Simultaneous antegrade–retrograde endoscopic procedures for the placement of thermo-expandable metallic stents in the treatment of ureteral stenosis in kidney transplantation patients: A cohort study

Abstract

Objective

To evaluate the efficacy and safety of simultaneous antegrade–retrograde endoscopic rendezvous procedure for thermo-expandable metallic stent (Memokath 051) placement in treating post-kidney transplantation ureteral stenosis.

Methods

A retrospective single-arm cohort study was conducted in six female patients with distal ureteral strictures after kidney transplantation treated between 2022 and 2024. A dual-endoscope technique was used for stent deployment. Surgical parameters, laboratory indicators, and complications were recorded, with a follow-up period of 1–20 months. Paired t-tests or Wilcoxon tests were applied for statistical analyses.

Results

All stents were successfully placed, with a mean operative time of 173.0 min and mean hospital stay of 8.8 days. Hydronephrosis was significantly relieved in all patients. Postoperative estimated glomerular filtration rate was significantly higher than the preoperative rate (p = 0.04), whereas no significant differences were found between the pre- and postoperative creatinine levels or leukocyte counts. A mild but clinically insignificant hemoglobin drop occurred on postoperative day 1 (p = 0.02). One patient experienced stent migration that was successfully repositioned, and another developed recurrent urinary tract infections that were controlled using antibiotics. All stents remained patent at the final follow-up.

Conclusion

The simultaneous antegrade–retrograde endoscopic approach for Memokath 051 placement appears to be a safe and effective minimally invasive option for post-transplant ureteral stenosis; this finding warrants confirmation in further large-scale multicenter studies.

Keywords

Ureteral stenosis Kidney transplantation Self-expandable metallic stents Endoscope Memokath 051

Introduction

Kidney transplantation is a life-saving treatment that has been used since 1954. Nonetheless, several postoperative complications are associated with kidney transplantation, such as vascular-related conditions, ureteral obstruction, and infectious diseases.¹ Ureteral stenosis is a common urological complication, with an estimated incidence of 3%.² A major cause of ureteral stenosis in kidney transplant recipients is the interruption of ureteral blood flow, causing intimal fibrosis.³ The presence of urological complications is linked to a significant drop in patient survival rates, with ureteral stenosis being the only urological factor associated with reduced kidney graft survival rates.⁴

Herein, we discuss our initial experience with a thermo-expandable metallic ureteral stent in treating ureteral stenosis among six female kidney transplant patients. Further, we describe our surgical technique and technical considerations and provide an initial efficacy and safety assessment. Our research has been published as a preprint.⁵

Methods

The reporting of this small-sample, retrospective, single-arm cohort study conforms to Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines.⁶ The patient was fully informed them that their treatment data may be used in subsequent clinical research and signed a surgical consent form prior to the surgery. The use of this stent has been approved by the Medical Ethics Committee of Beijing Tsinghua Changgung Hospital. We confirmed that all operations were performed in accordance with the relevant guidelines and regulations.

Patients

The study population comprised six female patients who were treated at the department between 2022 and 2024 with a Memokath 051 stent (Pnn Medical A/S; Kvistgaard, Denmark) for ureteral stenosis following kidney transplantation. Consecutive patients were enrolled. The stenotic lesions were located in the distal ureter, including the ureterovesical anastomosis. Table 1 shows the baseline characteristics of the patients. We have deidentified all patient details.

Table 1.

Baseline characteristics of the study population.

N/age/sex	Localization/length(mm)	Stent size(mm)	Cre(μmol/L)	eGFR(mL/min/1.73 m²)	RPW(mm)	Stenosis time since transplantation(months)	Previous treatments	Reason for replacement	Complications
1/33/F	Distal/10	100	115	53.61	20.70	2	DJ stent, nephrostomy, balloon dilation	After the nephrostomy and DJ tubes were removed, hydronephrosis occurred.	Hypertension, UTIs
2/35/F	Distal/10	100	173	32.5	19.10	2	DJ stent, nephrostomy, balloon dilation	Repeated infections after the placement of DJ stents and nephrostomy tubes.	UTIs
3/40/F	Distal/40	150	243	27.60	13.00	4	DJ stent, nephrostomy	The problem of obstruction cannot be resolved.	Hypertension, UTIs, hyperuricemia
4/57/F	Distal/50	150	145	34.47	16.20	2	Nephrostomy	The patient exhibited substandard compliance after the nephrostomy procedure.	Hypertension, UTIs, osteoporosis, GERD
5/61/F	Distal/20	100	259	16.62	14.60	5	DJ stent	At other hospitals, the DJ tube was not successfully inserted.	Hypertension, shingles, UTIs
6/42/F	Distal/50	150	98	61.50	8.00	6	DJ stent	The patient needed long-term need to replace the ureteral stent.	Hypertension, UTIs

eGFR: estimated glomerular filtration rate; Cre: creatinine; Hb: hemoglobin; RPW: renal pelvis width; UTIs: urinary tract infections; GERD: gastroesophageal reflux disease; DJ: double-J; F: female.

Stent placement technique

The stent deployment technique involved a customized surgical strategy based on the clinical status of the patient.

Exploration and guidewire placement

A guidewire was navigated via the pre-existing nephrostomy tract to the renal collecting system. Subsequently, a 14–16Fr percutaneous nephrostomy tract was determined using a fascial dilator. A flexible ureteroscope was placed to investigate and gently remove the original Double-J (DJ) stent. A guidewire was passed through the ureteroscope until it crossed the stenosis and reached the bladder. Subsequently, the guidewire was exteriorized via the urethral orifice using a cystoscope or ureteroscope. A rigid ureteroscope was used for insertion via the urethra where the guidewire encountered difficulty in passing through the stenosis or occlusion anterogradely. The guidewire was then retrogradely advanced through the ureter and bladder anastomosis under dual-scope visualization, passing through the stenotic segment. The guidewire was subsequently grasped anterogradely, ensuring it was exteriorized lateral to the nephrostomy tract.

Dilatation

The ureter was progressively dilated retrogradely using a fascial dilator and flexible ureteroscope sheath up to 14 Fr with the guidewire maintained in a straightened and tensioned position. This procedure was monitored using an anterograde flexible ureteroscope to ensure that the scope sheath completely passed through the stenotic segment. Subsequently, a flexible ureteroscope was used to select an appropriate stent length.

Placement of the stent

A correctly sized Memokath 051 stent assembly, including the metallic stent and delivery sheath, was retrogradely deployed using an anterograde ureteroscope to ensure that the stent’s fluted end traversed the obstructive segment. Alternatively, the assembly was directly inserted anterogradely. Subsequently, the delivery sheath and flexible ureteroscope sheath were retracted, and warmed saline (65°C) was infused concurrently until the stent was fully inflated. Only approximately 2 cm of the stent was positioned inside the bladder, and the excess was cut off using a laser.

Examination

Patency was assessed using anterograde pyelography performed through nephrostomy tubes, with smooth drainage into the bladder showing successful stent deployment.

Nephrostomy tubes were routinely maintained in all patients postoperatively. After a 1-month interval, their removal was determined using anterograde pyelography or ultrasound.

Follow-up and analysis

Patients were discharged if they met the following criteria: (a) postoperative kidneys, ureters, and bladder (KUB) radiography and urography demonstrated secure stent placement and substantial resolution of hydronephrosis and (b) declining trends in infectious markers and creatinine levels on laboratory evaluation compared with preoperative values. All patients required to visit the hospital 1 month after discharge for a follow-up KUB radiography and anterograde urography. If the stent was in place and functioning normally, the nephrostomy tube could be removed. We documented the operative time, hospital stay, pre-and postoperative renal pelvis diameters, pre-and postoperative creatinine levels and eGFRs, preoperative and first postoperative hemoglobin levels, lowest pre-discharge blood leukocyte count, and the incidence of urinary tract infections (UTIs).

Paired t-tests or Wilcoxon tests were performed to assess the efficacy and safety of stent placement. p < 0.05 was considered statistically significant.

Results

All patients were female, were in the age range of 33–61 years, and had undergone nephrostomy or DJ stent placement to relieve obstruction within 4–36 months prior to this hospital admission. Overall, five patients underwent placement of thermo-expandable metallic stents at our center because their existing drainage measures were ineffective; one patient opted for thermo-expandable metallic stents because they were unable to tolerate the frequent replacement of DJ stents.

Stent placement was successful in all patients, with a mean operative time of 173.0 min and average hospital stay of 8.8 days. The mean preoperative renal pelvis width was 15.27 mm. Before discharge, all patients underwent intravenous urography or trans-nephrostomy urography, showing variable improvement in hydronephrosis. The mean preoperative creatinine level was 172.16 μmol/L, whereas that at discharge was 172.67 μmol/L, representing a statistically nonsignificant difference (p = 0.94). We also compared the preoperative and discharge estimated glomerular filtration rates (eGFRs) to find no statistically significant difference between them (p = 0.46). On postoperative day 1, the mean preoperative hemoglobin level was 106.84 g/L, whereas the postoperative level was 101.00 g/L, representing a statistically nonsignificant different (p = 0.02). Regarding infectious indicators, the mean leukocyte count was 6.55 × 10¹²/L preoperatively and reached a postoperative minimum value of 5.79 × 10¹²/L, demonstrating a statistically nonsignificant reduction (p = 0.41). Urine culture results showed that all patients had UTI preoperatively; five of them had asymptomatic bacteriuria, and one experienced abdominal pain; however, no patient had fever. All six patients were administered antibiotics perioperatively, and the urine culture results were reviewed during the postoperative hospital stay. The results were negative in patients with asymptomatic bacteriuria preoperatively, and the bacterial loads in the urine of patients with symptoms (Enterococcus faecium) were reduced. All stents remained properly positioned throughout this duration except in one patient for whom surgical intervention was required due to stent migration. All patients visited the hospital 1 month postoperatively for follow-up antegrade urography and KUB radiography; the results showed that the thermo-expandable metallic stents were well positioned and the contrast medium was draining freely. Consequently, we removed the nephrostomy tubes for all patients. The follow-up period ranged from 1 to 20 months, with a mean duration of 10.3 months. The mean creatinine level at the final follow-up was 149.00 μmol/L, which was lower than the preoperative mean level; however, this reduction was not statistically significant (p = 0.13). Figure 1 shows the perioperative and follow-up creatinine levels. However, the eGFR reviewed at the final follow-up was significantly higher than the preoperative value (p = 0.04).

Figure 1.

Changes in creatinine levels (μmol/L) before and after stent placement.

Discussion

The decision to undertake open or minimally invasive surgery is a debated issue among surgeons because different surgical interventions yield varying prognoses. In the case of distal ureteral stenosis, open surgery has demonstrated higher success rates than minimally invasive methods, both in initial and secondary therapies.

Ureteral reimplantation is a common open treatment with a remarkable success rate of up to 82.4%.⁷ However, open surgery is commonly associated with increased bleeding, prolonged hospital stays, and longer recovery periods. Minimally invasive techniques typically encompass nephrostomy, balloon dilatation, stent placement, and endo-ureterotomy of the stenotic segment. Nevertheless, the recurrence rates following these procedures are high, with patients exhibiting significantly lower graft survival rates than recipients without ureteral stenosis.⁴ Regardless of the minimally invasive surgical procedure used, postoperative placement of a ureteral stent is routine practice because it can effectively prevent obstruction, colic, and renal failure due to postoperative ureteral edema or passage of debris, including stones and blood clots and reduce the need for reoperation due to urological complications.⁸ However, ordinary DJ stents remain prone to clinically significant complications, including encrustation, migration, infection, pain, medical injury, and even increased graft damage.^9,10

In response to these complexities, novel metal stents have been developed. Herein, we present an initial summary on metallic stents that have been used over the past decade for ureteral stenosis after kidney transplantation (Table 2).^11–15 A helically structured thermo-expandable nickel–titanium metallic stent, the Memokath 051 stent, has been used in patients with ureteral stenosis after kidney transplantation. This stent has been endorsed by the National Institute for Health and Care Excellence for benign and malignant ureteral strictures because of its complete removability, low pain rate, capacity to prevent endothelial ingrowth, corrosion resistance, and magnetic resonance imaging compatibility.¹⁶ Additionally, this metallic stent has demonstrated good long-term efficacy, with arguably a maximum follow-up duration of 114 months.¹⁷ Herein, we provide relevant literature citations demonstrating the outcomes of this stent (Table 3);^18–21 however, recent research remains limited.

Table 2.

Characteristics of metal stents used over the past decade.

Study	Patients	Type of stent	Follow-up duration (months)	Characteristics
Xu et al.¹¹	7	AnDaXing	13–86	Technical success rate (100%), lower urinary-tract symptoms (6/7), ipsilateral flank pain (4/7), urothelial hyperplasia-induced obstruction (1/7)
Sedigh et al.¹²	1	UVENTA	12	No complications, stable renal function, and no signs of recurrence after removal
Salamanca-Bustos et al.¹³	5	UVENTA	4–38	Technical success rate (100%), renal graft loss (1/5), UTI (1/5), hydronephrosis correction rate (100%)
Zhong et al.¹⁴	8	Allium	5–17	Success rate (86%), release of obstruction (100%), stent migration (2/8)
Cao et al.¹⁵	8	Urexel	2–27	Hematuria (2/8), pain (3/8), stent migration (2/8), urothelial hyperplasia (2/8), recurrence (2/8)

UTI: urinary tract infection.

Table 3.

Characteristics of Memokath 051 used to treat transplant ureteral stenosis.

Study	Patients	Follow-up duration (months)	Characteristics
Boyvat et al.¹⁸	4	18–21	Technically success rate (100%), stent migration (1/4), UTI (1/4)
Bach et al.¹⁹	1	27	Successfully replaced a previously placed metal self-expanding mesh stent without the previous problems of encrustation and endothelial ingrowth.
Bach et al.²⁰	8	55 (mean)	Long-term success rate (87%), stent migration (1/8), spontaneous resolution of the stricture (3/8)
Treacy et al.²¹	1	36	One week postoperatively, there was a considerable reduction in the serum creatinine level and complete restriction of the pelvic dilation, with no complications during follow-up.

UTI: urinary tract infection.

Regarding the efficacy of our procedure, in all patients, hydronephrosis was significantly alleviated at hospital discharge, promptly relieving pressure on the kidneys. However, no significant change was observed between the pre- and postoperative creatinine levels. This may be attributed to the relatively short follow-up period, which did not allow significant recovery of renal function. Miernik et al. used the Memokath 051 stent to treat ureteral anastomotic stenosis in six patients and observed no statistically significant difference in their renal function before and 3 months after surgery.²² Nonetheless, this stent is shown to effectively mitigate the deterioration of renal function among patients. Johnson has also demonstrated that the longer the duration of obstruction, the more difficult the recovery of renal function.²³ A review of their data revealed that in all patients, hydronephrosis was present at least 4–36 months before admission. Therefore, although the obstruction was released, recovery of the long-term damage to renal function was difficult during the follow-up period. However, a statistically significant difference in the eGFR was observed between the preoperative and final follow-up assessments, suggesting that the placement of this stent restored the patients’ renal function to a certain extent. The lack of statistically significant reduction in their creatinine levels may be attributed to insufficient statistical power due to the small sample size. This study did not include cystatin C or other more sensitive markers of renal function as core assessment endpoints; this constitutes a significant limitation of the study, which we intend to address in future research. Studies have indicated that the rate of cystatin C production is relatively constant and is not significantly influenced by muscle mass, sex, ethnicity, or diet.^24,25 Therefore, it provides a more reliable estimate of renal function than creatinine levels in patients with reduced muscle mass (such as older adults and those suffering from malnutrition) or abnormal muscle mass (such as amputees and obese individuals).²⁶

In relation to the safety assessment, a statistically significant difference was observed between the pre- and postoperative hemoglobin levels. However, this decrease was not considered to be clinically significant because the reduction was minimal. Furthermore, no significant amount of visible bleeding was observed during the procedure, which suggested that the drop in hemoglobin level was not related to the procedure. It is hypothesized that the decrease was related to the patients’ chronic infectious state during hospitalization. Previous studies have suggested that inflammatory anemia, also known as chronic disease anemia, is the most common type of anemia among hospitalized and chronically ill patients. The mechanism of its occurrence is believed to be related to systemic immune activation that can lead to impaired iron transport, impaired iron- and liver-dependent erythropoiesis, and a shortened erythrocyte lifespan in the inflammatory milieu.²⁷ This decrease may also be related to the perioperative rehydration, resulting in hemodilution. All six patients had UTIs after admission; however, five of them experienced remission of UTIs after the procedure. We believe that the perioperative use of antibiotics and effectiveness of the stent in relieving urinary tract obstruction were instrumental in curing the UTIs. In one patient, recurrent Enterobacter cloacae was identified on urine culture 1 month postoperatively, and Enterobacter faecalis appeared was identified on urine culture 3 months postoperatively. Considering that this patient also had recurrent UTIs before the metal stent was placed, these findings suggests that the cause of the recurrent UTIs was not this stent. In addition, computed tomography demonstrated that the patient did not have hydronephrosis, indicating that the stent was still functioning. Therefore, we did not remove the metal stent, but continued to administer anti-infection treatment. We considered it plausible that the UTIs resulted from the triple immunosuppressive therapy and long-term bacterial colonization. Conversely, the stent still alleviated hydronephrosis, which we believed helped in treating the infection. It is worth noting that UTIs, especially recurrent UTIs, are an important risk factor for allograft loss. Therefore, in infected patients, it is crucial to identify the source of infection and control it.²⁸ Following a prolonged course of anti-infective treatment, the patient exhibited no infection-related clinical symptoms at the final follow-up. Urine culture continued to demonstrate low-level colonization of Enterococcus faecalis; however, no acute exacerbations occurred, and renal function remained stable. Taken together, although metal stents theoretically pose a risk of becoming a source of infection, in clinical decision-making, the relief of ureteral obstruction and protection of graft function are consistently prioritized. Stent removal is only considered when infection is uncontrollable and threatens graft safety.

Another patient experienced distal migration of the stent on postoperative day 2 (Figure 2(a)). Trans-nephrostomy urography revealed significant contrast accumulation in the renal pelvis and proximal portion of the stent (Figure 2(b)). Additionally, this patient exhibited a significant peak in creatinine levels during the postoperative review. Based on an extensive literature review, the incidence rate of stent migration ranges from 7.7% to 46.2%, making it the most common complication linked to this particular procedure.²⁹ Potential explanations for such migration include inaccurate estimation of stenosis length and inadequate anchoring due to ureteral overdistension.³⁰ A “double insurance” approach was used to accurately estimate the length of the stenosis. The preoperative visualization of the stenosis location and length was achieved using urography, whereas a flexible ureteroscope was utilized intraoperatively. This technique is more accurate than the conventional technique, which involved retrograde and/or anterograde urography and marking the extent of stenosis with a metal probe on the lateral aspect of the anterior abdominal wall.³¹ Balloon dilators should be avoided to prevent overdistension.³² Thus, we exclusively used either a fascial dilator or flexible ureteral sheath during placement. In this patient, we positioned the stent at the renal pelvis and ureteral junction for improved drainage due to the tortuous nature of the ureter. Nonetheless, most of the stents resided in the normal section since the stenotic segment was only approximately 1 cm distal to the ureter. Stent migration toward the distal direction occurred due to ureter dilation caused by hydronephrosis and peristalsis. Therefore, stents that significantly exceed the length of strictures should be avoided. Contrast accumulation may not be caused solely by migration but could also result from potential blood clots or tissue obstruction within the stent. Surgery was immediately performed for stent repositioning. First, the bladder was accessed via a retrograde ureteroscope, and the metal stent was curled up inside the bladder. A laser was used to excise approximately 5 cm of the distal end before placing a guidewire and a thinner DJ inside the metal stent to dredge it and intraoperatively observe drainage of the clot. Intraoperative drainage successfully resolved the blood clot, preventing further stent migration during postoperative imaging and subsequent follow-up (Figure 2(c)). Subsequently, preventive measures were implemented by reintroducing a transplant kidney-specific DJ stent inside the metal stent for patients with substantial intraoperative bleeding or unsatisfactory intraoperative urography results (Figure 3). This approach was adopted in another patient, wherein successful removal of the DJ stent occurred 1 month postoperatively without any discomfort or lumen blockage. A review in the field of gastrointestinal endoscopy has suggested that for the drainage of accumulated pancreatic fluid, the strategy of placing a double-pigtail plastic stent coaxially within a lumen-apposing metal stent helps reduce the risk of stent occlusion and infection; the principle behind our management strategy may be similar.³³ However, our strategy should be employed as a selective preventive measure, reserved solely for high-risk patients with significant intraoperative bleeding or complex anatomical structures that may lead to poor drainage, rather than as a routine procedure for all patients. This is because long-term placement of ureteral stents can lead to infection, encrustation, stent migration and the resulting secondary injuries.^34,35

Figure 2.

(a) The stent migrated distally, and the caudal end is coiled in the bladder. (b) Contrast agent accumulates in the renal pelvis and proximal part of the stent. (c) KUB after the stent has been adjusted for position and length. KUB: kidneys, ureters, and bladder.

Figure 3.

A special DJ stent for transplanted kidneys is placed inside the metallic stent. DJ: double-J.

Regarding the surgical approach, we used simultaneous access to the urinary tract via both anterograde and retrograde approaches, also known as the rendezvous procedure. A combined ureteroscope and cystoscope were used to explore the stenotic segment and place a guidewire. A stent was placed under full endoscopic surveillance. However, unlike the procedure described by Mazzon et al.,³⁶ our procedure did not require a radiologist to perform an anterograde pyelogram to visualize the ureteral injury or stenosis intraoperatively. However, we concur with the essential steps of renal surgery. The guidewire was inserted via the stenotic segment of the ureter under dual-scope vision, ensuring complete traversal from the nephrostomy end to the urethral orifice, thereby establishing a comprehensive “pathway” (Figure 4). The placement of the ureteral stent is performed under direct visualization, ensuring accurate execution of the procedure. Due to the tortuous ureter of the transplanted kidney, the process of placing guidewires and stents can easily damage the ureteral mucosa. This method, which allows direct visualization of the surgical procedure, can precisely prevent such damage. Furthermore, if intraoperative findings, including ureteral stones, which necessitate intervention are observed, they can be effectively managed under direct endoscopic visualization.

Figure 4.

Guidewire passage through the entire urinary tract.

Although this technique offers a minimally invasive treatment option for post-kidney transplant ureteral strictures, it still has certain key limitations. The procedure requires the surgeon to be proficient in both nephrostomy techniques and manipulation of ureteroscopes or cystoscopes; as such, it is difficult for practitioners in primary care hospitals or those with limited endoscopic experience to replicate quickly, and there is a clear learning curve. Furthermore, all the cases included in this study had short-segment strictures of the distal ureter (uretero-vesical anastomosis) following kidney transplantation, with the longest stricture segment measuring 50 mm; this procedure is best suited to such lesions. However, the efficacy of this technique in cases involving long-segment ureteral strictures, multiple strictures, proximal strictures at the ureteropelvic junction, and complete ureteral obstruction remains unknown. In fact, it may not even be feasible to perform the procedure in such cases. Furthermore, the imported stents and instruments used in this procedure are significantly more expensive than standard DJ stents, and their use would impose a heavy financial burden on patients, severely limiting the clinical utilization of this procedure in primary care hospitals and economically underdeveloped regions.

Conclusion

To the best of our knowledge, this is the first study to report the use of thermo-expandable metallic stents in patients with kidney transplantation and ureteral strictures, utilizing a dual-endoscope technique. As our study included only six patients, with a maximum follow-up period of 20 months, it cannot definitively establish the safe and effectiveness of this technique. However, our study represents an exploratory attempt that holds potential for providing a novel treatment option for patients with post-kidney transplantation ureteral strictures. We intend to conduct prospective, multicenter, large-scale studies with long-term follow-up to demonstrate the benefits and limitations of our technique.

Footnotes

Acknowledgments

We would like to acknowledge Ms. Su and Mr. Shouyu Miao for their supporting work in this study.

Author contributions

Xuming Zhang: conceptualization (equal contribution), writing-original draft (lead), formal analysis, and data curation. Chaoyue Ji: writing-review. Weiguo Hu: conceptualization and supervision.

Data availability statement

All data supporting this study are included in this manuscript and its supplementary materials.

Declaration of conflicting interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ethics statement

This study was approved by the Beijing Tsinghua Changgung Hospital Ethics Committee in accordance with the relevant laws and policies, including the National Health Commission’s “Measures the Ethical Review of Biomedical Research Involving Human Subjects (2023),” the State Drug Administration/National Health Commission’s “Quality Control Standards for Clinical Trials (2020)” and Quality Control Standards for Medical Device Clinical Trials (2022),” the Declaration of Helsinki (2013), and the Council for International Organizations of Medical Sciences (CIOMS) “International Ethical Guidelines for Health-related Research Involving Humans.” All patients signed an informed consent form prior to surgery.

Funding

No funding was received for conducting this research.

ORCID iD

Weiguo Hu

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