Mini PCNL and single-use flexible ureteroscopy show comparable stone-free rates in children with 10–30 mm kidney stones

Kidney stones are not just an adult problem. Children who form stones face a higher lifetime risk of recurrence, and their smaller, more delicate urinary tracts make every surgical decision more consequential. A new prospective randomized trial published in the African Journal of Urology has now compared two minimally invasive techniques head to head in children with renal stones measuring 10 to 30 millimeters, and the results suggest that neither approach is a clear winner. Instead, each offers a distinct set of trade-offs that surgeons and families will need to weigh together.

The study, conducted between July 2021 and August 2024 at a university hospital, enrolled 90 children under 18 years old and randomized them equally into two groups. Group I, with 46 patients, underwent miniaturized percutaneous nephrolithotomy, often called mini PCNL, a technique in which surgeons create a small tract through the skin into the kidney to reach and remove stones. Group II, with 44 patients, underwent retrograde intrarenal surgery using a single-use flexible ureteroscope, a thin instrument threaded through the natural urinary passage up into the kidney, avoiding any puncture through the flank. The trial was registered at clinicaltrials.gov and approved by the institutional ethics committee, with written informed consent obtained from parents or legal guardians.

To be eligible, children needed a single calyceal or renal pelvic stone of 10 to 20 millimeters, a single renal stone of 20 to 30 millimeters, or multiple stones whose combined maximum diameters totaled 10 to 30 millimeters as measured on non-contrast computed tomography. Patients with uncorrected coagulopathy, renal or ureteral malformations, significant anatomical obstruction requiring separate intervention, or associated metabolic disorders were excluded. Stone burden was deliberately defined as the sum of the maximum diameters of all stones to keep the comparison consistent for children with multiple stones.

Randomization was performed with an online randomization program using block sizes of four, with each patient’s allocation sealed in an opaque envelope until just before surgery. Because the two techniques look nothing alike, the study was necessarily open label, but it remained single blinded: the patients and their families did not know which procedure had been planned, and the radiological assessor who judged outcomes was blinded to treatment allocation. All operations were performed by two senior pediatric endourologists with more than five years of experience, following a standardized institutional protocol.

The technical details of each approach differed substantially. In the mini PCNL group, surgeons obtained percutaneous access under fluoroscopic guidance, dilated the tract in a stepwise fashion up to 15 French using Alken metal dilators, and used a 12 French mini-nephroscope with a holmium laser to fragment stones. Fragments were retrieved with forceps and the vacuum-assisted evacuation effect of the mini-PCNL system, and a 10 French nephrostomy tube was placed for drainage at the end of the procedure. In the flexible ureteroscopy group, a semi-rigid ureteroscope was first used to evaluate the ureter and place a guidewire, and then a single-use flexible ureterorenoscope was advanced into the renal pelvis under combined fluoroscopic and endoscopic guidance. Stones were dusted with a holmium laser through a 200 micron fiber, with basket retrieval only when fragments were needed for analysis.

The primary outcome was complications graded by the Clavien-Dindo system, with operative time, fluoroscopy time, postoperative stenting, stone clearance and hospital stay as secondary outcomes. Stone-free status was defined as the complete absence of residual fragments or only clinically insignificant fragments of 4 millimeters or less, assessed on non-contrast computed tomography four weeks after surgery. The sample size was calculated to detect a difference in total Clavien complication rates based on prior published figures, with 90 percent power, and twelve additional cases were added to cover potential dropout.

When the results came in, the two groups proved remarkably similar where it mattered most. The stone-free rate was 91.3 percent in the mini PCNL group and 88.6 percent in the flexible ureteroscopy group, a difference that was not statistically significant. Complication profiles were also comparable. In the mini PCNL group, renal pelvis perforation occurred in two patients and intraoperative bleeding in four, while no such events were recorded in the ureteroscopy group. Postoperatively, fever appeared in three mini PCNL patients and four ureteroscopy patients, hematuria in six and two respectively, and one mini PCNL patient required a blood transfusion. All complications in both groups fell into the mildest Clavien-Dindo categories, grade I or grade II, and the differences between groups were not statistically significant.

The meaningful differences emerged in efficiency, radiation and recovery. Mean operative time was shorter for mini PCNL at 78.8 minutes compared with 94.2 minutes for flexible ureteroscopy, a difference that reached statistical significance. Postoperative stenting told a similar story: double-J stents were inserted in 60.9 percent of mini PCNL patients versus 86.4 percent of ureteroscopy patients. On the other side of the ledger, fluoroscopy time, radiation dose and dose-area product were all significantly higher in the mini PCNL group, reflecting the fluoroscopy-guided percutaneous access that the technique requires. Hospital stay was also significantly longer after mini PCNL, averaging 3.1 days compared with 1.6 days after flexible ureteroscopy.

Some of these patterns have explanations rooted in the study’s own protocols. The authors note that the insertion of a nephrostomy tube for drainage is a main reason for the longer hospital stay in the PCNL group, although in practice most tubes were removed on the second postoperative day and did not themselves prolong admission. They also acknowledge that ultrasound-guided percutaneous access could reduce radiation exposure compared with the fluoroscopy-guided approach used here, but their center’s expertise with renal ultrasonography in pediatric patients was limited during the study period. Meanwhile, in the ureteroscopy group, 52.2 percent of children required pre-stenting to dilate a tight ureter before the definitive procedure, an extra anesthetic exposure and procedural step that the authors flag as a real consideration in children, where repeated anesthesia is a concern, and one that may have contributed to the higher postoperative stenting rates in that arm.

The authors position their trial as the first prospective randomized study to specifically evaluate the safety and efficacy of single-use flexible ureteroscopy against mini PCNL in children with 10 to 30 millimeter renal stones, a gap they note given the limited number of direct comparisons in pediatric populations. They are candid about the limitations: the stone burden was heterogeneous, ranging from single small stones to multiple stones totaling up to 30 millimeters; no formal stone complexity scoring system such as the Guy’s Stone Score or RENAL score was prospectively applied; randomization was not stratified, so residual confounding cannot be excluded; and procedural variability in nephrostomy use, stenting strategies and dilation techniques may have influenced perioperative outcomes such as hospital stay. They call for future studies with subgroup analyses by stone size and standardized reporting of auxiliary procedures. Within those constraints, the trial’s message is measured and practical: for children with renal stones in this size range, mini PCNL and single-use flexible ureteroscopy deliver comparable stone clearance and mild complication profiles, and the choice between them hinges less on efficacy than on which trade-offs, shorter operative time and less stenting on one side, less radiation and a shorter hospital stay on the other, matter most for the individual child.

Subject of Research: A randomized comparison of mini percutaneous nephrolithotomy and single-use flexible ureteroscopy for treating 10–30 mm renal stones in children.

Article Title: Prospective randomized comparison of mini percutaneous nephrolithotomy and retrograde intrarenal surgery for pediatric renal stones (10–30 mm)

Article References: Eldeeb, M., Nagla, S., El Gamal, O., El Gamal, S., Omar, M. A., & Elmaadawy, M. (2026). Prospective randomized comparison of mini percutaneous nephrolithotomy and retrograde intrarenal surgery for pediatric renal stones (10–30 mm). African Journal of Urology, 32(1), Article 78. https://doi.org/10.1186/s12301-026-00625-y

Image Credits: AI Generated

DOI: 10.1186/s12301-026-00625-y

Keywords: pediatric urology, kidney stones, mini PCNL, flexible ureteroscopy, randomized trial, stone-free rate, Clavien-Dindo complications, fluoroscopy time, DJ stenting, hospital stay, operative time, single-use scope