Successful Treatment with a 6.3-Fr Disposable Digital Flexible Ureteroscope and Holmium Laser Lithotripsy in a 50-Year-Old Man with Large Bilateral Ureteral Stones and Hydronephrosis

Introduction

Ureteral stones are a common urological disorder, with an estimated global incidence ranging from 5% to 15%, and recurrence rates approaching 50% within 5 years [1]. Risk factors include dehydration, dietary habits, such as high salt and animal protein intake, obesity, metabolic abnormalities, such as hypercalciuria and hyperuricosuria, and genetic predisposition [2]. Diagnosis primarily relies on imaging, with non-contrast-enhanced computed tomography (CT) being the criterion standard due to its high sensitivity and specificity. Other modalities include ultrasonography and intravenous urography, although these are less accurate for detecting small or distal stones [3].

Impacted ureteral stones refer to stones that remain in the ureter for an extended period, leading to ureteral edema and fibrosis, and even causing complications such as sepsis. The risks include urinary tract infections, ureteral stenosis, kidney function damage, and in severe cases, renal failure [4]. Treatment methods for impacted ureteral stones include extracorporeal shock wave lithotripsy, flexible ureteroscopy (FURS), percutaneous nephrolithotomy (PCNL), and laparoscopic ureterolithotomy [5]. Among these, holmium: YAG laser lithotripsy, performed via FURS, is considered the criterion standard for endoscopic stone fragmentation due to its safety, efficacy, and precision in breaking down stones of various compositions and sizes [6]. The European Association of Urology guidelines recommend the preferential use of FURS or PCNL for ureteral stones larger than 15 mm, as they are less invasive and have higher stone clearance rates [3].

Disposable digital flexible ureteroscopes have gradually replaced reusable ureteroscopes because they not only solve issues such as high maintenance costs and complex sterilization processes but also provide similar or even better outcomes in terms of technical characteristics such as optical resolution, deflection, and irrigation flow rate [7,8].

Studies have shown that when the intrapelvic pressure exceeds 40 cm H O, it can lead to serious complications; therefore, maintaining low intrapelvic pressure is crucial in the management of complex stones [9]. The ratio of the outer diameter of the flexible ureteroscope to the inner diameter of the ureteral access sheath (UAS) – referred to as the ratio of endoscope to sheath diameter (RESD) – is a key factor in determining renal pelvic pressure; a smaller RESD helps reduce this pressure. A thinner ureteroscope lowers the RESD and reduces the risk of ureteral stricture caused by intraoperative ureteral injury. We used the smallest new 6.3-Fr single-use digital flexible ureteroscope available on the market. Its working channel is the same as that of traditional 7.5-Fr or larger ureteroscopes [10,11]. Compared with the commonly used 7.5-Fr ureteroscope, the 6.3-Fr flexible ureteroscope is thinner, which significantly reduces mechanical trauma to the ureter and lowers the risk of postoperative ureteral stricture, inflammation, and discomfort [10].

Geavlete et al reported that the 6.3-Fr single-use ureteroscope achieved better outcomes than did the 7.5-Fr device for renal stones smaller than 2 cm [12]. However, its utility in managing complex upper urinary tract stones, particularly large bilateral impacted ureteral stones, remains unexplored. This report presents a successful case of a 50-year-old man with large bilateral impacted ureteral stones and hydronephrosis treated with a 6.3-Fr disposable digital flexible ureteroscope and holmium laser lithotripsy, further evaluating the device’s advantages and limitations in complex ureteral stone management.

Case Report

A 50-year-old man was found to have bilateral upper ureteral stones and bilateral hydronephrosis during a routine check-up at a local hospital. Ultrasound examination revealed these findings; however, the patient had no prior history of back pain or gross hematuria. Physical examination showed no significant renal percussion pain.

After transfer to our hospital, further examination revealed a hepatitis B surface antigen level greater than 250 IU/mL (reference range <0.05 IU/mL). Urinalysis results showed leukocytes ranging from 10 to 50/μL (reference range <3/μL), and urine culture results were negative. Liver function, renal function, C-reactive protein, and procalcitonin levels were all within the reference range. The patient had a history of hypertension, duodenal fatty ulcers, and gastric ulcers, which were all treated appropriately.

CT scans revealed a stone in the right upper ureter (22×10×10 mm, 1249 Hounsfield units [HU]), with severe right renal hydronephrosis. The left side had an upper ureteral stone (11×10×8 mm, 1051 HU), a lower calyceal stone in the left renal pelvis (9×9×6 mm, 1005 HU), and moderate left renal hydronephrosis (Figure 1).

The patient received a primary diagnosis of bilateral ureteral stones, bilateral hydronephrosis, and urinary tract infection. After receiving anti-infection treatment, the patient underwent bilateral FURS for stone removal. The procedure began with general anesthesia, and the patient was placed in the lithotomy position. A semi-rigid 6/7.5-Fr ureteroscope was inserted through the urethra. The bladder appeared normal, and after locating the right ureteral orifice, a 0.035-inch guidewire (150 cm; NiCore Nitinol, Bard Inc, GA, USA) was inserted into the right ureter. A 10/12-Fr flexible vacuum-assisted ureteral access sheath (FAV-UAS; Shenzhen Kangyibo Technology Development Co, Ltd, Shenzhen, China) was successfully placed under the guidewire guidance. A 6.3-Fr disposable digital flexible ureteroscope (HU30M HugeMed) was inserted through the FAV-UAS, which was adjusted beneath the stone with the ureteroscope’s guidance. During the procedure, large amounts of polyps were observed surrounding the impacted right upper ureteral stone (Figure 2). A 200-um holmium laser fiber (Lumenis Puls 100H Holmium Laser System, Boston Scientific, CA, USA) was used to fragment the stone, and all fragments were aspirated using the FAV-UAS, which was connected to the central vacuum system. A 5-Fr Marflow D-J stent (APR Medtech, Oxfordshire, UK) was left in place along the guidewire.

The same procedure was followed on the left side. The 10/12-Fr FAV-UAS was inserted into the left upper ureter, where polyps were also observed surrounding the impacted stone. After laser fragmentation of the left upper ureteral stone and left renal stone, all fragments were suctioned out. Another 5-Fr Marflow D-J stent was left in place along the guidewire. The entire procedure was successful, with no intraoperative complications, and the operation time was 106 min.

Postoperative CT on the first day confirmed that all stones had been successfully removed and bilateral hydronephrosis was reduced (Figure 3). Follow-up ultrasound at 1 month and 3 months showed significant reduction in bilateral hydronephrosis. The patient recovered well without any postoperative complications. Postoperative stone composition analysis revealed that the stones were made of calcium oxalate monohydrate and calcium oxalate dihydrate.

Discussion

This case report demonstrates the clinical application of the 6.3-Fr disposable digital flexible ureteroscope in treating large impacted bilateral ureteral stones. From this case, several key observations can be made that highlight the advantages of using a thinner ureteroscope in the management of impacted stones. First, it provides insight into how advancements in ureteroscopic technology, such as the 6.3-Fr flexible ureteroscope, can improve surgical outcomes in patients with challenging ureteral stones, particularly in minimizing complications such as ureteral injury, postoperative infection, and stricture formation.

When ureteral stones remain in the same position for an extended period, they can cause chronic inflammation of the surrounding ureteral mucosa, leading to ureteral edema, polyp formation, and stone impaction. Such stones are referred to as impacted stones. Compared with non-impacted ureteral stones, impacted ureteral stones have a lower stone-free rate and higher complication rates postoperatively, and they remain a challenge for urologists. Therefore, it is crucial to predict stone impaction preoperatively and implement safe and effective treatment [13,14].

Ureteral wall thickness (UWT) has become a commonly used indicator for predicting ureteral stone impaction. Studies have shown that high UWT is associated not only with stone impaction but also with ureteral edema and polyp formation. Research indicates that the optimal cutoff value for UWT is 3.49 mm. High UWT leads to longer surgical times and a lower stone-free rate [15,16]. In the present case, the patient’s UWT on both sides was 4.2 mm (Figure 4). During the procedure, a large number of polyps were found around the stone, confirming that UWT is an effective predictor for ureteral stone impaction.

With advancements in imaging technology, the CT value of stones measured by non–contrast-enhanced computed tomography can predict stone composition and assess stone fragility. Stones with a CT value greater than 1000 HU on bone window settings respond poorly to shockwave lithotripsy [17]. Currently, the treatment methods for impacted large ureteral stones include FURS, PCNL, antegrade ureteroscopy, and laparoscopic ureterolithotomy [5]. The incidence of stricture formation after ureteral stone surgery ranges from 0.5% to 5%, and in patients with impacted ureteral stones, it can reach up to 24% [18]. The European Association of Urology reports that the incidence of urinary tract infections after stone surgery is approximately 1% to 3.7%, while the incidence of postoperative fever is 4.4%, and the incidence of urosepsis is 0.7% [3]. Some studies have reported that, compared with standard ureteroscopy, FURS resulted in lower stone migration rates during surgery, shorter operation times, lower postoperative urinary tract infection rates, and fewer cases requiring a second procedure [19]. Studies have shown that there is no statistically significant difference in stone clearance rates between PCNL and FURS. However, the decrease in hemoglobin levels in a PCNL group was found to be significantly greater than in the FURS group, and the postoperative hospital stay was noticeably longer [20]. With the improvements in retrograde intrarenal surgery-related equipment and techniques, the use of flexible ureteroscopes combined with a FVA-UAS for laser lithotripsy has gradually become accepted as a first-line treatment for impacted ureteral stones [21].

In our case, a novel 6.3-Fr disposable digital flexible ureteroscope was successfully used to treat a patient with large impacted bilateral ureteral stones. The flexible ureteroscope we used is currently the thinnest commercially available disposable ureteroscope (Figure 5). It has a perimeter of 6.3 Fr, but its working channel is the same as that of traditional 7.5-Fr or thicker ureteroscopes, measuring 3.6 Fr. This flexible ureteroscope also features a 285° bidirectional deflection function, which can be adjusted via a knob, allowing the scope to rotate 60° in clockwise and counterclockwise directions. As a result, the visual and operational performance of this ureteroscope is comparable to that of thicker ureteroscopes. Our previous cases have shown that the 6.3-Fr flexible ureteroscope demonstrates significant clinical advantages in the treatment of lower calyx stones in patients undergoing anticoagulant therapy [10]. These advantages include reduced risk of ureteral injury and bleeding, lower postoperative infection rates, and improved single-session success rates [10].

Some studies have reported that intrapelvic pressure rising above 40 cmH2O can lead to renal pelvic–renal sinus reflux, renal pelvic–venous reflux, and renal pelvic-lymphatic reflux, which can subsequently cause complications such as pyelonephritis, urosepsis, subcapsular renal hematoma, and perirenal hematoma. Maintaining lower renal pelvic pressure is particularly important during the management of complex stones [9]. The ratio of outer diameter of flexible ureteroscope and inner diameter of UASs (RESD) is a key factor in determining intrapelvic pressure. Research has shown that when RESD is greater than or equal to 0.87, even with an irrigation pressure of only 250 cmH2O, the renal pelvic pressure still exceeds 40 cmH2O, while when RESD is less than or equal to 0.75, the renal pelvic pressure remains below 13 cmH2O even with an irrigation pressure of up to 500 cmH2O. In vitro studies suggest that the RESD should ideally be less than 0.85 [22]. Furthermore, a lower RESD value not only significantly reduces renal pelvic pressure but also maintains a higher perfusion flow rate, thereby reducing laser thermal damage and ensuring a clear surgical field [23]. The 6.3-Fr ureteroscope provides a better sheath-to-scope ratio, with an RESD of 0.525 when paired with a 12/14-Fr UAS, and an RESD of 0.63 when paired with a 10-Fr UAS (Figure 6). A smaller RESD optimizes irrigation flow and helps maintain lower renal intrapelvic pressure during the procedure. This design characteristic significantly reduces the risk of renal pelvic venous reflux and bacterial bloodstream entry, thereby lowering the incidence of postoperative systemic infections. Especially in the treatment of impacted large ureteral stones, an environment of lower intrapelvic pressure is crucial in reducing the occurrence of systemic infections and urosepsis. In the present case, the patient did not develop any fever or infection-related symptoms postoperatively, further supporting that a thinner ureteroscope helps reduce renal pelvic fluid reflux, alleviate intrapelvic pressure, and decrease the risk of infection.

Studies have shown that postoperative ureteral stricture is potentially linked to thermal damage caused during laser lithotripsy and to the mechanical injury to the ureteral wall by the ureteroscope [24]. A thinner ureteroscope ensures smoother irrigation, which helps reduce the temperature increase caused by high-power laser lithotripsy. The smaller diameter of the 6.3-Fr ureteroscope also provides greater maneuverability, allowing it to pass through narrower ureters and renal calyces, while minimizing direct damage to the ureteral wall. Existing studies have reported that for kidney stones smaller than 2 cm, the efficacy of the 6.3-Fr disposable ureteroscope is superior to that of the 7.5-Fr device [12]. Additionally, the ureteroscope can rotate coaxially by 120°, facilitating access to areas that are difficult to reach with traditional instruments. In the present case, the patient showed a significant reduction in bilateral hydronephrosis on follow-up ultrasound at 1 and 3 months postoperatively, indicating that the ureters were patent and no stricture had occurred, suggesting that the 6.3-Fr ureteroscope has a potential advantage in reducing the risk of postoperative ureteral stricture. The thinner scope also holds significant promise for future applications in pediatric urolithiasis, as the average diameter of the pediatric ureter is approximately 3.8 mm, which poses certain requirements for the instruments [25].

Although the results of this case are encouraging, the 6.3-Fr FURS still has certain limitations. Research indicates that the use of a FVA-UAS during ureteroscopic lithotripsy can effectively improve surgical efficiency and safety. The head of these sheaths passively bends as the ureteroscope bends, allowing it to enter various renal calyces to aspirate stone fragments [26]. We compared the passive bending angles of the 12/14-Fr FVA-UAS when using 6.3-Fr, 7.5-Fr, and 9.0-Fr ureteroscopes, and found that the 6.3-Fr scope resulted in the smallest bending angle, which can increase the difficulty of stone fragment aspiration in the lower pole calyx. For patients with stones primarily located in the lower pole calyx or with narrow and elongated calyces, the stone clearance efficiency of the 6.3-Fr flexible ureteroscope may not show significant improvement, requiring further accumulation of clinical cases for validation. Future studies should further validate its effectiveness in different stone types and complex cases, optimize surgical strategies, and explore more efficient combination therapies.

Conclusions

The 6.3-Fr flexible ureteroscope effectively treated large impacted bilateral ureteral stones in this case, demonstrating the potential advantages of reduced ureteral trauma, a lower risk of postoperative infections, and improved stone-free rates. This technology allows for efficient stone clearance in a single session. However, further large-scale, multicenter studies are needed to confirm these findings and evaluate the broader applicability of this technology in managing complex urolithiasis.