Role of Minimally Invasive Percutaneous Nephrolithotomy Techniques—Micro and Ultra-Mini PCNL (<15F) in the Pediatric Population: A Systematic Review

Abstract

Introduction:

Management of pediatric stone disease is challenging, with standard percutaneous nephrolithotomy (PCNL) having a good stone-free rate (SFR), but with associated high complication rates. Miniaturization of this technique has led to the rise of minimally invasive PCNL techniques such as micro (<10F) and ultra-mini (<15F) PCNL procedures. Our objective was to perform a systematic review of the literature to evaluate the success and complication rates of minimally invasive PCNL techniques in the pediatric age group (<18 years).

Methods:

A Cochrane style search was performed and the following bibliographic databases were accessed: PubMed, Science direct, Scopus, and Web of Science. This was carried out in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.

Results:

A total of 14 studies (456 patients), including 8 on micro-PCNL (m-PCNL, n = 233) and 6 on ultra-mini PCNL (UMP, n = 223), were included. Mean stone size ranged from 12–16.5 mm (m-PCNL) and 12–41 mm (UMP), and the overall SFR ranged from 80% to 100% (m-PCNL) and 85% to 100% (UMP). The overall complication rates for all studies were 11.2%, which was slightly higher for UMP (13.9%). Postoperative renal colic or fragment obstruction was only seen in m-PCNL, but there was a statistically significant rate of extravasation or renal pelvicaliceal perforation and hematuria for UMP compared with m-PCNL.

Conclusion:

Miniaturized PCNL techniques can deliver high SFRs with a small risk of Clavien I/II complications. The size of tract seems to influence the nature of complications, with higher hematuria and renal extravasation with increasing tract size.

Introduction

The prevalence of urinary stone disease in children is rising.¹ Metabolic and anatomical factors play a major role in stone disease although there has also been a rise in incidental image-diagnosed stones.^2,3 Key objectives for surgical treatment include stone clearance and preservation of renal function while maintaining a low morbidity profile.

Since the inauguration of percutaneous nephrolithotomy (PCNL) in 1976, advancements in the technique and available equipment have continued.⁴ Miniaturization of technology through smaller access sheaths, optic puncture systems, and instruments have formed a part of this evolution.⁵ This innovation largely reflects the need to minimize tract-related morbidity from the traditional techniques using 26–32F tracts.³ In 1998, Jackman and colleagues reported initial use of the “mini perc” technique and successfully performed the procedure on children too.⁶ Later in 2011, Desai and colleagues described their experience with a 4.85F “all-seeing needle” and subsequently micro-PCNL (m-PCNL) was established.⁷ The concept of ultra-mini PCNL (UMP) was described as a new PCNL technique in 2013 using an 11–13F tract⁸

A critical appraisal of these minimally invasive PCNL techniques (<15F) and evaluation of their outcomes in children remains underreported. Therefore, our aim was to perform the first systematic review on this topic to provide an overview of the safety and feasibility of both m-PCNL and UMP in the pediatric population.

Methods

A systematic search was performed to identify studies on all PCNL techniques <15F (m-PCNL and UMP) published from inception of the technique until February 2017. This was undertaken in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) criteria and Cochrane guidelines. The search strategy was applied to the following bibliographic databases: Medline/PubMed, Science direct, Google Scholar, and Web of Science. Search terms included (but were not limited to): percutaneous nephrolithotomy, PNL, PCNL, pediatric, ultra-mini, micro, mini, and UMP. The following Medical subject headings (MeSH) were also used: [Nephrolithiasis], [Urologic Surgical Procedures], [Minimally Invasive Surgery], and [Child].

All studies that used a tract size <10F were classed as m-PCNL, whereas studies between 10 and 14F were classed as UMP.^5

–8

The inclusion criteria were as follows:

• Original studies reporting on m-PCNL and UMP in pediatric patients (<18 years of age)

• Instrument size <15F

• Minimum five patients reported in the study

We excluded articles on animal studies or on studies that included adults in the patient cohort.

There were no time or language restrictions set and all original study types were eligible, including randomized trials, cohort studies, and case series. Studies were required to report on at least five patients. Where multiple articles were published that reported from the same data set, only the most recent or comprehensive article was used.

Data extraction and outcomes of interest

Both the search process and the data extraction were undertaken by two authors (P.J., G.B.) independently and any discrepancy was clarified and sorted after arbitration by the senior author (B.K.S.). Primary authors of studies were contacted directly, where additional information or clarification was required.

Primary outcome measures:

• Initial and final stone-free rate (SFR)

• Complications, transfusion rates, and any other adverse events

Secondary outcome measures:

• Stone demographics

• Operative time duration

• Hospital stay

Additional information on patient demographics as well as inclusion/exclusion criteria outlined by each study was also collected. Studies were assigned a level of evidence in accordance with the Center for Evidence-Based Medicine (CEBM).⁹

Results

Our search yielded 163 studies, from which 14 satisfied our predefined inclusion/exclusion criteria.^{6,10

–22} Of these, 11 were retrospective and 3 were prospective studies, of which 6 studies were multicentric in their design.

Of the 14 studies included, 8 were m-PCNL (n = 233) and 6 (n = 223) were UMP studies (Tables 1 and 2).

Table 1.

Patient Demographics, Stone Size, Operative Time, and Hospital Stay Reported in the Studies

Author	Year published	Study type (level of evidence)	Sample size (male/female ratio)		Mean age - years (SD, range)		Instruments (F)	Mean stone size mm (SD)		Mean operation time minutes (SD)		Mean length of hospital stay in days (SD)
m-PCNL
Silay and colleagues¹⁰	2013	Prospective, multicenter cohort study (1b)	19 (6/13)		7.5 (4.4, 1–15)		4.85	14.8 (6.8, 7–32)		72.5 (NR)		1.8 (0.8, 1–3)
Bodakçi and colleagues¹¹	2015	Retrospective, single center cohort study (2b)	25 (14/11)		4.12 (5.33, 1–13)		4.85	13.45 (3.11, 8–20)		51.45 (30.69, 20–120)		3.1 (1.77, 2–7)
Dağgülli and colleagues¹²	2015	Prospective, single center cohort study (1b)	40 (19/21)		6.3 (4.4, 0.58–16)		4.85	16.5 (NR, 10–36)		75 (NR, 20–110)		3.8 (2, 1–10)
Karatag and colleagues¹³	2015	Retrospective, multicenter cohort study (2b)	56 (31/25)		7.63 (5.04,NR)		4.85	13.4 (3.4, NR)		57.1 (31.2, NR)		1.79 (0.64, NR)
Baş and colleagues¹⁴	2015	Retrospective, multicenter cohort study (2b)	45 (23/22)		5.62 (4.5, 1–15)		4.85	13.97 (3.46, 10–19)		57.11 (15.75, 25–85)		2.9 (0.92, 1–4)
Dundar and colleagues¹⁵	2016	Retrospective, single center cohort study (2b)	16 (8/8)		7.9 (NR, 2–16)		4.85	12.1 (4.3, 7.1–18.6)		37.2 (NR, 20–55)		1.5 (NR, 1–5)
Dede and colleagues¹⁶	2016	Retrospective, multicenter cohort study (2b)	24 (14/10)		1.3 (0.65, NR)		4.85	13.5 (3.84,NR)		53.7 (10.35,NR)		2.5 (0.8,NR)
Caione and colleagues¹⁷	2016	Retrospective, single center case series (4)	8 (3/5)		8.7 (NR, 1.5–17)		4.85	15 (NR, 12–20)		83 (NR, 42–122)		2.2 (NR, 1–3)
UMP
Jackman and colleagues⁶	1998	Retrospective, single center case series (4)	11 (NR)		3.4 (NR, 2–6.9)		11 (peel away vascular access kit–Cook urological)	12 (NR, 5–30)		203 (NR, 68–369)		6 (NR, 1–17)
Bilen and colleagues¹⁸	2007	Retrospective, single center cohort study (2b)	10 (7/3)		6.3 (NR, 4–8)		14	19 (NR, 9.7–35.2)		78 (NR, 40–120)		3.2 (NR, 2–4)
Bilen and colleagues¹⁹	2010	Retrospective, multicenter cohort study (2b)	N	T	N	T	14	N	T	N	T	N	T
			14 (6/8)	12 (10/2)	3.3 (NR, 1.5–6)	3 (NR,0.58–6)		41.6 (NR)	19.2 (NR)	93.5 (NR,40–180)	55.5 (NR, 30–130)	4.9 (NR,3–14)	3.1 (NR, 2–6)
Daw and colleagues²⁰	2015	Prospective single center cohort study (2a)	26 (15/11)		3.6 (1.3, 1.25–6)		14	19.61(11.29, 5–48)		71.08 (30.4, 25–150)		3.8 (2.078, 1–10)
Dede and colleagues²¹	2015	Retrospective, single center cohort study (2b)	39 (22/17)		5.8 (4.6, NR)		12	20.4 (7.6, NR)		56 (12.8, NR)		2.8 (0.42, NR)
Liu and colleagues²²	2016	Retrospective multicenter cohort study (2b)	111 (71/40)		3.9 (3.53, NR)		10	14 (6, 8–48)		39.4 (26.2, NR)		2.7 (1.51–7)

m-PCNL = micro-PCNL; N = nephrostomy; NR = not recorded; PCNL = percutaneous nephrolithotomy; T = tubeless; UMP = ultra-mini PCNL.

Table 2.

Showing Inclusion and Exclusion Criteria in These Studies

Author	Inclusion criteria	Exclusion criteria
m-PCNL
Silay and colleagues¹⁰	Shock wave-resistant stones <20 mm	History of open renal surgery
		Staghorn renal calculi
Bodakçi and colleagues¹¹	Stones irresponsive to SWL,	Untreated urinary tract infection
	Patients unwilling to undergo SWL treatment	Uncorrected coagulopathy
	Stones <20 mm	Staghorn renal calculi
Dağgülli and colleagues¹²	NR	NR
Karatag and colleagues¹³	Patient/parent preference (no further details)	NR
Bas and colleagues¹⁴	NR	Anomalous kidneys
		Bleeding diatheses
		Musculoskeletal deformities
		Stone size >20 mm
Dundar and colleagues¹⁵	SWL failure	Bleeding diatheses
		Musculoskeletal deformities
		Anomalous kidneys
Dede and colleagues¹⁶	NR	NR
Caione and colleagues¹⁷	Any upper tract stones (single or multiple)	Contraindications to general anesthesia
		Concomitant illness e.g., oncological disease
		Coagulation abnormalities
		Severe mental retardation
UMP
Jackman and colleagues⁶	NR	NR
Bilen and colleagues¹⁸	Age ≤16 years	NR
Bilen and colleagues¹⁹	NR	NR
Daw and colleagues²⁰	Age ≤6	Stones >5 cm
Dede and colleagues²¹	Stones resistant to SWL	NR
	Stones requiring repeated sessions of SWL
	Stones >20 mm.
Liu and colleagues²²	Stones resistant to and/or requiring multiple	NR
	Sessions for SWL and RIRS treatment
	Stones >20 mm
	Patient/parent preference

RIRS = retrograde intrarenal surgery; SWL = extracorporeal shockwave lithotripsy.

Micro-PCNL

In total, 233 patients with a mean age of 6.3 years and a male:female ratio of 1:1 underwent m-PCNL using the 4.85F all-seeing needle. The mean stone size in these studies ranged from 12 to 16.5 mm, with the youngest patient being 7-month old.¹² The renal pelvis was the commonest (46%) site of stone location. The mean operative time and hospital stay were 61 minutes and 2.5 days, respectively.

The mean initial and final SFR ranged from 67.5% to 92% and 80% to 100%, respectively in these studies (Table 3). The definition of SFR varied between studies (≤4, <4 or ≤3 mm) with three studies not providing how they defined SFR in their study. With the exception of one study, which solely used plain X-ray (XR) to assess for stone clearance, all others used XR in combination with ultrasound (US).

Table 3.

Stone-Free Rates and Complications Reported in the Studies

Author	Definition of stone free (mm)	Mean initial FR (%)		Mean final SFR (%)		Imaging modality to assess stone-free status	% transfused	Mean Hb drop (SD) g/L	Conversion	Double-J stent (%)/ ureteral catheter (%)/ nephrostomy (%)	Complication Rate (%)		Complications
m-PCNL
Silay and colleagues¹⁰	NR	NR		89.5		XR ±US	0	1 (3, NR)	2/19 to M-PCNL	21/0/0	15.7		Renal colic managed conservatively (2), Extravasation requiring percutaneous drainage (1)
Bodakçi and colleagues¹¹	≤4	92		NR		XR + US	0	4.6 (6.3, NR)	NR	12/80/8	12		Fever (2), Bleeding causing operation to be terminated (1)
Dağgülli and colleagues¹²	<4	67.5		80		XR ± US	0	7 (3,0–17)	2/40 to M-PCNL	27.5/72.5/0	30		Renal colic managed conservatively (7), Extravasation requiring percutaneous drainage (1)
Karatag and colleagues¹³	NR	82.1		92.8		XR + US	0	11 (19, NR)	NR	0/100/0	5.3		Renal colic requiring Double-J stent insertion (2), Extravasation requiring percutaneous drainage (1)
Baş and colleagues¹⁴	≤3	80		NR		XR + US	0	5.3 (8.7, NR)	0	26.7/77.3/0	13.3		Renal colic managed conservatively (3), Urinary infection (1), Fever (1), Renal colic requiring Double-J stent insertion (1)
Dundar and colleagues¹⁵	≤4	NR		93.8		XR + US	0	7.9 (4.9, NR)	0	16/84/0	0		Nil
Dede and colleagues¹⁶	<4	NR		83.3		XR + US	0	5.1 (3.4,NR)	0	17/83/0	25		Renal colic managed conservatively (4), Fever (2)
Caione and colleagues¹⁷	NR	87.5		100		XR	0	5 (4, NR)	1/8 conversion to RIRS	37.5/62.5/0	25		Haematuria resolving spontaneously (2)
UMP
Jackman and colleagues⁶	NR	NR		86		XR	0	NR	0	86/14/0	0		Nil
Bilen and colleagues¹⁸	NR	90		90		XR	0	6 (NR, 0–18)	0	30/NR/70	0		Nil
Bilen and colleagues¹⁹	NR	N	T	N	T	XR + US	0	15.4 (NR)	0	NR	N	T	N	T
		78.5	91.6	100	100						43%	0	Haemorrhage requiring blood transfusion (4), urinary infection (1), Extravasation requiring intervention (1)	Nil
Daw and colleagues²⁰	NR	76.9		85		XR	0	7.8 (8.6, 0–33)	1/26	16/84/100	23		Haematuria resolving spontaneously (1), fever (1) Haemorrhage requiring blood transfusion (1), Renal pelvis perforation (1), Urine leakage (2)
Dede and colleagues²¹	<3	82		87		XR + US	0	9 (6, 0–17)	NR	17/NR/NR	15.2		Urine leakage (2), Fever (4)
Liu and colleagues²²	<2	84.7		90.1		XR + US or NCCT	0	10.2 (7.1, 0–25)	NR	11.7/NR/NR	15.3		Haematuria resolving spontaneously (4), Minor pelvis perforation (3), Urine extravasation requiring intervention (3)

Hb = hemoglobin; M-PCNL = mini-PCNL; SFR = stone-free rate; US = ultrasound; XR = X-ray.

The mean drop in hemoglobin (Hb) was 5.9 g/L, and none of the patients required blood transfusion. None of the studies mentioned multiple punctures and/or supracostal access.

In total, 21 (9%) complications were reported across 233 patients included in this review (Table 4). The majority (81%, n = 17) of these were Clavien I and II complications, including conservative management of renal colic (62%, n = 13), and two patients each with fever and spontaneous resolution of hematuria. Clavien III complications (19%, n = 4) included two patients each with extravasation requiring percutaneous nephrostomy (PCN) and obstructing ureteral stone fragment requiring Double-J stent insertion. There were no Clavien IV/V complications reported during the review period.

Table 4.

Nature, Grade, Frequency, and Management of (Early) Complications

		Frequency			Management
Nature of complication	Clavien grade	Micro-PCNL (<10F) n = 233 (%)	Ultra mini PCNL (11–14F) n = 223	Overall N = 456 (%)	—
Fever	I	2 (0.9)	5 (2.2)	7 (1.5)	Conservative
Hematuria resolving spontaneously	I	2 (0.9)	5 (2.2)	5 (1.5)	Conservative
Urine leak resolving spontaneously	I	—	5 (2.2)	5 (1.1)	Conservative
Urinary tract infection	II		1 (0.4)	1 (0.2)	Oral antibiotics
Renal colic managed conservatively	II	13 (5.6)	—	13 (2.8)	Conservative
Hemorrhage requiring blood transfusion	II	—	5 (2.2)	5 (1.1)	Blood transfusion
Minor pelvis perforation	II	—	3 (1.3)	3 (0.6%	Double-J stent left in situ for 2/52
Fragment obstruction requiring Double-J stent insertion	III	2 (0.9)	—	2 (0.4)	Urgent Double-J stent insertion
Renal pelvis perforation requiring intervention	III	—	3 (1.3)	3 (0.6)	Percutaneous drainage
Extravasation requiring percutaneous drainage	III	2 (0.9)	4 (1.8)	6 (1.3)	Percutaneous drainage
Clavien IV/V	IV/V	None	None	None	—
Overall		21 (9)	31 (13.9)	51 (11.2)	—

Ultra-mini PCNL

In total, 223 patients with a mean age of 4.2 years and a male:female ratio of 3:2 underwent UMP (10–14F). The mean stone size was 21 mm (range: 5–48 mm).

The mean initial and final SFR ranged from 76.0% to 91.6% and 85% to 100%, respectively in these studies (Table 2). The definition of SFR varied between studies (<3 or <2 mm) with four studies not providing how they defined SFR in their study. With the exception of one study that used a CT scan, all others used XR in combination with US. The commonest stone location was in the renal pelvis and lower pole calix (Table 5).

Table 5.

Stone Location Reported in the Studies

Author	Upper ureter	Renal pelvis	Renal pelvis and lower calix	Lower calix	Middle calix	Upper calyx	Multiple caliceal stones
m-PCNL
Silay and colleagues¹⁰	0	7	4	7	0	1	0
Bodakçi and colleagues¹¹	0	18	7	0	0	0	0
Dağgülli and colleagues¹²	0	17	6	9	7	1	0
Karatag and colleagues¹³	0	19	7	28	2	0	0
Baş and colleagues¹⁴	0	27	0	8	8	0	2
Dundar and colleagues¹⁵	0	7	0	7	0	0	0
Dede and colleagues¹⁶	0	11	9	0	0	0	4
Caione and colleagues¹⁷	0	1	0	7	0	0	0
UMP
Jackman and colleagues⁶	NR	NR	NR	NR	NR	NR	NR
Bilen and colleagues¹⁸	0	6	3	0	0	0	1
Bilen and colleagues¹⁹	1	8	6	4	0	1	5
Daw and colleagues²⁰	1	16	8	0	0	0	1
Dede and colleagues²¹	0	19	0	6	2	1	11
Liu and colleagues²²	36	26	0	21	9	14	8

In total, 31 (14%) complications were reported across 223 patients included in this review (Table 4). The majority (77%, n = 24) of these were Clavien I and II complications. Clavien I complications (48%, n = 15) included five patients each with fever, hematuria, or urine leak, all of which settled spontaneously. Clavien II complications (29%, n = 9) included five patients who needed blood transfusion, three patients with minor renal pelvic perforation, and one urinary tract infection. Clavien III complications (23%, n = 7) included renal pelvic perforation (n = 3) requiring percutaneous drainage and extravasation requiring PCN (n = 4). Overall the mean drop in Hb was 9.7 g/L with an overall blood transfusion rate of 2.1%. There were no Clavien IV/V complications reported during the review period.

Conversion to other procedures (mini-PCNL, retrograde intrarenal surgery, standard PCNL)

For m-PCNL, conversion to mini-PCNL (M-PCNL) and retrograde intrarenal surgery (RIRS) was required in 2.6% and 0.7% of cases, respectively. Only one case of UMP required conversion to standard PCNL. For both techniques, therefore, the conversion rates were very low.

Use of postoperative drainage (nephrostomy, ureteral catheter, or Double-J Stent)

Around a fifth (21.6%) of patients who underwent m-PCNL had a Double-J stent inserted intraoperatively, whereas the majority (78%) had ureteral catheter placed, which was typically removed after 24–48 hours. Less than 1% of patients had a nephrostomy tube placed.

For UMP, intraoperative Double-J stent placement varied between 11% and 86% in these studies, although there was a decreasing trend over time as the surgeons became more experienced in it. Placement of ureteral catheter and nephrostomy tube was variable and ranged from 0% to 84% and 0% to 100%, respectively.

Discussion

Findings of our study

This is the first systematic review to report on outcomes of miniaturized PCNL (m-PCNL, UMP) in the pediatric population. The outcomes suggest a good SFR for stones between 10 and 20 mm with an overall complication rate of 11.2% (n = 51). While there was a higher incidence of renal colic with m-PCNL, the incidence of hematuria and renal extravasation or renal pelvic perforation was higher with UMP. Our review shows that use of these smaller instruments can deliver a strong safety profile while achieving good stone clearance (Tables 3 and 4).

Advantages of miniaturized PCNL (m-PCNL, UMP)

The advantages of miniaturized PCNL techniques rely on the smaller tract size and dilatation needed for these procedures. There is reduced risk of hemorrhagic complications due to reduced trauma to renal parenchyma from tract dilatation.^5

–8 This is of even higher importance in pediatric populations, where a decrease in Hb carries greater physiological effect and could be fatal. The suitability of miniaturized PCNLs even extends to infants less than 1 year old. Unlike standard PCNL and UMP, use of the m-PCNL enables renal access through a single-step procedure. This facilitates shorter time from insertion to laser lithotripsy. Disintegration (fragmenting or dusting) is achieved under direct vision with a laser leading to more predictable results, in contrast to extracorporeal shockwave lithotripsy (SWL), which does not allow for this.

The success rate for m-PCNL and UMP is high, with only a fraction of cases requiring conversion to larger access methods or standard PCNL. The feasibility of miniaturized techniques has also been demonstrated in cases of anomalous anatomy, including ectopic, solitary, and pelvic kidneys. While the majority of studies reported have been under general anesthesia (GA), it can also be carried out under spinal anesthesia.¹³ Reduced use of irrigation fluid allows for a lower risk of hypothermia, which is a recognized potential complication associated with pediatric PCNL. The learning curve is not considered to be steep for endourologists already practicing standard PCNL. While it was the standard among the studies included in this review to leave a ureteral catheter, this was normally removed within 12 to 24 hours postprocedure. This allows standard Double-J stent placement to be avoided, which can give troublesome symptoms, with a potential need for GA for it removal and the risk of encrustation with forgotten stents.

Disadvantages of miniaturized PCNL

Smaller instruments used for these techniques lack the same visual clarity as opposed to the standard PCNL technique, and even a small amount of bleeding can greatly obscure intraoperative vision. The m-PNCL technique does also not allow for removal of stone fragments and these are therefore left to pass spontaneously. Besides having no stones for biochemistry, this can also lead to readmission with renal colic secondary to ureteral obstruction. Collection of urine postoperatively to sieve fragments is possible, but is not always achievable and many patients may not comply. UMP does however allow for stone retrieval through its access sheath either due to the vortex created by saline flush or removal through a stone basket under vision.²²

Based on available evidence, miniaturized PCNL appears to yield the best outcomes for smaller renal stones, although patient selection is important. Attempting large burden stones could potentially lead to residual fragments causing renal colic or Steinstrasse. Emergency Double-J stent insertion for obstructing fragments comprised 50% of the Grade III complications recorded in this review. Several authors have advocated the potential use of an 8F microsheath to aid with larger stones. This allows passage of a 3F basket catheter to retrieve fragments as well as a larger diameter laser fiber and antegrade Double-J stent insertion if needed.

Silay and colleagues also state that selecting patients is of the utmost importance and Caione and colleagues highlighted that the surgeon performing the procedure should be familiar with the equipment and should be experienced, as errors can have much more serious consequences in children.^10,17

Alternatives for miniaturized PCNL techniques

The current European Association of Urologists (EAU) guidelines for pediatric urology suggest the use of PCNL for staghorn stones and stones >20 mm in the renal pelvis or >10 mm in the lower pole calix.²³ SWL is recommended for stones up to 20 mm or lower pole calix stone <10 mm. However, it does not take into account these new miniaturized PCNL techniques that can be used for smaller stones with minimal morbidity. The role of RIRS as a first line is only recommended for lower ureteral stones.²⁴

The use of SWL in pediatric age group often needs a GA and is associated with repeat sessions to achieve stone clearance. The risks for Steinstrasse and renal colic are not dissimilar to those with miniaturized PCNL. Treatment of lower pole calix stone is also dependent on the infundibulopelvic angle, length, and diameter, with its success also influenced by the stone composition. All these factors can contribute to lower stone clearance with SWL. The use of RIRS is associated with high equipment and treatment costs, with larger stones often needing an access sheath placement, which can be associated with trauma to the ureteral wall in up to 46.5% of cases.²⁵ Additional risks also include ureteral stricture and avulsion. RIRS can also require multiple sessions to achieve stone-free status and ureteral stent is required for comparatively longer periods. Sabnis and colleagues highlighted this in their study comparing RIRS with m-PCNL.²⁶ While similar SFRs and complication rates were reported between the two interventions, patients undergoing RIRS had a greater number of Double-J stent insertions, although the analgesic requirement was higher for m-PCNL.

Limitations and future research

The results of any systematic review are dependent on the parameters and quality of the studies included. While this review is comprehensive in its conduct, some of the studies included did not take into account patients with anatomical or musculoskeletal anomalies and also failed to mention previous procedures patients had undergone.

An ongoing and recognized limitation is the lack of widely accepted definition for “stone free” and reminds the reader the need for caution when comparing study results.²⁷ The heterogeneity of the different study results was such that formal meta-analytic methods were not feasible and therefore analysis was restricted to calculation of pooled mean values only. Given the need to limit pediatric populations' exposure to ionizing radiation, postprocedure imaging is usually limited to plain XR or US. As no randomized trials exist for m-PCNL in pediatric populations, these are needed for direct comparison with RIRS and SWL. Ideally these would be performed in the multicenter setting. Such studies would enable clearer selection criteria for these miniaturized surgical methods.

Our study clearly shows the risk of bleeding and pelvicaliceal rupture or extravasation were associated with the increasing size of tract as in UMP (tract size 10–14F), whereas a lower stent insertion or drainage was associated with a risk of renal colic or emergency stent insertion as shown in m-PCNL (tract size <10F). On comparing m-PCNL and UMP, there was a significantly higher rate of renal colic/fragment obstruction with the m-PCNL (p = 0.0001), but the rates of hematuria and extravasation/pelvicaliceal rupture was higher for UMP (p < 0.001). Still, due to a lack of complete data set and heterogeneous nature of reporting, some results were difficult to compare with other alternate treatment modalities. It is prudent that further randomized studies for management of large pediatric stones is conducted in centers with a high case volume (preferably) offering all available treatment modalities to minimize any potential bias.

Conclusion

Miniaturized PCNL techniques can deliver high SFRs for stones up to 2 cm with a small risk of Clavien I/II complications. The size of tract seems to influence the nature of complications with slightly higher hematuria and renal extravasation with increasing tract size. Future randomized and prospective studies will further delineate the formal position of these techniques in the surgical treatment of pediatric urinary stone disease.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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