Feasibility of flexible and navigable suction ureteral access sheath in pediatric ureteroscopy: A systematic review from the European Association of Urology Section of Endourology

Abstract

Objective

The introduction of a flexible and navigable suction ureteral access sheath (FANS-UAS) has further enhanced retrograde intrarenal surgery (RIRS) by improving kidney stone clearance and reducing operative challenges. However, evidence for its use in the pediatric population remains sparse. Thus, this systematic review focuses on the current evidence on the use of a FANS-UAS during RIRS in children with renal stones.

Methods

A systematic search of PubMed, Cochrane Library, and Google Scholar was conducted in May 2025 following the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines and PROSPERO registration (CRD420251049140). Studies were included if they reported original data on the use of a suction ureteral access sheath (UAS) during RIRS in pediatric patients (<18 years). Data on patient demographics, stone characteristics, surgical outcomes, and complications were extracted and analyzed descriptively.

Results

Out of 49 screened studies, three met the inclusion criteria, including 74 pediatric patients. A FANS-UAS was used in all cases, with 97% utilizing 10/12 Fr UAS and 91% employing a 7.5 Fr flexible ureteroscope. The pooled stone-free rate was 99%, with complications limited to minor ureteral injury (4.1%) and Clavien–Dindo Grade I/II events (9.5%). One study showed the superiority of a FANS-UAS over a conventional UAS in operative time and initial stone-free rate. However, the evidence was limited by small sample sizes and heterogeneity.

Conclusion

RIRS with a FANS-UAS a is a safe and effective option for managing pediatric urolithiasis, including large and multiple stones. Nevertheless, current evidence is based on a small number of studies with limited generalizability. Further prospective research is needed to validate these findings, to explore the role of suction, and to investigate various UAS and endoscope configurations.

1. Introduction

Pediatric urolithiasis is a polyetiological nosology characterized by increasing prevalence and significant recurrence, which explains the considerable pressure on healthcare worldwide [1]. Particularly problematic is the cohort of young patients under 18 years of age, who are characterized at baseline as high-risk patients due to more serious causes compared with adults, making the optimization of treatment of these patients particularly urgent [2]. According to the European Association of Urology guidelines, percutaneous nephrolithotripsy (PCNL) is the most frequently mentioned option, especially for large and multiple stones, which allows for a greater likelihood of adequate access to the renal cavity due to the smaller skin-to-kidney distance [3]. However, a notable disadvantage is the direct mechanical damage to the renal parenchyma, which is particularly undesirable due to the need for complete renal integrity in growing children [4]. This fact shifts the focus of specialists towards retrograde intrarenal surgery (RIRS), which often allows for achieving non-inferior results, especially with new technological innovations, including flexible and navigable suction ureteral access sheath (FANS-UAS) [5]. The advantages for urolithiasis treatment are mostly evident in adults and significantly improve kidney stone surgery outcomes by providing better stone removal, fewer complications, and faster recovery compared with the standard tool [6]. There are currently no systematic reviews on the use of suction technologies, particularly FANS-UAS, for pediatric patients with urolithiasis during RIRS, leaving the question of the efficacy and safety of these technologies in the pediatric cohort open. Thus, this review focuses on the use of a FANS-UAS during RIRS in children with urolithiasis.

2. Materials and methods

2.1. Search

In May 2025, we conducted a systematic search across several databases, including PubMed, Cochrane Library, and Google Scholar via Boolean operators using the following terms: “Ureteroscopy”, “URS”, “f-URS”, “URSL”, “retrograde intrarenal surgery”, “lithotripsy”, “kidney”, “renal”, “ureter”, “stone”, “adolescent”, “pediatric”, “children”, “suction”, “aspiration”, “ureteral access sheath”, “UAS”, “suction UAS”, “SUAS”, “FANS-UAS”.

2.2. Inclusion criteria

Studies were eligible for inclusion if they reported the use of FANS-UAS in pediatric patients with urolithiasis undergoing RIRS, irrespective of sample size. When studies evaluated multiple endourological interventions, they were included only if they explicitly reported the number of pediatric patients managed with RIRS and provided extractable outcomes for the RIRS group. To ensure procedural comparability, included reports were required to provide a description of the instruments used during the procedure. We considered English-language publications with full-text availability, including randomized and non-randomized clinical trials, cohort and case-control studies, as well as case series and case reports, with no restriction on publication date.

2.3. Exclusion criteria

Studies were excluded if they did not specifically describe the use of FANS-UAS in pediatric patients with urolithiasis undergoing RIRS. Reports evaluating multiple endourological techniques were omitted when the number of patients treated with RIRS and their corresponding outcomes could not be clearly identified. Studies lacking adequate information on patient demographics or stone characteristics were also excluded to ensure clinical relevance and comparability. In addition, editorials, narrative reviews, conference abstracts, opinion articles, and other non-original research publications were not considered. Finally, studies published in languages other than English were excluded from the analysis.

2.4. Study process

Two reviewers (Talyshinskii A and Juliebø-Jones P) independently identified all papers. All studies fitting the inclusion criteria were selected for full review. In cases of disagreement or discrepancy, the senior author (Somani B) made the final decision.

2.5. Data extraction and analysis

We systematically reviewed studies and extracted information related to the safety and outcomes of RIRS with FANS-UAS among patients under 18 years old. Specifically, we analyzed information regarding authors and year of publication, patient demographics and stone characteristics, modality used and specific suction technology, as well as outcomes, including at least complication rates and stone-free rates (SFRs). In addition, the shortcomings of the studies, as highlighted by the authors themselves, were also analyzed to provide a more objective understanding of the role of suction technologies for adolescent patients with urolithiasis in routine clinical practice. We did not plan to perform a meta-analysis; only a pooled analysis, calculating mean values of outcomes, was performed. This study is reported following the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines and has been registered in the PROSPERO database (CRD420251049140).

2.6. Quality of studies assessment

The Centre for Evidence-Based Medicine criteria were used to evaluate the levels of evidence of the included studies [7]. Among randomized and non-randomized clinical trials, the risk of bias was assessed via Cochrane's tools RoB 2 and ROBINS-I [8,9]. For the case reports and single-arm cohorts, methodological quality was assessed using the respective JBI Critical Appraisal Checklist [10].

3. Results

Among 49 studies, three met the inclusion criteria: one prospective multicenter single-arm study with 50 patients [11], one retrospective single-center matched-pair analysis [12] with 23 patients, and one case report with one patient [13] (Fig. 1). Among the 74 pediatric patients, the mean age was 9.9 years and ranged from 1 year to 17 years. The preschool subgroup (defined as <5 years in Gauhar et al. [11] and as 1–6 years in Turedi and Sezer [12]) was prominent in both cohort studies and accounted for 30% of the total cohort, with 62% of all 74 patients being male. The indications for RIRS with a FANS-UAS varied among studies, with only Gauhar et al. [11] reporting specific indications as a percentage. Thus, flank pain was the most common indication, present in 66% of patients. Next, febrile urinary tract infection was present in 20% of cases, which was also mentioned in a case report by Cheng et al. [13] and in a study by Turedi and Sezer [12], but without specifying the frequency of occurrence. Gauhar et al. [11] further mentioned incidental detection (10%) and gross hematuria (4%). Other authors also mentioned residual fragments (RFs) after other interventions as indications for RIRS with a FANS-UAS [12,13]. All studies used non-contrast CT as preoperative imaging, but Gauhar et al. [11] used a lower-dose protocol, representing 68% of the pooled cohort. Stones were localized in the upper pole, middle pole, lower pole, or renal pelvis in 16%, 28%, 24%, and 20% of cases, respectively; multiple stones were present in 11% of cases in the pooled cohort. Only two studies described stone density and used different approaches, which hinders their generalizability. For example, in the cohort by Turedi and Sezer [12], mean stone density was 878.1 (standard deviation [SD] 261) Hounsfield units, whereas in the Gauhar et al. [11] cohort, 34% of patients had stones with density >1000 Hounsfield units [11,12]. In 50% of the pooled cohort, 1–2 cm stones prevailed (Table 1).

Figure 1.

Preferred Reporting Items for Systematic reviews and Meta-Analyses flowchart for literature search.

Table 1.

Patient demographics and stone characteristics across included studies.

Study	Type of study	Patient, n	Agea, year	Preschool subgroupb	Male, %	Stone location, %	Stone size, %
Gauhar et al., 2024 [11]	Prospective multicenter single-arm study	50	6.6±3.4 (1–15)	30	66	-Upper pole only: 18 -Middle pole only: 32 -Lower pole only: 22 -Renal pelvis only: 20 -Multiple locations: 8	-<1 cm: 40 -1–2 cm: 48 ->2 cm: 12
Turedi and Sezer, 2025 [12]	Retrospective single-center matched-pair analysis	23	10.2±6.1 (1–17)	30	52	-Upper pole only: 13 -Middle pole only: 22 -Lower pole only: 26 -Renal pelvis only: 22 -Multiple locations: 17	-<1 cm: 35 -1–2 cm: 52 ->2 cm: 13
Cheng et al., 2025 [13]	Case report	1	13	0	100	-Lower pole: 100	- 1.1 cm: 100
Summary	–	74	9.9 (1–17)	30	62	-Upper pole only: 16 -Middle pole only: 28 -Lower pole only: 24 -Renal pelvis only: 20 -Multiple locations: 11	-<1 cm: 38 -1–2 cm: 50 ->2 cm: 12

–, not applicable.

^aValues are presented as mean±standard deviation (range); summary values are presented as weighted mean (range).

^bPreschool subgroup was defined as age <5 years in Gauhar et al. [11] and as 1–6 years (preschool age) in Turedi and Sezer [12].

The overall pre-stenting rate was 85%; however, subgroup analysis was performed only by Turedi and Sezer [12], in whose cohort pre-stenting was performed in all preschool children. A ureteral access sheath (UAS) 10/12 Fr was used in the majority of cases (98%), with UAS 11/13 Fr used in 2% of the cohort by Gauhar et al. [11] and in the case report by Cheng et al. [13]. The flexible ureteroscope used was disposable in 86% of the cases. In terms of diameter, the 7.5 Fr flexible ureteroscope was used in 91% of the cases. Sheath placement success was 100% across all three studies; however, only Gauhar et al. [11] noted that while suction worked in all cases, complete navigation to all calyces was achieved in 94%. The Holmium:YAG laser at 30 W, 40 W, or 100 W was used in all studies, whereas the thulium fiber laser was also mentioned by Gauhar et al. [11] and Turedi and Sezer [12]. Gauhar et al. [11] reported dusting, fragmentation, and their combination in 58%, 24%, and 18% of cases, respectively, while Turedi and Sezer [12] mentioned both techniques without specifying their rates of use, and Cheng et al. [13], in their case report, described fragmentation with a 1 J×20 Hz setting. Operative time (OT) was reported in only two papers [11,12], with a weighted mean OT of 47.4 (weighted SD 20.8) min. Meanwhile, length of stay (LOS) was described in all studies and was characterized by minimal differences. Thus, in the prospective study by Gauhar et al. [11], mean LOS was 2.08 (SD 0.72) days; in the case report by Cheng et al. [13], LOS was 2 days; while in the retrospective study by Turedi and Sezer [12], mean LOS was slightly shorter and was 1.6 (SD 1.8) days (Table 2).

Table 2.

Preoperative and postoperative characteristics.

Study	Preoperative imaging	Pre-stenting, %	Instrument	Sheath placement success, %	Laser type	Stone fragmentation technique	Operation timea, min	Length of staya, day	SFR, %	Ureteral injuryb, %	Complication ratec, %
Gauhar et al., 2024 [11]	Low-dose NCCT	96	•UAS: ClearPetra® (Wellead, Panyu, Guangzhou, China); 10/12 Fr (98%) and 11/13 Fr (2%) • fURS - 7.5 Fr (88%) - Disposable (80%)	100	Holmium:YAG 40/100 W or TFL	Dusting: 58%; fragmentation: 24%; combination: 18%	46.02±20.72	2.08±0.72	100	Grade 1: 4.0	I–II: 8.0
Turedi and Sezer, 2025 [12]	Standard NCCT	65	•UAS: ClearPetra® (Wellead, Panyu, Guangzhou, China); 10/12 Fr (100%) •fURS: disposable 7.5 Fr (100%)	100	Holmium:YAG 30 W or TFL 60 W	Dusting or fragmentationd	50.4±21.1	1.6±1.8	96	Grade 1: 4.3	I–II: 13
Cheng et al., 2025 [13]	Standard NCCT	No	•UAS: YiGaoMED® (China); 11/13 Fr •fURS: disposable 8.4 Fr	100	Holmium:YAG	Fragmentation	n/a	2	100	0	0
Summary	Standard NCCT: 32%; low-dose NCCT: 68%	85	• UAS - 10/12 Fr (97%) - 11/13 Fr (2.7%) • fURS - 7.5 Fr (91%) - Disposable (86%)	100	Holmium:YAG 30/40/100 W or TFL	n/a	47.4±20.8	1.93±1.18	99	Grade 1: 4.1	I–II: 9.5

NCCT, non-contrast CT; SFR, stone-free rate; UAS, ureteral access sheath; fURS, flexible ureteroscope; TFL, thulium fiber laser; n/a, not available.

^aValues are presented as mean±standard deviation.

^bAccording to Traxer classification; summary values are presented as weighted mean (weighted standard deviation).

^cAccording to Clavien–Dindo classification.

^dNo percentage of stone fragmentation technique was provided in the corresponding original study.

In terms of the efficacy of RIRS with a FANS-UAS, the pooled SFR was 99%. The pooled Clavien–Dindo Grade I–II complication rate after surgery was 9.5%. In the study by Gauhar et al. [11], complications were observed in four patients in the form of transient fever and hematuria. In the study by Turedi and Sezer [12], three patients had hematuria or urinary tract infection; in both studies, these minor complications were self-limited or managed conservatively [11,12]. The case report by Cheng et al. [13] specifically noted no postoperative complications. Ureteral injury according to the Traxer classification was present in 4.1% of the pooled cohort and corresponded to Grade 1 (Table 2).

One study had a non-randomized design and was assessed using the ROBINS-I tool and had a moderate risk of bias [12] (Table 3). Bias due to confounding (Domain 1) was related to the absence of a control group for potential confounding despite the presence of a comparator group. Selection bias was also noted due to the absence of pre-defined selection strategies. Lack of blinding among clinicians and outcome assessors introduced moderate risk of bias due to deviations from intended interventions and bias in outcome measurement. The other two studies fulfilled all criteria of the relevant JBI Critical Appraisal Checklist for the case report [13] and the single-arm study [11], respectively (Table 4).

Table 3.

Domain-level risk of bias assessment using ROBINS-I and distribution of domain-level ratings.

Study	D1	D2	D3	D4	D5	D6	D7	Overall risk of bias
Turedi and Sezer [12]	Moderate	Moderate	Low	Moderate	Low	Moderate	Low	Moderate

D, domain; D1, bias due to confounding; D2, bias due to selection of participants; D3, bias in classification of interventions; D4, bias due to deviations from intended interventions; D5, bias due to missing data; D6, bias in measurement of outcomes; D7, bias in selection of the reported result.

Table 4.

Domain-level risk of bias assessment using JBI Critical Appraisal Checklist [10].

Study (assessment item)	Outcome
Cheng et al. [13]
1. Were the patient's demographic characteristics clearly described?	Yes
2. Was the patient's history clearly described and presented as a timeline?	Yes
3. Was the current clinical condition of the patient on presentation clearly described?	Yes
4. Were diagnostic tests or assessment methods and the results clearly described?	Yes
5. Was the intervention(s) or treatment procedure(s) clearly described?	Yes
6. Was the post-intervention clinical condition clearly described?	Yes
7. Were adverse events (harms) or unanticipated events identified and described?	Yes
8. Does the case report provide takeaway lessons?	Yes
Gauhar et al. [11]
1. Were there clear criteria for inclusion in the case series?	Yes
2. Was the condition measured in a standard, reliable way for all participants included in the case series?	Yes
3. Were valid methods used for identification of the condition for all participants included in the case series?	Yes
4. Did the case series have consecutive inclusion of participants?	Yes
5. Did the case series have complete inclusion of participants?	Yes
6. Was there clear reporting of the demographics of the participants in the study?	Yes
7. Was there clear reporting of the clinical information of the participants?	Yes
8. Were the outcomes or follow-up results of cases clearly reported?	Yes
9. Was there clear reporting of the presenting site(s)/clinic(s) demographic information?	Yes
10. Was statistical analysis appropriate?	Yes

4. Discussion

The first significant results of RIRS in children with nephrolithiasis were published in 2007, when Cannon et al. [14] reported 76% SFR among children with lower-pole renal calculi. Subsequently, certain risk factors leading to RFs have been identified. Thus, according to one of the largest series on pediatric stones published by Juliebø-Jones et al. [15], RIRS can be performed in pediatric cases with large and multiple stone burdens. Still, the complication rate is significantly higher compared with that for smaller stones. In addition, total operation time, stone size, and multiplicity were significant predictors of RFs [15]. In another interesting study, Tanidir et al. [16] revealed that large stone size is an independent risk factor for RFs after RIRS, regardless of UAS use. Despite the fact that the incidence of pediatric urolithiasis is relatively low, it is frequently associated with metabolic or anatomical disorders or infectious conditions, for which reason there is a high possibility of post-therapeutic recurrence, which, together with the risk of RFs in large and multiple stones, explains the frequent performance of percutaneous interventions in this cohort of patients, especially after the improvement and miniaturization of endoscopes [17]. Therefore, according to Mahmoud et al. [18], mini-PCNL is more cost-effective for pediatric renal stones 10–30 mm in size. According to a recent meta-analysis by Yuan et al. [19], micro-PCNL excelled in SFR (p=0.003), postoperative fever rates (p=0.02), and Clavien–Dindo Grade II complications (p=0.05). These trends align with current guidelines, which recommend percutaneous interventions specifically for large stones, regardless of their localization [20]. Nevertheless, the formation of percutaneous access directly disrupts the integrity of the renal parenchyma, which in itself is associated with the risk of bleeding and damage to adjacent structures, and can logically lead to some changes in the functional activity of the parenchyma, primarily when these procedures are performed frequently. This risk is emphasized in adults but is particularly relevant for highly recurrent pediatric urolithiasis [21,22].

This fact determines the necessity to improve other endourological modalities, to which RIRS belongs. Indeed, since its introduction, this procedure has undergone several changes and has been enhanced by numerous innovations, which now enable RIRS to be placed on the same level as PCNL in terms of efficiency and to expand the indications for performing the former. In addition to the miniaturization and improvement of endoscope characteristics, particularly noteworthy is the development of suction technologies, which enable the preservation of the visibility of the operative field and the removal of small concretions, directly affecting the duration of the procedure and its overall success [23,24]. Thus, this technology is currently implemented globally in two variations: in-scope and out-of-scope. The advantage of the first approach is independence from the presence of UAS; however, direct-in-scope suction technology is significantly limited by the size of the instrument's working channel, which is its main barrier and makes the second way of suction technology implementation—in the form of FANS-UAS—more attractive [25,26]. In addition to the possibility of better aspiration due to the larger diameter of the UAS compared with the fURS working channel, it is also possible to guide the UAS into a specific small calyx, allowing for direct aspiration of fragments after stone fragmentation and saving time, which in itself affects the SFR when performing RIRS. According to Peng et al. [27], flexible ureteroscopy using a tip-flexible pressure-controlling UAS is safe and effective for renal stones in children. According to Zhu et al. [28], FANS-UAS exhibited superior performance compared with traditional UAS, demonstrating higher SFR, reduced postoperative fever rate, and improved quality of life outcomes. This confirms that the flexible tip and suction port are two distinct innovations, each offering its benefits. Together, they enhance one another's effectiveness, making FANS-UAS more than just an upgrade. Instead, it represents a comprehensive advancement that reduces the previously established advantages of PCNL over RIRS when standard UAS was used [15]. Indeed, according to a recent meta-analysis by Tzelves et al. [29], when mini-PCNL was compared with flexible ureterorenoscopy with suction, no differences were found in terms of SFRs and infectious complication rates. Despite the above, it is essential to note that all studies included adult patients, which limits the applicability of extrapolating the benefits of FANS-UAS to other patient cohorts, such as children.

In a recent scoping review, all data regarding the use of suction- or vacuum-assisted mini-PCNL or RIRS in children and adolescents with kidney stones were pooled, and it was shown that as of 2024, there were very few data to draw any conclusions, especially in the context of RIRS [5]. Nevertheless, several studies have since been published on suction technologies for pediatric RIRS, which need to be updated and consolidated to advance this direction and identify further research directions. To the best of our knowledge, we have attempted, for the first time, to conduct a systematic review of pediatric RIRS-related suction technologies, resulting in only three studies on this topic. Notably, all of these studies focus on FANS-UAS, suggesting that interest in the benefits of suction gained prominence with the introduction of FANS-UAS, particularly in the context of disposable endoscopes, which accounted for 86% of the pooled cohort. There is a clear gap in the literature, as no studies have explored other suction techniques in RIRS or ureteroscopy more broadly.

According to the pooled results, the SFR was 99%, confirming the improved efficiency of RIRS with the development of related technologies, specifically FANS-UAS. The pre-stenting rate was 85%, indicating the possibility of performing RIRS without pre-stenting, even for the pediatric cohort; this is largely due to the miniaturization and modernization of instruments, and confirmed by a pooled ureteral injury rate of only 4.1%. It is noteworthy that in two studies, the youngest patients were 1 year old, and no procedure failure was reported in these patients, suggesting the suitability of RIRS with FANS-UAS for all pediatric subgroups. The conventional pediatric UAS is typically 9.5 Fr, which is smaller than the aforementioned FANS-UAS (10/12 Fr) and may seem to be a notable advantage, especially among preschool children. However, a FANS-UAS is characterized by its advantages that may outweigh the above, especially for stones >1 cm. The ability to remove fragments and dust is enhanced by simultaneous and controlled aspiration, allowing the maintenance of visibility of the operative field and minimizing the risk of a significant increase in intrarenal pressure, resulting in a reduction in operative duration, renal damage, and postoperative infection—which is particularly important in the pediatric cohort, as evidenced by the low postoperative complication rate and high SFR observed in the included studies. Moreover, the low incidence of ureteral injury according to the Traxer classification indirectly suggests the insignificance of diameter differences between a conventional pediatric UAS and a FANS-UAS for the pediatric cohort when combined with careful technique and appropriate pre-stenting.

Cases with stone size ≤2 cm or >2 cm were 88% and 12%, respectively, and this pooled SFR for pediatric RIRS of 99% emphasizes the increased feasibility of RIRS with a FANS-UAS, especially for multiple stones (11% of cases), which, as previously stated, were considered more achievable with PCNL rather than RIRS with a conventional UAS. Table 1 also shows that there is a relatively balanced frequency of stone localization in different calyceal groups or the pelvis, which is also not a barrier to the possibility of placement of a FANS-UAS in the target calyx. To summarize, RIRS with a FANS-UAS is now a reliable treatment option for children, even with multiple stones or stones greater than 2 cm. In the past, this scenario was a clear indication for PCNL, which demonstrated better results compared with RIRS using standard UAS; this remains specified in current guidelines [20]. However, in pediatric urology, it is generally accepted and justified to separate preschool children (<5 years or <6 years) from older children when reporting outcomes of different interventions. Preschool children have a narrower ureter with increased vulnerability to instrumentation injury. Both cohort studies report the number of preschool patients, which accounted for 30% of the final sample, with Turedi and Sezer [12] further emphasizing their pre-stenting placement in all preschool patients and Gauhar et al. [11] reminding readers of the variability in renal collecting system capacity across age groups. However, the papers do not provide separate results for this age group, which means we can only apply the combined results to all patients younger than 18 years without being able to rule out RFs and complications in the preschool group. In addition to age, gender must also be considered in pediatric urology. In boys, the urethra is longer and narrower and has a curved trajectory, which may increase the difficulty of UAS placement in addition to the above-mentioned risks. In our review, neither cohort study provided separate results for males, who made up 62% of the total sample, which means we cannot identify risks for specific subgroups when looking at the overall results for all patients under 18 years old.

Other limitations of the available works and the weaknesses of the pooling of results should also be noted, which are also the shortcomings of this systematic review. First, there are currently only three studies that have been conducted directly to determine the benefits of suction techniques during pediatric RIRS. However, in the context of systematic reviews, even with meta-analysis, there is no consensus on a clear minimum number of included studies, and it is possible to conduct them based on two or more publications, which makes this shortcoming less critical [30]. Second, all suction-related studies are focused on a FANS-UAS, which undoubtedly reduces heterogeneity between studies and makes pooled results more reliable; however, we can draw conclusions only about the FANS-UAS and not about suction technologies for pediatric RIRS in general. In particular, the advantages of a FANS-UAS over direct-in-scope suction and the results of their combined use for pediatric RIRS are not known [31]. Moreover, we can currently draw conclusions based not just on a FANS-UAS, but primarily on the use of 10/12 Fr UAS with 7.5 Fr endoscopes, which are mentioned in 97% and 91% of cases, respectively. Third, due to the small initial number of case studies, we included all available studies regardless of the number of patients included. Thus, one of the three publications is a case report with the results of the treatment of an 11-year-old male patient, which is certainly not acceptable when performing a meta-analysis and lowers the level of evidence of our systematic review. Nevertheless, all final calculations were performed correctly, and, in such an understudied topic, the treatment outcomes of each patient are essential to gain an initial understanding of the pros and cons of a FANS-UAS for pediatric RIRS. Moreover, given the publication dates of the included studies, this review can be characterized as up-to-date [32]. Fourth, we limited ourselves to pooled analyses or outcomes summarized as initially registered in PROSPERO (CRD420251049140) and decided to fully comply with the originally defined methodology to ensure an unbiased study [33]. Fifth, the final number of patients is very small (n=74), which also reduces the reliability of the pooled results due to the increased risk of overestimating intervention effects [34]. Sixth, only three studies included a purely pediatric cohort, and a detailed examination of many papers reveals that the calculation of mean age and SD hypothetically includes patients younger than 18 years old, especially if being younger than 18 years old was not a criterion for exclusion from the study [35]. In this case, results are reported for the entire cohort, thereby reducing the applicability of results for patients <18 years or ≥18 years of age and potentially leading to selection or information bias in our review [36].

In interpreting these findings, several important limitations must be acknowledged. First, data on kidney stone composition and metabolic evaluation were not available, while reporting of kidney stone density was inconsistent: Gauhar et al. [11] noted that 34% of patients had kidney stones >1000 HU, whereas Turedi and Sezer [12] provided mean density values with no difference between groups, precluding pooled analysis. Similarly, Keat et al. [37] showed that kidney stones with a high HU (>1000 HU) were associated with a higher frequency of RFs, and the thulium fiber laser was more effective compared with the Holmium:YAG laser. This can directly affect the OT, which itself can be a risk factor for RFs and post-procedural complications [38]. Given that higher HU values and certain kidney stone types are known predictors of RFs, their omission is a key gap. Similarly, although all included studies used the Holmium:YAG laser, with limited mention of TFL, no outcomes were stratified by laser type or settings, despite adult data suggesting that TFL may be associated with shorter OT.

The effect of pre-stenting also remains uncertain: while overall rates were high (85%), only one study provided subgroup data (all preschool children pre-stented), and pooled outcomes do not allow the determination of whether pre-stenting improved SFRs or reduced complications in specific subgroups. Beyond technical variables, no included study reported cost-related outcomes. The adult RIRS literature suggests comparable costs to extracorporeal shock wave lithotripsy [39], but pediatric data, and especially FANS-UAS cost analyses, are lacking. Indirect comparison suggests that RIRS with a FANS-UAS may offer efficacy similar to mini-PCNL (pooled SFR of 99%) but with reduced risk of parenchymal trauma and bleeding, and superior outcomes compared with extracorporeal shock wave lithotripsy, which often requires multiple sittings and is less effective for stones >1 cm in diameter or lower-pole stones. However, the absence of head-to-head pediatric trials limits firm conclusions. OT (reported in two studies, weighted mean 47.4 min) and the number of sittings were inconsistently described, yet both represent important confounders, as they are influenced by stone burden, location, density, and surgeon experience while also affecting complications and SFRs [40]. Future studies should therefore stratify outcomes by stone density, laser type, pre-stenting, OT, and the number of sittings, while incorporating cost-effectiveness and comparative analyses with PCNL and extracorporeal shock wave lithotripsy to better define the role of a FANS-UAS in pediatric stone management.

Finally, there are individual shortcomings related to the design of the included studies. Thus, one study, presented as a single-arm trial [11], is limited by the inability to meet the requirements of randomization and blinding, and to exclude the influence of other factors on the results, thereby limiting its evidence value [41]. Other studies have a control group and an experimental group, but are single-center and retrospective, which also have their own disadvantages [12,42]. Thus, despite promising results, they are based on a small number of studies with a small number of patients and are mainly based on the use of a 10/12 Fr UAS with the 7.5 Fr endoscope, which limits the reliability and reproducibility of the results and emphasizes the need for further study of FANS-UAS technology in different device combinations when performing pediatric RIRS. Compared with the earlier data, our current review of a FANS-UAS shows a markedly high SFR and a lower complication profile [43]. The importance of technological adjuncts such as FANS-UAS must be acknowledged in other difficult patient groups such as pregnancy and the obese patient groups [44].

The level and certainty of evidence across analyzed studies, which define related indicators of the final systematic review, should be specified. The evidence varied between Level 2b and Level 4, according to the Oxford Centre for Evidence-Based Medicine. The overall systematic review was at Level 2b, considering that it relied on observational and non-randomized studies with no comparative high-level data. At the same time, the Grading of Recommendations, Assessment, Development and Evaluation system assessed the evidence certainty as “Low” for all three studies that were included. The uniform rating was derived from methodological deficiencies such as risk of bias, lack of randomization, failure to control for confounders, and the intrinsically limited generalizability of a single case report (Fig. 2).

Figure 2.

Level and certainty of evidence across included studies and for this systematic review according to OCEBM and GRADE. OCEBM, Oxford Centre for Evidence-Based Medicine; GRADE, Grading of Recommendations, Assessment, Development and Evaluation.

5. Conclusion

Available data suggest that RIRS with a FANS-UAS is a safe and effective option for children, even in cases involving large or multiple kidney stones, which are traditionally managed with PCNL. However, the limited number of small, methodologically diverse studies lowers the overall quality of evidence and highlights the need for further research.

Author contributions

Study concept and design: Ali Talyshinskii, Patrick Juliebø-Jones, Bhaskar Somani.

Data acquisition: Ali Talyshinskii, Patrick Juliebø-Jones.

Data analysis: Ali Talyshinskii, Patrick Juliebø-Jones.

Drafting of the manuscript: Ali Talyshinskii, Patrick Juliebø-Jones.

Critical revision of the manuscript: Vineet Gauhar, Steffi Kar Kei Yuen, Selcuk Güven, Theodoros Tokas, Nariman Gadzhiev, Bhaskar Somani.

Conflicts of interest

The authors declare no conflict of interest.