The Role of Renal Parenchymal Thickness and Tract Length on Mini-Percutaneous Nephrolithotomy Outcomes in Pediatric Patients

Abstract

Purpose:

To evaluate the effects of renal parenchymal thickness (RPT) and tract length (TL) on the stone-free rate (SFR) and complications in pediatric patients who underwent minimally invasive percutaneous nephrolithotomy (mini-PCNL).

Materials and Methods:

The data of pediatric age group (<18 years) patients who underwent mini-PCNL between 2017 and 2025 in our clinic, which is a tertiary referral center, were retrieved. Eighty patients were included in this study. SFR was determined using low-dose nonenhanced CT in all patients 1 month after procedure. Stone-free status was defined as the complete absence of stones, and the presence of any stone fragment, regardless of size, was defined as residual stone.

Results:

The mean stone diameter was 22.8 mm, and the mean stone burden was 402 mm². Although 46.3% of the stones were located only in the renal pelvis, 32.5% were staghorn. Mean RPT was 13.6 ± 5.0 mm, TL was 33.0 ± 10.5 mm, and RPT/TL ratio was 0.42 ± 0.13. Complications occurred in 27.5% of the patients. No major (grade 4–5) complications were observed in any patient. After mini-PCNL, stone-free status was achieved in 65% of patients. The mean diameter of residual stone was 3.4 ± 5.9 mm. When comparing patients who were stone free and those with residual stones, RPT (p = 0.059), TL (p = 0.315), and RPT/TL ratio (p = 0.563) were similar between groups. When patients with and without complications were compared, no statistically significant difference was found between the two groups in RPT (p = 0.084), TL (p = 0.589), and RPT/TL ratio (p = 0.723).

Conclusions:

Mini-PCNL appears to be an effective and safe surgical technique that can be applied in pediatric patients with kidney stones, regardless of RPT and TL; however, prospective multicenter studies are necessary to confirm our results in a larger number of patients.

Keywords

mini-PCNL percutaneous nephrolithotomy renal parenchymal thickness tract length

Introduction

Pediatric urinary system stone disease is an important health problem. There is an increase in its incidence because of lifestyle, eating habits, and obesity. The incidence of kidney stones in childhood has increased two- to three-fold over the past few decades, with a dramatic increase of 10% per year.¹ Pediatric patients with urinary tract stone disease are considered to be at a high risk of recurrent stone formation. It is important to ensure a stone-free status in patients who may require multiple surgical interventions.² Pediatric urinary tract stones require more challenging treatment because of the small urinary tract size of the patients and the high rate of stone recurrence.³ The primary goal in the surgical treatment of these challenging patients is the maximum stone clearance rate and low perioperative morbidity.⁴

Percutaneous nephrolithotomy (PCNL) is the primary treatment option for pediatric staghorn and renal stones > 2 cm as well as lower pole stones > 1 cm.⁵ The availability of smaller nephroscopes has enabled minimally invasive PCNL (mini-PCNL) in pediatric patients.⁶ Thus, pediatric patients are being treated both safely and effectively with mini-PCNL, a modification of standard PCNL (sPCNL).⁷ The highest relative increase in trends in pediatric endourologic interventions for pediatric urinary tract stone disease was observed with mini-PCNL.⁸ However, even mini-PCNL may cause problems in the pediatric age group because of the relatively smaller size of the patient’s kidneys, small-caliber collecting system, fragile parenchyma, and higher mobility.⁹

The use of preoperative imaging methods and operative parameters may be important for predicting the success and complications of operation.¹⁰ Percutaneous renal access to kidney stones involves the skin, subcutaneous tissue, visceral fat, perirenal space, and renal parenchyma. The length of this tract may play a role in the results of PCNL.¹¹ Since the renal parenchyma is penetrated during access, it may theoretically cause tissue damage and bleeding in patients with thick renal parenchyma, which may affect the stone-free rate (SFR).¹² In addition, there may be a relationship between preoperative imaging parameters and systemic inflammatory response syndrome (SIRS) or urinary leakage (UL) in patients undergoing PCNL.^13,14

Our study aimed to evaluate the effects of renal parenchymal thickness (RPT) and tract length (TL) on SFR and complications in pediatric patients who underwent mini-PCNL.

Patients and Methods

This study was approved by the institutional review board (Decision No: 2025/19-855). Stone disease is endemic in our country. In addition, our hospital is a high-volume center and has surgeons who specialize in pediatric kidney stones. In our study, the data of pediatric age group (<18 years) patients who underwent mini-PCNL between 2017 and 2025 in our clinic, which is a tertiary referral center, were retrieved. Informed consent forms were obtained from the patient’s parents regarding the success and complications of the procedure. Patients over 18 years of age, with a single functioning kidney, with an anatomical urinary tract anomaly, who had a history of open stone procedure, Double-J ureteral stent or nephrostomy tube placement in the ipsilateral kidney, with abnormal renal function, with bleeding diathesis, who had undergone sPCNL, with simultaneous ureteral stones, who underwent multiple access, with a history of renal transplantation or urinary diversion, and with missing data were excluded from the study. All patients were evaluated with thorough medical history, complete blood count, serum biochemistry, coagulation tests, urinalysis, and urine culture. Kidney-ureter-bladder (KUB) radiography and urinary tract ultrasound (USG) were done in all patients as the initial screening procedure. Low-dose nonenhanced CT was performed in all patients scheduled for operation to evaluate the kidney anatomy, stone localization, and the relationship of the colon and surrounding structures with the kidney. Patients with positive preoperative urine cultures were treated with appropriate antibiotics and operated on after obtaining a sterile urine culture. The stone diameter was measured as the longest diameter calculated on CT. The stone burden was estimated using the following formula: longitudinal diameter × orthogonal diameter × π/4(mm²). In the presence of multiple stones, the sum of the longest diameters of all stones was calculated for stone diameter, and the sum of the areas of all stones was calculated for stone burden. RPT was measured as the access line distance from the renal capsule to the apex of the pyramid on CT. TL was defined based on the distance indicators on the needle, which was accessed using an 18-gauge puncture needle during the operation. Postoperative hemoglobin (Hb) and creatinine (Cre) levels were checked 24 hours after operation. Complications were evaluated using the modified Clavien–Dindo grading system. SFR was determined using low-dose CT in all patients 1 month after procedure. Stone-free status was defined as the complete absence of stones, and the presence of any stone fragment, regardless of size, was defined as residual stone.

Operation

All procedures were performed under general anesthesia. As antibiotic prophylaxis, a single dose of cephalosporin was administered intravenously for 30 minutes before operation. A 4F open-ended ureteral catheter was preferably placed in the lithotomy position to fill the collecting system. Then the patient was placed in the prone position. Percutaneous renal puncture was performed with 18-gauge Chiba needle (Boston Scientific Corporation, Natick, MA, USA) under biplanar fluoroscopic guidance. Subcostal access was performed in all patients. Once access was obtained, a 0.035″ guidewire (Sensor^TM Guide Wire, Boston Scientific) was inserted into the collecting system via the needle. The tract was dilated with Amplatz dilators, and then 16F Amplatz sheath was placed. Lithotripsy was performed via a 14F pediatric nephroscope (Karl Storz, Germany) and holmium:yttrium aluminum garnet (Ho:YAG) Laser (Quanta System Cyber Ho 60 W, Samarate, Italy) 550 μm end-firing optical fiber, using power as much as 60 W(1–2 J/15–30 Hz). Fragments were removed using a vacuum cleaner effect and stone forceps. During the operation, fluoroscopic imaging control and endoscopic examination were performed to detect the presence of residual fragments. Since a flexible nephroscope was not available in our hospital, it could not be used to detect the presence of residual stones. A 10F reentry catheter was placed in all patients for postoperative drainage.

Statistical analysis

Continuous variables were expressed as mean ± standard deviation, whereas categorical variables were presented as frequencies and percentages. The normality of continuous variables was assessed using the Shapiro–Wilk test. Comparisons between two independent groups for continuous variables were performed using the Student’s t-test when data were normally distributed, and the Mann–Whitney U test was used for non-normally distributed data. Categorical variables were compared using the chi-square (χ²) test or Fisher’s exact test when appropriate. A p-value of less than 0.05 was considered statistically significant. All analyses were performed using IBM SPSS Statistics version 26.0 (IBM Corp., Armonk, NY, USA).

Results

Considering the exclusion criterion, 80 pediatric patients who underwent mini-PCNL in our clinic between 2017 and 2025 were included in the study. Table 1 presents the demographic data of the patients and the data related to the operation. The mean age of the patients was 9.2 ± 4.1 years. The mean stone diameter was 22.8 ± 9.3 mm, and the mean stone burden was 402 mm². Although 46.3% of the stones were located only in the renal pelvis, 32.5% were staghorn. Mean RPT was 13.6 ± 5.0 mm, TL was 33.0 ± 10.5 mm, and RPT/TL ratio was 0.42 ± 0.13. Complications occurred in 27.5% of the patients. Grade 1, 2, 3a, and 3 b complications occurred in 6.3%, 11.3%, 1.3%, and 8.8%, respectively. No major (grade 4–5) complications were observed in any patient. A Grade 3a complication occurred in one patient because of abdominal tenderness. Grade 3b complications that occurred in seven patients were prolonged UL and associated Double-J stent insertion. After mini-PCNL, stone-free status was achieved in 65% of patients. The mean diameter of residual stone was 3.4 ± 5.9 mm.

Table 1.

The Demographic Data of the Patients and the Data Related to the Operation

	Patients (n = 80)
Age, year, mean ± SD	9.2 ± 4.1
Sex, n (%)
Female	37 (46.3)
Male	41 (53.7)
Ipsilateral renal surgical history, n (%)
Primary	65 (81.2)
Secondary	15 (18.8)
Stone number, mean ± SD	1.7 ± 1.3
Laterality, n (%)
Right	33 (41.3)
Left	47 (58.8)
Stone location, n (%)
Renal pelvis	37 (46.3)
Lower calix	7 (8.8)
Middle calix	1 (1.3)
Upper calix	2 (2.5)
Multiple calices	7 (8.8)
Staghorn	26 (32.5)
Stone diameter, mm, mean ± SD, range	22.8 ± 9.3 (10–45)
Stone burden, mm², mean ± SD	402 ± 383
Stone density, HU, mean ± SD	1004 ± 223
Opacity, n (%)
Radiopaque	68 (85)
Radiolucent	12 (15)
Presence of hydronephrosis, n (%)	50 (62.5)
Hydronephrosis, n (%)
No	30 (37.5)
Grade 1	20 (25)
Grade 2	17 (21.3)
Grade 3	8 (10.0)
Grade 4	5 (6.3)
RPT, mm, mean ± SD	13.6 ± 5.0
TL, mm, mean ± SD	33.0 ± 10.5
RPT/TL ratio	0.42 ± 0.13
Puncture site, n (%)
Lower calix	60 (75)
Middle calix	14 (17.5)
Upper calix	6 (7.5)
Operative time, min, mean ± SD	89 ± 28
Preoperative Hb, g/dL, mean ± SD	12.0 ± 1.1
Postoperative Hb, g/dL, mean ± SD	11.1 ± 1.2
Hb loss, g/dL, mean ± SD	−0.9 ± −0.9
Preoperative Cre, mg/dL, mean ± SD	0.36 ± 0.12
Postoperative Cre, mg/dL, mean ± SD	0.38 ± 0.14
Cre change, mg/dL, mean ± SD	0.01 ± 0.07
Reentry catheter removal time, day, mean ± SD	2.7 ± 2.0
Length of hospital stay, day, mean ± SD	3.2 ± 1.5
Transfusion rate, n (%)	7 (8.8)
Complication rate, n (%)	22 (27.5)
Clavien–Dindo complication grade, n (%)
1	5 (6.3)
2	9 (11.3)
3a	1 (1.3)
3b	7 (8.8)
SFR, n (%)	52 (65)
Diameter of residual stone, mm, mean ± SD	3.4 ± 5.9

Cre = creatinine; Hb = hemoglobin; n = number; RPT = renal parenchymal thickness; SD = standard deviation; SFR = stone-free rate; TL = tract length.

The 28 patients with residual stones and 52 who were stone free are compared in Table 2. Accordingly, the mean stone number of patients with residual stones was 2.2 ± 1.4, and the mean stone number of patients with stone-free status was 1.5 ± 1.2 (p = 0.023). Although the rate of staghorn stones was significantly higher in the residual stone group (60.7%), the rate of isolated renal pelvis stones was significantly higher in the stone-free group (57.7%). Stone diameter and burden were statistically significantly higher in patients with residual stones (p < 0.001). RPT (p = 0.059), TL (p = 0.315), and RPT/TL ratio (p = 0.563) were similar in both groups. Operative time (101 ± 34 minutes vs 83 ± 22 minutes) (p = 0.006) and length of hospital stay (3.9 ± 1.7 days vs 2.8 ± 1.2 days) (p = 0.001) were longer in the group with residual stones. Similarly, reentry removal time was longer in the group with residual stones (3.6 ± 2.9 days vs 2.2 ± 1.0 days) (p = 0.019). There was no significant difference in complication rates between the two groups (p = 0.083).

Table 2.

Comparison of Groups According to the Presence of Residual Stone

	Residual stone (n = 28)	Stone free (n = 52)	p-Value
Age, year, mean ± SD	8.8 ± 3.3	9.4 ± 4.6	0.541
Sex, n (%)
Female	17 (60.7)	20 (38.5)	0.057
Male	11 (39.3)	32 (61.5)
Ipsilateral renal surgical history, n (%)
Primary	20 (71.4)	45 (86.5)	0.099
Secondary	8 (28.6)	7 (13.5)
Stone number, mean ± SD	2.2 ± 1.4	1.5 ± 1.2	0.023
Laterality, n (%)
Right	14 (50)	19 (36.5)	0.243
Left	14 (50)	33 (63.5)
Stone location, n (%)
Renal pelvis	7 (25)	30 (57.7)	0.005
Lower calix	2 (7.1)	5 (9.6)
Middle calix	—	1 (1.9)
Upper calix	—	2 (3.8)
Multiple calices	2 (7.1)	5 (9.6)
Staghorn	17 (60.7)	9 (17.3)
Stone diameter, mm, mean ± SD	28.8 ± 9.7	19.5 ± 7.3	<0.001
Stone burden, mm², mean ± SD	677 ± 487	254 ± 194	<0.001
Stone density, HU, mean ± SD	1011 ± 229	1000 ± 222	0.842
Opacity, n (%)
Radiopaque	25 (89.3)	43 (82.7)	0.431
Radiolucent	3 (10.7)	9 (17.3)
Presence of hydronephrosis, n (%)	18 (64.3)	32 (61.5)	0.809
Hydronephrosis, n (%)
No	10 (35.7)	20 (38.5)
Grade 1	6 (21.4)	14 (26.9)	0.617
Grade 2	5 (17.9)	12 (23.1)
Grade 3	4 (14.3)	4 (7.7)
Grade 4	3 (10.7)	2 (3.8)
RPT, mm, mean ± SD	12.1 ± 4.4	14.3 ± 5.1	0.059
TL, mm, mean ± SD	31.4 ± 10.7	33.9 ± 10.4	0.315
RPT/TL ratio	0.41 ± 0.16	0.43 ± 0.11	0.563
Puncture site, n (%)
Lower calix	20 (71.4)	40 (76.9)	0.226
Middle calix	4 (14.3)	10 (19.2)
Upper calix	4 (14.3)	2 (3.8)
Operative time, min, mean ± SD	101 ± 34	83 ± 22	0.006
Preoperative Hb, g/dL, mean ± SD	12.0 ± 1.1	12.0 ± 1.1	0.918
Postoperative Hb, g/dL, mean ± SD	10.9 ± 1.4	11.2 ± 1.2	0.338
Hb drop, g/dL, mean ± SD	−1.1 ± −0.8	0.7 ± 0.9	0.149
Preoperative Cre, mg/dL, mean ± SD	0.38 ± 0.11	0.35 ± 0.12	0.433
Postoperative Cre, mg/dL, mean ± SD	0.41 ± 0.16	0.36 ± 0.12	0.139
Cre change, mg/dL, mean ± SD	0.027 ± 0.09	0.005 ± 0.069	0.233
Reentry catheter removal time, day, mean ± SD	3.6 ± 2.9	2.2 ± 1.0	0.019
Length of hospital stay, day, mean ± SD	3.9 ± 1.7	2.8 ± 1.2	0.001
Transfusion rate, n (%)	3 (10.7)	4 (7.8)	0.668
Complication rate, n (%)	11 (39.3)	11 (21.2)	0.083
Clavien–Dindo complication grade, n (%)
1	1 (3.6)	4 (7.7)
2	7 (25)	2 (3.8)	0.111
3a	1 (3.6)	—
3b	2 (7.1)	5 (9.6)

Cre = creatinine; Hb = hemoglobin; n = number; RPT = renal parenchymal thickness; SD = standard deviation; TL = tract length.

A comparison of 22 patients with complications and 58 patients without complications is shown in Table 3. Stone number (p = 0.115), stone location (p = 0.346), stone diameter (p = 0.455), and stone burden (p = 0.847) were found to be similar in both groups. No statistically significant difference was found between the two groups in RPT (p = 0.084), TL (p = 0.589), and RPT/TL ratio (p = 0.723). Although Hb drop was more pronounced in patients with complications (1.2 g/dL vs 0.7 g/dL) (p = 0.021), Cre change was similar in both groups (p = 0.886). Although no significant difference was found between the two groups regarding operative time (p = 0.311) and reentry catheter removal time (p = 0.06), the length of hospital stay was statistically significantly longer in patients with complications (4.1 ± 1.8 days vs 2.8 ± 1.2 days) (p = 0.004). Although the SFR was 50% in patients with complications, this rate was 70.7% in patients without complications (p = 0.083). The diameter of the residual stone was similar in both groups (3.7 ± 4.1 mm vs 3.3 ± 6.5 mm) (p = 0.826).

Table 3.

Comparison of Groups According to the Occurrence of Complications

	With complication (n = 22)	Without complication (n = 58)	p-Value
Age, year, mean ± SD	8.6 ± 4.0	9.4 ± 4.2	0.423
Sex, n (%)			0.930
Female	10 (45.5)	27 (46.6)
Male	12 (54.5)	31 (53.4)
Ipsilateral renal surgical history, n (%)			0.575
Primary	17 (77.3)	48 (82.8)
Secondary	5 (22.7)	10 (17.2)
Stone number, mean ± SD	2.1 ± 1.8	1.6 ± 1.1	0.155
Laterality, n (%)			0.328
Right	11 (50)	22 (36.9)
Left	11 (50)	36 (62.1)
Stone location, n (%)			0.346
Renal pelvis	8 (36.4)	29 (50)
Lower calix	1 (4.5)	6 (10.3)
Middle calix	—	1 (1.7)
Upper calix	1 (4.5)	1 (1.7)
Multiple calices	1 (4.5)	6 (10.3)
Staghorn	11 (50)	15 (25.9)
Stone diameter, mm, mean ± SD	24.0 ± 9.7	22.3 ± 9.2	0.455
Stone burden, mm², mean ± SD	388 ± 324	407 ± 406	0.847
Stone density, HU, mean ± SD	929 ± 195	1032 ± 228	0.065
Opacity, n (%)			0.833
Radiopaque	19 (86.4)	49 (84.5)
Radiolucent	3 (13.6)	9 (9)
Presence of hydronephrosis, n (%)			0.365
Hydronephrosis, n (%)	12 (54.5)	38 (65.5)	0.063
No	10 (45.5)	20 (34.5)
Grade 1	7 (31.8)	13 (22.4)
Grade 2	—	17 (29.3)
Grade 3	4 (18.2)	4 (6.9)
Grade 4	1 (4.5)	4 (6.9)
RPT, mm, mean ± SD	12.0 ± 4.2	14.2 ± 5.1	0.084
TL, mm, mean ± SD	32.0 ± 12.3	33.4 ± 9.8	0.589
RPT/TL ratio	0.41 ± 0.18	0.42 ± 0.11	0.723
Puncture site, n (%)			0.670
Lower calix	18 (81.8)	42 (72.4)
Middle calix	3 (13.6)	11 (19)
Upper calix	1 (4.5)	5 (8.6)
Operative time, min, mean ± SD	96 ± 38	87 ± 23	0.311
Preoperative Hb, g/dL, mean ± SD	11.9 ± 1.1	12.0 ± 1.1	0.677
Postoperative Hb, g/dL, mean ± SD	10.6 ± 1.2	11.3 ± 1.2	0.041
Hb drop, g/dL, mean ± SD	−1.2 ± −0.9	−0.7 ± −0.9	0.021
Preoperative Cre, mg/dL, mean ± SD	0.33 ± 0.11	0.37 ± 0.12	0.222
Postoperative Cre, mg/dL, mean ± SD	0.35 ± 0.12	0.39 ± 0.14	0.295
Cre change, mg/dL, mean ± SD	0.01± 0.07	0.01± 0.08	0.886
Reentry catheter removal time, day, mean ± SD	3.8 ± 3.2	2.3 ± 1.2	0.060
Length of hospital stay, day, mean ± SD	4.1 ± 1.8	2.8 ± 1.2	0.004
SFR, n (%)	11 (50)	41 (70.7)	0.083
Diameter of residual stone, mm, mean ± SD	3.7 ± 4.1	3.3 ± 6.5	0.826

Cre = creatinine; Hb = hemoglobin; n = number; RPT = renal parenchymal thickness; SD = standard deviation; SFR = stone-free rate; TL = tract length.

Discussion

In this study, when comparing patients who achieved stone-free status and those with residual stones after pediatric mini-PCNL, no significant difference was found in RPT, TL, and RPT/TL ratio. A similar conclusion was reached when comparing patients who experienced complications with those who did not. Our study is valuable, as it is the first study to evaluate the effects of RPT, TL, and RPT/TL on SFR and complications in pediatric patients undergoing mini-PCNL.

PCNL is recommended as the primary treatment option in children with staghorn calculi, lower caliceal calculi > 10 mm, and renal pelvic calculi > 20 mm.⁵ Compared with adults, developing pediatric kidneys have greater mobility, less operative space, and more fragile renal parenchyma and mucosa. This situation causes great difficulties in the balance between stone clearance and the preservation of kidney function.¹⁵ Concerns about potential kidney damage that PCNL may cause in children, whose organs are still developing, are important reasons for using smaller tract sizes.¹⁶ Although there is no clear definition, PCNL performed using a 14–20 F access sheath in pediatric patients is called mini-PCNL.¹⁷ Although mini-PCNL has been evaluated in terms of efficacy and safety in many studies, neither the definition of stone-free status nor the method of reporting complications is homogeneous among studies. The absence of standardization in defining pre-, peri-, and postoperative aspects highlights the absence of guidelines for the implementation of this surgical procedure.¹⁸

In pediatric patients, complete stone removal is important to preserve renal function and prevent rapid recurrence.¹⁹ Kidney stones have high recurrence rates in the pediatric age group, with approximately 50% of patients experiencing symptomatic recurrence within 3 years.²⁰ In a review by Özden and colleagues, which examined patients who underwent mini-PCNL in the pediatric age group, the SFR was found to be between 75% and 95%.²¹ In a more recent systematic review by Jones and associates, the weighted mean SFR was found to be between 76% and 97.5% in mini-PCNL performed in pediatric patients with a weighted stone diameter of 12 mm.⁷ Mousawi and coworkers evaluated patients in the pediatric age group who underwent mini-PCNL using the Ho:YAG laser for complex stones with a diameter of 11 to 24 mm and found a complete stone clearance rate of 73.2%.²² Çitamak and colleagues defined complete stone clearance as success in the pediatric age group and achieved a success rate of 74.9% in PCNL using a 14–30 F Amplatz renal dilator.²³ In our study, the SFR was found to be lower than that in similar studies in the literature. The main reason for this is the difference in the definition of SFR. Although cutoff values such as 2 mm or 4 mm were frequently used for residual stones in similar studies in the literature, stone-free status was defined as complete clearance of the stone in our study. Considering that recurrence is particularly high in pediatric patients and that even a small stone fragment of any size can become symptomatic and require intervention, we strongly support the definition of complete absence of stone as a stone-free status. In addition, our study evaluated stones with a diameter as large as 45 mm, and multiple calices stones were present at a rate of 8.8% and staghorn stones at a rate of 32.5%. The presence of more complex stones may be another reason for the lower SFR. The use of low-dose CT instead of KUB radiography and USG in the evaluation of stone-free status and the failure to use a flexible nephroscope during operation may also be reasons for the low SFR.

The postoperative complication rate in PCNL varies depending on the complexity of urolithiasis and patient- and procedure-related factors. The aim of mini-PCNL is to reduce complications such as blood loss and hospital stay compared with sPCNL, where a wider access sheath is placed. In addition, a smaller dilation size is thought to cause less damage to the nephrons.²¹ One study emphasized that the complication rate of PCNL in the pediatric age group was approximately 20%, and these rates have increased over the years with the application of PNCL to stones previously considered complex for PCNL.²⁴ In a systematic review of pediatric patients who underwent mini-PCNL, complications occurred in 19% of the patients. The weighted mean transfusion rate reported across studies was 3.3%.⁷ In our study, complications were detected at a rate of 27.5%, and the transfusion rate was 8.8%.

To our knowledge, no study has evaluated the effects of RPT on SFR and complications in pediatric patients who underwent mini-PCNL. Previous studies have mainly examined the relationship between RPT and complications in patients undergoing sPCNL. In some studies investigating the factors affecting hemorrhage in patients undergoing sPCNL, RPT had no effect on the mean Hb drop in univariate analysis.^25,26 However, in the study by Uzun and associates in adult patients who underwent sPCNL, a higher RPT was defined as an independent risk factor for intraoperative bleeding in multivariate logistic regression analysis.²⁷ In their study investigating the factors affecting hemorrhage in patients undergoing sPCNL, Kukreja and coworkers found that patients with RPT > 10 mm had a higher Hb drop than those with RPT < 10 mm (p = 0.05); however, they stated that there was no direct relationship between RPT and hemorrhage.²⁸ Early detection of SIRS is valuable to reduce sepsis and associated mortality rate after PCNL. Although Çetinkaya and colleagues found that patients with low RPT developed SIRS more frequently in univariate analysis in adult patients on whom they performed sPCNL (p = 0.02), RPT was not found to be an independent predictor in multivariate analysis.²⁹ Wei and associates found that a decrease in RPT was an independent risk factor for the development of postoperative SIRS in a multivariate analysis of adult patients who underwent mini-PCNL (p < 0.001).¹³ Apart from hemorrhage and infective complications, UL from the drain site after removal of the postoperative nephrostomy tube is one of the important complications of PCNL. Studies on this subject include only adult patients who underwent sPCNL. Accordingly, various studies have reported that the decrease in RPT in adult patients undergoing sPCNL is associated with the duration of UL, short-term UL (12–48 hours), and prolonged UL (>48 hours).^14,30,31 Similarly, Sahan and coworkers evaluated adult patients to whom they applied sPCNL and found that the decrease in RPT was significant in the multivariate logistic regression analysis of possible factors in predicting UL (p < 0.001).³² Rifaioğlu and associates approached the situation from a different perspective and compared the nephrostomy tube and tubeless groups after PCNL. In their study, they found that the probability of nephrostomy tube placement after operation increased as the RPT decreased. They stated that the tubeless procedure was not suitable for patients with low RPT because these patients were more complicated cases.³³

Tepeler and colleagues colleagues investigated the role of RPT in patients aged 15 to 76 years who underwent sPCNL. In their study, postoperative Hb drop was more pronounced with an increase in RPT (p = 0.01). However, they found no correlation between RPT and operative time, fluoroscopy time, transfusion rate, length of hospital stay, or overall complication rate. In this study, the mean RPT in patients with stone-free status was 17.5 ± 5.4 mm, and the mean RPT in patients with residual stones was 16.1 ± 4.5 mm (p = 0.40).³⁴ Karalar and colleagues emphasized that increased RPT was associated with transfusion rate and Hb drop in adult patients undergoing sPCNL in a univariate analysis (p < 0.01). In the same study, mean RPT was 15.5 ± 5.4 mm in patients who achieved stone-free status and 11.3 ± 5.9 mm in patients with residual stones (p < 0.01). Multivariate analysis showed that an increased RPT was associated with an increased SFR (p < 0.05).¹² In our study, the mean RPT in patients with stone-free status was found to be 14.3 ± 5.1 mm, and the mean RPT in patients with residual stones was found to be 12.1 ± 4.4 mm (p = 0.059). The mean RPT in patients with complications was 12.0 ± 4.2 mm, and the mean RPT in patients without complications was 14.2 ± 5.1 mm (p = 0.084), and again, no statistically significant difference was found.

No study has evaluated the effect of TL on the SFR and complications in pediatric patients undergoing mini-PCNL. To standardize reporting for PCNL, to evaluate and predict SFR and perioperative parameters, stone size (S), tract length (T), obstruction (O), number of involved calices (N), essence (E) (S.T.O.N.E), nephrolithometry was developed for adult patients undergoing sPCNL. In the relevant analysis, no relationship was found between TL and SFR, and TL was not found to be associated with the probability of complications in the multivariate regression model. However, the same study stated that patients with longer TL would experience greater technical difficulties that could negatively affect perioperative outcomes.¹¹ In another scoring system used to predict the results of sPCNL in adult patients, an increased TL was associated with a decreased SFR in the stone score SHA.LIN, which included stone burden (S), hydronephrosis (H), anatomical distribution (A), length of tract (L), indicator of CT (I), and number of involved calices (N).³⁵ Both scoring systems were developed for adult patients, and a 100 mm cutoff is used for TL. Therefore, the fact that all patients in the pediatric age group received the same score from this parameter concludes that both scoring systems are useless in the pediatric age group in terms of the TL parameter. In a study examining the effect of stone-skin distance on surgical outcomes in adult patients undergoing sPCNL, no relationship was found between stone-skin distance and Hb drop, transfusion rate, complication rates, and SFR.³⁶ Studies in the literature have reported that unlike RPT, there is no relationship between TL and UL in adult patients who underwent sPCNL.^30–32 In contrast, Abdelgawad and associates reported that TL significantly predicted short-term UL (12–48 hours) and prolonged UL (>48 hours) in multivariate ordinal regression in adult patients who underwent sPCNL.¹⁴ In our study, the mean TL in patients with residual stones was 31.4 ± 10.7 mm, and the mean TL in stone-free patients was 33.9 ± 10.4 mm (p = 0.315). Similarly, the mean TL was 32.0 ± 12.3 mm in patients with complications, and the mean TL was 33.4 ± 9.8 mm in patients without complications, and no statistical difference was found (p = 0.589).

The limitations of our study are that it was retrospective and single centered; there was no fluoroscopic exposure time, which is of particular importance in the pediatric age group; there were no data on body mass index; there was an absence of data on stone composition (infrared spectrophotometry is not routinely used in the laboratory at our center, most of the stone analyses are performed in private laboratory clinics, and we do not have access to these data); and there was an absence of data on metabolic work-up.

Conclusions

Ethical Approval

The study protocol was approved by the ethics committee of our institution (IRB No: 2025/19-855). The study was performed in accordance with the ethical standards as laid down in the 1964 Declaration of Helsinki and its later amendments.

Informed Consent

Informed consent form was obtained from all patients.

Footnotes

Author Disclosure Statement

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding Information

The authors received no financial support for the research, authorship, and/or publication of this article.

Abbreviations

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