Urolithiasis in the pediatric population has increasing in recent years. Due to the high risk of stone recurrence and the smaller size of the organs involved, the surgical management of kidney stones in pediatric patients remains challenging, particularly for young children. ESWL continues to be the first choice for most pediatric kidney stones. However, its application comes with several limitations, especially for young children, such as the need for general anesthesia, radiation exposure, multiple sessions, and a heightened risk of residual stones[11]. In recent years, with technological advances and the downsizing of instruments, minimally invasive procedures such as PCNL and RIRS have been widely used as substitute for the previous ESWL and open surgeries for pediatric kidney stones[11, 12].
Compared to other minimally invasive treatment methods, PCNL demonstrates superior stone free rates (SFR), albeit with increased invasiveness due to the dilation of the percutaneous tract[13]. With the effort to minimize renal injury, miniaturized PCNL techniques were widespread used which associated with a lower morbidity rate in the pediatric population[14]. In the updated EAU guidelines on pediatric urinary stone disease, PCNL, along with ESWL and RIRS, is the primary treatment for pelvis stones ranging from 10–20 mm[15]. In this study, we compared the effectiveness and safety of two miniaturized PCNL techniques micro-PCNL and ultramini-PCNL characterized by minimal tract diameters (4.85Fr and 11-14Fr) for treatment of 10-20mm kidney stone in preschool-aged children. It showed that both micro-PCNL and ultramini-PCNL were equally effective for treating kidney stones with a low risk of complications.
In our study, micro-PCNL and ultramini-PCNL were both using the specialized optical puncture system called “all-seeing needle”. By using the all-seeing needle technique, percutaneous renal tract is generated under direct vision by ultrasound guided, thereby avoiding radiation exposure. Subsequently, we could directly conduct stone fragmentation without tract dilation referred to as micro-PCNL, or entail dilating the tract to 12-14Fr and perform ultramini-PCNL. The choice we made was mainly dependent on the density, location, and possible component of the stone, as well as the precision achievable in creating the percutaneous renal tract. Despite ultramini-PCNL being used for slightly larger stones (16 ± 4 mm) compared to micro-PCNL (15 ± 4 mm), which was not statistically significant, the procedure times between the two were similar (49 ± 17 mins vs. 54 ± 23 mins, p = 0.351). The ultramini-PCNL procedure, which requires tract dilation, could potentially offer higher lithotripsy efficiency due to the use of a larger laser fiber, allowing stone fragments to be removed spontaneously through the backflow of water rather than merely dusting the stone.
An important parameter for assessing the efficacy of treatment modalities is the stone free rate (SFR). Silay et al. first implemented micro-PCNL in a pediatric cohort of 19 children with a mean age of 7.4 years and an average stone diameter of 14.8 mm, achieving an SFR of 89.5%[16]. Wang et al. treated 27 patients younger than 3 years by micro-PCNL, reporting an SFR of 88.9%[17]. Dede et al. adopted the ultramini-PCNL technique using a 9.5F pediatric cystoscope and a 12F access sheath, noting an average age of 5.8 years, a mean stone diameter of 20.4 mm, and achieving an 87.1% clearance rate[10]. In our current study, the overall SFR in the 64 patients was 85.9%, which is similar to the literature. Notably, the SFR for micro-PCNL (84.8%) and ultramini-PCNL (87.1%) were statistically comparable, suggesting that the efficacy of micro-PCNL is not compromised by the reduced tract size. Both micro-PCNL and ultramini-PCNL demonstrate substantial effectiveness in treating moderate-sized kidney stones, validating their utility in pediatric urological practice.
The superiority of micro-PCNL and ultramini-PCNL is attributed to their smaller tract size and the reduced need for dilatation in these procedures. This holds even greater significance in pediatric populations, where a decrease in trauma to the renal parenchyma from tract dilatation contributes to a reduced risk of hemorrhagic complications, potentially averting fatal outcomes[18, 19]. In this study, the mean hemoglobin drop was 0.3 ± 0.4 g/dL and 0.5 ± 0.5 g/dL, respectively, with no need for blood transfusion in any of the patients. Additionally, no severe hematuria was observed after surgery in either group. According to our center's experience, severe bleeding is rare during pediatric micro-PCNL and ultramini-PCNL procedures. In cases of noticeable bleeding, we typically employ simultaneous manual compression of the abdomen and lumbar region to achieve hemostasis. This is complemented by bladder irrigation to prevent the formation of blood clots. The effectiveness of this approach is largely due to the thinner abdominal walls in preschool children, which facilitate effective compression and subsequent hemostasis.
Tubeless procedures have been demonstrated to be safe and effective in children. It could decrease postoperative analgesia requirement and shorten duration of hospitalization than conventional nephrostomy tube placement after PCNL[20, 21]. If the procedure was uncomplicated without obvious bleeding and there is no preoperative urinary infection, a totally or partial tubeless procedure would be performed in the micro-PCNL group and ultramini-PCNL group. In our study, there were 12 patients in micro-PCNL group who only with a ureteric catheter left overnight. And in ultramini-PCNL group 8 patients underwent partial tubeless procedure only with double-J stent and 10 patients with nephrostomy tubes removed ureteric catheter the day after operation. However, one patient in micro-PCNL group experienced renal colic after ureteric catheter removed because of steinstrasse and required double J stent insertion. The small diameter of the ureter and the limited capacity of micro-PCNL for fragment extraction could be contributing factors. Micro-PCNL technique is based on the principle of ‘‘break and leave’’ without fragments extraction. Stone fragments generated during lithotripsy might flush out into ureter leading to obstruction. Hence, comprehensive consideration is needed on how to appropriately select cases for tubeless procedures in younger pediatric patients.
Another concern for urologists is the high pressure and poor vision during the micro-PCNL lithotripsy procedure within a closed intrarenal system[7]. Retrieving stones for chemical analysis in the micro-PCNL procedure, crucial for pediatric stone management, is also challenging. The ultramini-PCNL technique, utilizing a 12Fr or 14Fr sheath, addresses these concerns by facilitating the movement of irrigation fluid and maintaining low pressure. Additionally, it allows for the retrieval of stone samples through backflow via the sheath, allowing for stone analysis in pediatric cases.
There were no serious complications in our study. One patient in micro-PCNL group showed persistent renal colic and steinstrasse requiring stent insertion (Clavien grade IIIb). Hematuria was observed in 1 patient in micro-PCNL group and 2 in ultramini-PCNL group, none of whom required additional treatment. Fever requiring intravenous medical treatment was also observed in 2 patients in micro-PCNL group and 3 patients in ultramini-PCNL group. No severe hematuria was observed in this study.
Compared to other PCNL techniques, micro-PCNL have some different technical details for pediatric patients that could to be discussed. Creating the percutaneous renal tract in pediatric patients, especially infants, can pose significant challenges, even for experienced endourologists. The preferred site for puncture to access the pelvicalyceal system in PCNL is the fornix of the papilla[22]. However, in certain cases, challenges may still arise due to rib interference or slight hydronephrosis of the target calyx, making it difficult to achieve perfect puncture through the calyx or papilla. Given the absence of the need for tract dilation in micro-PCNL, the completion of lithotripsy carries a low risk of bleeding by non-papillary renal puncture as long as visibility remains clear. For ultramini-PCNL technique, it demands higher precision in puncture to minimize the risk of bleeding. Tract dilation can only proceed once it is confirmed that the puncture pathway is both accurate and secure.
There are some limitations in this study. Firstly, it is a retrospective study not randomized study, which introduces the possibility of selection bias. Secondly, the stone free status was assessed with KUB and ultrasound not computed tomography scan with the concerns of the radiation exposure. Lastly, the sample sizes for each group were relatively small, necessitating larger prospective studies to confirm our findings.