
      • Tokas T.
      • Skolarikos A.
      • Herrmann T.R.W.
      • Nagele U.
      Pressure matters 2: intrarenal pressure ranges during upper-tract endourological procedures.
      ]. However, concerns have been raised about ureteral injuries due to UAS placement, with an acute ischemic effect on ureteral tissue and a subsequent onset of ureteral stricture [
      • Rizkala E.R.
      • Monga M.
      Controversies in ureteroscopy: wire, basket, and sheath.
      ]. Delvecchio et al. [
      • Delvecchio F.C.
      • Auge B.K.
      • Brizuela R.M.
      • et al.
      Assessment of stricture formation with the ureteral access sheath.
      ] investigated the long-term safety of UAS placement concerning ischemia-induced stricture formation, assessing a stricture rate of 1.4%, which was considered consistent with flexible URS without the assistance of the access sheath. Specific risk factors for stricture onset were identified; prior ureteral or retroperitoneal surgery, retroperitoneal radiotherapy, peripheral vascular disease, and collagen vascular disorders were demonstrated to affect the ureteral wall integrity. On the contrary, a review of the literature found no significant difference in SFRs, complication rates, and the number of procedures per patient either with or without a UAS for the treatment of large stones (>2 cm) [
      • Geraghty R.M.
      • Ishii H.
      • Somani B.K.
      Outcomes of flexible ureteroscopy and laser fragmentation for treatment of large renal stones with and without the use of ureteral access sheaths: results from a university hospital with a review of literature.
      ].
      With this systematic review of literature, we analyzed all case series reporting at least ten UAS cases in pediatric patients, and we aimed to gather all available evidence on its indications and outcomes. First, no clear indications on UAS usage emerge from the analyzed articles. None of them justified the choice of UAS placement based on a stone size threshold, stone location, age, or clinical characteristics of patients (weight, height, and comorbidities). Three studies were explicitly focused on the use of UAS [
      • Anbarasan R.
      • Griffin S.J.
      • Somani B.K.
      Outcomes and long-term follow-up with the use of ureteral access sheath for pediatric ureteroscopy and stone treatment: results from a tertiary endourology center.
      ,
      • Aljumaiah S.
      • Allubly N.
      • Alshammari A.
      • Alkhamees M.
      • Bin H.S.
      Small ureteral access sheath in treating paediatric urolithiasis: a single centre experience.
      ,
      • Mosquera L.
      • Pietropaolo A.
      • Brewin A.
      • et al.
      Safety and outcomes of using ureteric access sheath (UAS) for treatment of pediatric renal stones: outcomes from 2 tertiary endourology centers.
      ]. Most of the studies attempted the placement of UAS in all cases. However, in case of failure, surgeons either proceeded with flexible URS or put a temporary ureteric stent for passive dilatation of the ureter and postponed stone treatment. Regarding UAS calibers and lengths, 14 out of 22 (63.6%) studies showed a single-measure UAS positioned in every patient; five of 22 (22.7%) chose between two different calibers of UAS. This reveals that there is usually no planning based on preoperative variables and that, in most cases, surgeons decide the optimal strategy intraoperatively, considering the anatomy and wideness of the ureter.
      Similarly, there is no clear recommendation [

      Radmayr C, Bogaert G, Dogan HS, et al. EAU guidelines. Presented at the EAU Annual Congress Milan 2021. 2021.

      ] regarding passive dilatation with a preoperative stent prior to URS with or without UAS placement. The benefit of prestenting in the adult population has been elucidated comparing a cohort of prestented versus non-prestented patients undergoing a ureteroscopic stone intervention for significant stone burden (>1 cm) [
      • Chu L.
      • Sternberg K.M.
      • Averch T.D.
      Preoperative stenting decreases operative time and reoperative rates of ureteroscopy.
      ]. Their findings assessed that prestenting reduced operative time significantly during first URS and total operative time in case multiple sessions were required. Corcoran et al. [
      • Corcoran A.T.
      • Smaldone M.C.
      • Mally D.
      • et al.
      When is prior ureteral stent placement necessary to access the upper urinary tract in prepubertal children?.
      ] analyzed preoperative variables to predict the likelihood of successful primary ureteroscopic access to the upper urinary tract without previous stent placement in prepubertal children. Authors obtained a successful primary ureteroscopic access in 18/30 patients (60%), using an 8/10 Fr coaxial ureteral dilator in 29/30 (97%) and placing a 9.5 Fr UAS in 13 of these patients at the first attempt. Among the reasons for failed primary access to the upper urinary tract were a narrow ureteral orifice in three (25%), difficulty passing the iliac vessels in four (33%), a narrow ureteropelvic junction in three (25%), and anatomical anomalies in two (17%). After 1–2 wk of passive ureteral dilation with a ureteral stent, placement of a UAS was still unsuccessful in seven of 12 patients with unsuccessful primary ureteroscopic access. Interestingly, no age, weight, height, or body mass index differences was found between cases of successful and unsuccessful primary access to the upper urinary tract and between successful and unsuccessful placement of a UAS. Therefore, the authors suggested that ureteroscopic access to the upper tract without prior stent placement is achievable even in young children. The decision to place a stent and plan for subsequent URS after passive dilation represents a safe and effective approach, and should be stressed and shared with parents in preoperative counseling.
      Significant heterogeneity was found regarding the postoperative placement of a ureteral stent. A recent consensus statement on adult RIRS [

      Zeng G, Zhao Z, Mazzon G, et al. European Association of Urology Section of Urolithiasis and International Alliance of Urolithiasis Joint Consensus on retrograde intrarenal surgery for the management of renal stones. Eur Urol Focus. In press. https://doi.org/10.1016/j.euf.2021.10.011.

      ] recommended placing an internal ureteral stent after the procedure in most cases. Among the studies included in the analysis, this choice was based mainly on the duration of the procedure, number of passes with the ureteroscope, degree of ureteral trauma or edema visible after the procedure, and presence of residual calculi. Moreover, an indwelling ureteral stent was left in situ in patients at an increased risk of complications (eg, ureteral trauma, bleeding, or perforation) based on the surgeon's discretion. The use of strings on ureteral stents to avoid the need for additional general anesthesia was usually decided according to the surgeon's assessment of the family's ability to comply [
      • Kim S.S.
      • Kolon T.F.
      • Canter D.
      • White M.
      • Casale P.
      Pediatric flexible ureteroscopic lithotripsy: the Children’s Hospital of Philadelphia experience.
      ].
      Despite the efficacy and good outcomes of URS, with increasing stone size, SFR decreases and the number of procedures required to achieve stone-free status increases. Few articles directly compared SFRs after URS with or without UAS placement. Wang et al. [
      • Wang H.H.
      • Huang L.
      • Routh J.C.
      • Kokorowski P.
      • Cilento B.G.
      • Nelson C.P.
      Use of the ureteral access sheath during ureteroscopy in children.
      ] found that UAS use was not associated with an improved SFR; likewise, other few studies noted similar outcomes with and without a UAS [
      • Kourambas J.
      • Byrne R.R.
      • Preminger G.M.
      Dose a ureteral access sheath facilitate ureteroscopy?.
      ,
      • De Sio M.
      • Autorino R.
      • Damiano R.
      • Oliva A.
      • Pane U.
      • D’Armiento M.
      Expanding applications of the access sheath to ureterolithotripsy of distal ureteral stones. A frustrating experience.
      ]. By contrast, UAS placement was associated with a better SFR [
      • L’esperance J.O.
      • Ekeruo W.O.
      • Scales C.D.J.
      • et al.
      Effect of ureteral access sheath on stone-free rates in patients undergoing ureteroscopic management of renal calculi.
      ]. However, none of these studies was conducted in a pediatric cohort of patients, and the absence of randomized trials makes it impossible to quantify the effect of UAS placement on SFR.

      3.10 Limitations

      We collected all evidence from literature regarding UAS use during URS in the pediatric population, focusing on the rate of pre- and postoperative stenting, operative time, intra- and postoperative complications, and rate of stone-free status. Additionally, cases of ureteral injuries were reported and analyzed. Despite this, the most significant part of the articles showed general data on the outcomes of URS in the pediatric population and was not explicitly tailored on assessing the impact of a UAS on intra- and postoperative variables. Moreover, we found no RCT comparing the outcomes of URS with versus without a UAS. Therefore, trends and evidence of UAS usage might be derived only from data described within these cohorts.
      We could relate complications and ureteral injuries to UAS placement only when reported explicitly by authors. For this reason, the association between UAS use and outcomes and complications is difficult to quantify, and prospective clinical trials of larger sample sizes with standardized outcomes and longer follow-up durations are warranted to obtain more robust evidence on UAS. With newer, more powerful laser and advanced techniques, larger stones are now treated via URS, although in the absence of the type of power laser in all studies; this was difficult to compare [
      • L’esperance J.O.
      • Ekeruo W.O.
      • Scales C.D.J.
      • et al.
      Effect of ureteral access sheath on stone-free rates in patients undergoing ureteroscopic management of renal calculi.
      ]. The assessment of SFRs and other variables was also not standardized, and perhaps there is a need for this in the future to compare and contrast techniques and outcomes.

      4. Conclusions

      Flexible URS and laser lithotripsy is a safe and effective treatment option for pediatric urolithiasis. So far, no recommendation on UAS placement in pediatric URS exists, and it is not clear whether it improves SFRs. UAS use was associated with a low rate of ureteric injuries, mostly treated and resolved with a temporary indwelling ureteric stent. Further prospective and comparative studies on a larger cohort are warranted to assess the outcomes of UAS placement.
      Author contributions: Bhaskar K. Somani had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
      Study concept and design: Somani.
      Acquisition of data: Ripa.
      Analysis and interpretation of data: Ripa.
      Drafting of the manuscript: Ripa, Somani.
      Critical revision of the manuscript for important intellectual content: Tokas, Griffin, Ferretti, Tur, Somani.
      Statistical analysis: Ripa.
      Obtaining funding: None.
      Administrative, technical, or material support: None.
      Supervision: Griffin, Somani.
      Other: None.
      Financial disclosures: Bhaskar K. Somani certifies that all conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript (eg, employment/affiliation, grants or funding, consultancies, honoraria, stock ownership or options, expert testimony, royalties, or patents filed, received, or pending), are the following: None.
      Funding/Support and role of the sponsor: None.

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