Congenital Ureteropelvic Junction Obstruction (UPJO) is a common ureteral anomaly, occurring in approximately 1 in 750–1,500 newborns (1). UPJO impedes normal urinary excretion, leading to upper urinary tract dilatation and renal functional impairment, which predispose to calculus formation (2). Pyeloplasty is the standard treatment for UPJO, with a success rate of nearly 90% (3). Nonetheless, even after pyeloplasty, kidney stones may still develop, associated with renal dysfunction, metabolic disorders, relative stenosis at the junction, and other factors (2, 4).

Compared with percutaneous nephrolithotomy (PCNL) or extracorporeal shock wave lithotripsy (ESWL), retrograde intrarenal surgery (RIRS) or flexible ureteroscopic lithotripsy (FURS) has emerged as the preferred treatment for upper urinary tract stones smaller than 20 mm. This approach uses a flexible ureteroscope, laser lithotripsy equipment, and a ureteral access sheath (UAS). RIRS is favored due to its high stone-free rate (SFR), low complication rate, and minimally invasive nature. Additionally, it avoids the repeated disconnection of the pelviureteric junction (5–7). A novel type of UAS, the tip-flexible vacuum-assisted ureteral access sheath (FV-UAS), features excellent flexibility and deformability at its tip, allowing it to passively bend in sync with the FURS (8). Wei Zhu et al. (8) demonstrated that FV-UAS provides significant safety and efficacy in adults. This article mainly demonstrates RIRS combined with FV-UAS in the treatment of urinary lithiasis after pyeloplasty for UPJO in a child.

Intraoperatively, not only were the stones in the inferior calyx of the left kidney located, but also submucosal stones aggregation near the middle calyx was identified (Figure 4), showing a history of stones formation and a potential risk of metabolic abnormalities in the child. Laser lithotripsy was utilized to fragment the stones, and the majority of the stone fragments were removed (Supplementary Video S1). Postoperative stone analysis revealed a mixed composition (60% protein, 40% anhydrous uric acid).

Upon postoperative examination with the FURS, the anastomosis was well and there was no obvious damage to the ureter. The US revealed no significant abnormal echoes in the kidneys, ureters, or bladder, no obvious dilation of the bilateral ureters and no progression of dilatation of the left upper urinary tract two days after surgery. The child was prophylactically administered Cefuroxime Sodium 1.5 g bid within 48 h postoperatively. The patient remained asymptomatic without fever, hematuria, or worsening dilation and was discharged in stable condition.

For patients with UPJO accompanied by stones, open or minimally invasive pyeloplasty is the preferred treatment, which can achieve a high SFR while relieving obstruction (9–11). However, given that the child has undergone pyeloplasty and the anastomosis at the pyeloureteric junction is well, repeated damage to the pyeloureteric junction may lead to secondary postoperative stenosis. Moreover, based on the European Association of Urology guidelines (12), for renal stones less than 20 mm in the lower calyx or non-lower calyx, RIRS is considered the first-line treatment option. Moreover, potential indications of RIRS include anatomic abnormalities of the urinary system, multiple kidney stones, bleeding disorders, ancillary procedures after PCNL, obesity etc. There is no specific contraindication for RIRS, except an untreated urinary tract infection and other anesthesia contraindications (13). Therefore, RIRS is selected. FURS and FV-UAS enter the kidney through the urethra, bladder, and ureter, which is a non-invasive operation and avoids repeated disconnection of the pyeloureteric junction. In addition, compared with other lithotripsy surgeries, De Shuba et al. (14) indicated that although the SFR of RIRS is lower than that of PCNL, the probability of complications such as bleeding, infection, and fever and hospital stays after PCNL are significantly higher than those of RIRS. For stones less than 2 cm, Arif Demirbas et al. (15) thought the SFR of RIRS is higher than that of minimally PCNL. Moreover, ESWL may lead to stone excretion difficulty, causing stone accumulation at the stenosis and secondary obstruction.

During RIRS, the UAS directly establishes renal access and is connected to negative pressure suction. After laser lithotripsy, stone fragments can be expelled through the gap between the UAS and the FURS along with the irrigation fluid, or with the irrigation fluid after withdrawing the FURS. However, the traditional rigid UAS has poor flexibility and bending capabilities, and is generally placed at the pyeloureteric junction, resulting in poor regulation of intrarenal pressure. During RIRS, increased intrarenal pressure may cause urine reflux and absorption, leading to severe infections. The FV-UAS is a novel type of UAS featuring excellent flexibility and deformability at its tip. Similarly, it can be connected to a negative pressure suction device. The FV-UAS can pass the pyeloureteric junction alongside the FURS, and under its guidance, the FV-UAS can approach the stone as closely as possible, accurately sucking up stone fragments while maintaining a low intrarenal pressure through negative pressure suction. This reduces the risk of urine reflux (8, 16).

Many clinical studies have proved the effectiveness of RIRS combined with FV-UAS. Yujun Chen et al. (17) found that FV-UAS can achieve complete stone clearance without the need to use stone baskets to reduce costs, and FV-UAS can maintain a low intrarenal pressure under the condition of high-flow rate irrigation fluid, which can reduce the occurrence of complications while ensuring a good surgical field of vision and high clearance rate. As for traditional UAS, clinical researches (18) indicate that the effectiveness of RIRS with traditional rigid UAS is not ideal, with SFR ranging from 50% to 90% in adult patients during the initial surgery, and 50% to 92% in pediatric patients. Ito et al. (19) thought that dilation of the renal pelvis and renal calyces could increase the difficulty of lithotripsy and stone basket removal, and the possibility of residual stones after surgery. Baiyang Song et al. (20) also demonstrated through in vitro experiments that severe upper urinary tract dilatation significantly impairs stone excretion. Moreover, when dealing with the inferior caliceal stones, the bending degree of FURS is so limited within the traditional rigid UAS, resulting in a low SFR of RIRS that Unsal et al. (21) once believed that PCNL should be the first choice for the treatment of lower caliceal stones larger than 10 mm. However, Deheng Cui et al. (22) proved that FV-UAS has significant advantages in SFR by virtue of its bendable head, and Gaoyuanzhi Yue et al. (23) used FV-UAS to treat an 11 mm stone in the left inferior renal calyx of a female patient, achieving the 100% SFR without the assistance of a stone basket and without any complications occurring. In addition, Wei Zhu et al. (8) also pointed out that the process of placing FV-UAS is smoother with less resistance, causing less damage to the ureter compared to traditional UAS. Hui Liang et al. (24) conducted a retrospective analysis of 244 stone patients treated with RIRS combined with FV-UAS, and only 2 cases developed fever symptoms. Therefore, RIRS combined with FV-UAS can achieve a higher SFR and lower complication rate, but it should be noted that FV-UAS may still cause fluctuations and sudden increases in intrarenal pressure, leading to serious complications such as renal abscess (25), so regulating intrarenal pressure is an important factor in reducing postoperative complications of RIRS.

In this study, the child exhibited significant deformation and tortuosity of the renal pelvis and calyces, making it more challenging to explore as many angles as possible. The RIRS combined with FV-UAS ensures a good surgical field of vision with lower intrarenal pressure. This approach allows for the detection of hidden stones in the long and narrow, curved calyces. Moreover, faced with deformed and narrowed calyces, if a traditional rigid UAS were used, relying solely on irrigation fluid to flush the stones into the renal pelvis and ureter would increase the likelihood of stone residue due to generating vortexes. In contrast, the targeted suction of FV-UAS avoids this risk, achieving a higher SFR. Furthermore, the smoother and softer FV-UAS can easily pass through narrow segments of the ureter and operate in the broader renal pelvis, reducing the risk of damage to the ureteral wall and avoiding secondary obstruction at the anastomosis site post-lithotripsy.

In summary, the FV-UAS is a crucial auxiliary tool and RIRS combined with FV-UAS can ensure a high SFR and reduce complications in a non-invasive manner, and can also be used in cases of ureteral stenosis. However, maintaining low intrarenal pressure is essential. Therefore, for children with secondary urinary stones after pyeloplasty for congenital UPJO, RIRS combined with FV-UAS is an effective, safe, and non-invasive surgical approach.