10-Year Experience with Reinforced Ureteral Stents for Malignant Ureteral Obstruction

Malignant upper urinary tract obstruction in cancer patients: A systematic review

Objective

To systematically summarise the current clinical evidence for de novo malignant upper urinary tract obstruction treatment with a focus on standards of reporting, patient outcomes and future research needs.

Methods

This review protocol was published via PROSPERO (CRD42022341588). OVID MEDLINE (R), EMBASE, Cochrane Central Register of Controlled Trials-CENTRAL were searched up to June 2022 in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses. Prospective and retrospective studies were included.

Results

Of 941 articles identified, 82 with 8796 patients were eligible for inclusion.Most studies in the published literature are retrospective and investigate heterogenous malignancies. Percutaneous nephrostomy and ureteric stenting are the most studied interventions. Few studies describe the outcomes from no intervention or investigate patient perspectives. Overall reported median survival after intervention was around 11.7 months. A lack of standardised reporting of outcomes was evident.

Conclusions

Malignant upper urinary tract obstruction is an important clinical condition affecting patients globally. Overall survival after intervention appears poor however the current evidence base has significant limitations due to studies of low methodological quality and the lack of a standardised framework for reporting outcomes.We have provided a pragmatic framework for future studies based on the review to ensure a uniform methodology is utilised moving forward.

It is Possible to Reduce Ureteral Stent Clogging and Stent-Related Symptoms to Soothe the Pain of the Patient: A Case Report

Introduction

Ureteral stent obstruction hinders the management of malignant diseases. Adequate stent insertion through an obstructed ureter does not necessarily guarantee renal decompression and stent-related symptoms adversely affect patient comfort. There are two major problems associated with ureteral stents: obstruction and intolerance to the stents.

Case Presentation

A 45-year-old woman was treated for cervical cancer with metastatic lymph nodes and ureteral obstruction with chemotherapy, radiotherapy, immunotherapy, and bilateral retrograde stenting. After recurrent stent obstruction, stent replacement was attempted more than 18 times over two years. In addition, stent-related symptoms adversely affected patient comfort. The patient was finally fitted with Superglide 8-French reinforced ureteral stents. Their replacement every six months was viewed by the patient as a relief compared to the all too frequent replacement of the previous stents. Moreover, the customized changes in the shape of Superglide stents improved patient comfort.

Discussion

Recent publications tend to indicate that large-lumen ureteral stents are most likely to remain permeable over time. Various modifications of the bladder or endo-ureteral part of double-pigtail stents have been increasingly reported, with the aim of improving their tolerance while maintaining effective drainage.

Conclusion

Adaptation of the internal lumen and shape of stents to the characteristics of the tumor and patient measurements appears to be important for increasing the drainage and tolerance of ureteral stents. The top priority for future ureteral stents suitable for malignant diseases should be to integrate these characteristics based on state-of-the-art data.

Effect of ureteral stent length and implantation position on migration after implantation

BACKGROUND

Ureteral obstruction is a urinary system disease that causes urinary retention, renal injury, renal colic, and infection. Ureteral stents are often used for conservative treatment in clinics, and their migration usually results in ureteral stent failure. The migrations include proximal migration to the kidney side and distal migration to the bladder side, but the biomechanism of stent migration is still unknown.

METHOD

Finite element models of stents with lengths from 6-30 cm were developed. The stents were implanted into the middle of the ureter to analyze the effect of stent length on its migration, and the effect of stent implantation position on 6-cm-long stent migration was also observed. The stents' maximum axial displacement was used to assess the ease of stent migration. A time-varying pressure was applied to the ureter outer wall to simulate peristalsis. The stent and ureter adopted friction contact conditions. The two ends of the ureter were fixed. The radial displacement of the ureter was used to evaluate the effect of the stent on peristalsis.

RESULTS AND DISCUSSION

The maximum migration occurs in the positive direction for a 6-cm-long stent implanted at the proximal ureter (CD and DE), but in the negative direction at the distal ureter (FG and GH). The 6-cm-long stent demonstrated almost no effect on ureteral peristalsis. The 12-cm-long stent diminished the radial displacement of the ureter from 3-5 s. The 18-cm stent diminished the radial displacement of the ureter from 0-8 s, and the radial displacement within 2-6 s was weaker than other time. The 24-cm stent diminished the radial displacement of the ureter from 0-8 s, and the radial displacement within 1-7 s was weaker than other time.

CONCLUSION

The biomechanism of stent migration and ureteral peristalsis weakening after stent implantation was explored. Shorter stents were more likely to migrate. The implantation position had less influence on ureteral peristalsis compared with the stent length, which provided a reference for stent design aimed at reducing stent migration. Stent length was the main factor affecting ureteral peristalsis. This study provides a reference for the study of ureteral peristalsis.

Investigating the encrustation of reinforced ureteral stents by computational flow dynamic simulations

PURPOSE

In cases of extrinsic ureteral obstruction, obstruction due to encrustation is particularly detrimental to functioning of the stent. A thorough understanding of the causes that lead to stent encrustation is essential. Computational fluid dynamic (CFD) simulations may provide a reliable screening platform for investigating the interplay between flow processes and encrustation dynamics in stents.

METHODS

Using a tailor-made program, we attempted to evaluate a number of reinforced ureteral stents by CFD simulations with an obstructed or unobstructed ureter and steady or discontinuous flow patterns to identify critical regions with abrupt changes in shape susceptible to stagnant flow and encrustation.

RESULTS

For the Vortek^® and Urosoft stents, the longitudinal opening of the stents confirmed the presence of critical regions. No critical region was observed for the Superglide stent. CFD simulations showed that cavities formed near the critical regions represented patently stagnant flow and were potentially susceptible to the formation of encrusting deposits. Encrustations were greater in the obstructed design than in the unobstructed design. In the model with a suddenly interrupted laminar flow, the peristaltic motion resulted in new discontinuous encrustation areas scattered throughout the entire external and internal surface of the stent.

CONCLUSION

The analysis of fluid dynamics through the tested stents confirmed that encrustations are possible in regions of stagnant flow and showed that stent models with the smoothest possible surface are preferable. The discontinuous flow model provided results that are closer to the findings observed in the clinic and should be more often integrated into CFD simulations.

Analysis of Ureteral Tumour Stents for Malignant Ureteral Obstruction: Towards Reshaping an Optimal Stent

Introduction

Ureteral obstruction hinders the management of malignant diseases. Adequate stent placement does not necessarily guarantee renal decompression. The stent stiffness may play a major role to maintain patency. We carried out the present study in order to evaluate drainage efficiency by using stents with distinctive degrees of stiffness and to identify the physical factors that could prevent obstruction of the stent in patients with malignant ureteral obstruction (MUO).

Materials and Methods

We performed an analysis of 150 patients with MUO drainage at a single institution from June 2009 to June 2019. A progressive choice of stents was shaped to overcome each failure by focusing on the criterion of increasingly stiff stents.

Results

During the study period, 556 ureteral stent procedures (USP) were analysed separately. The stent failure with obstruction occurred in 23.0% (128/556) of USP at a mean of 4.4±3.6 months and depended on the type of stent. Stent failure occurred in 34.2% (70/205) of Vortek^® stents, in 42.9% (15/35) of Urosoft stents, in 15.4% (39/254) of Superglide or ureteral catheters and in 6.5% (4/62) of tandem stents. No significant differences were found between Vortek^® and Urosoft stents regarding stent failures, but there were significant differences between Superglide or Tandem stents and Vortek^® or Urosoft stents (p<10⁻⁷). The study demonstrated that ureteral stent obstruction significantly decreased with a larger lumen or a stiffer stent (p<10⁻⁷).

Conclusion

In the present study, Superglide and tandem stents were the best stents against stent failure, and the lumen and the stiffness of the stent have been shown to be critical factors in controlling patency. The results suggest that the lumen seems more important than the stiffness, and the stiffness would be the only means of keeping the lumen intact. Future stents for MUO should integrate the importance of the lumen of the stent.

Metal stent for the ureteral stricture after surgery and/or radiation treatment for malignancy

BACKGROUND

To assess the efficacy and safety of self-expanding metal ureteral stent for the stricture following surgery and/or radiation for malignancy.

METHODS

We performed 36 metal ureteral stent insertion procedures (32 patients) between May 2019 and June 2020. The main inclusion criterion was the patients with ureteral stricture due to surgery and/or radiation treatment for malignancy. The diagnosis of stricture was ascertained by history and radiographic imaging. The etiologies underlying the strictures were: surgery and/or radiation therapy for cervical and rectal cancer, surgery for ovarian cancer. The primary outcome was the stent patency rate, and the secondary outcomes were the postoperative complications and glomerular filtration rate (GFR). Stent patency was defined as stent in situ without evident migration, unanticipated stent exchange or recurrent ureteral obstruction. Cost analysis was calculated from stent cost, anesthesia cost and operating room fee.

RESULTS

The pre-metallic stent GFR was 22.53 ± 6.55 mL/min/1.73 m². Eight patients were on double-J stents before insertion of metallic stents. The total annual cost of per patient in our study was $10,600.2 US dollars (range $9394.4-$33,527.4 US dollars). During a median follow-up time of 16 months (range 8-21 months), 27 cases (31 sides, 84%) remained stent patency. Twelve patients died from their primary malignancy carrying a patency stent. Stent migration was observed in 4 patients within 10 months after insertion. Ectopic stents were endoscopically removed and replaced successfully. Three stents were occluded, and no encrustation was seen in our study. Three and four patients had postoperative fever and gross hematuria, respectively. Infection was observed in 2 cases, mandating antibiotics therapy. In addition, postoperative volume of hydronephrosis postoperatively was significantly reduced compared with preoperation (54.18 ± 15.42 vs 23.92 ± 8.3, P = 0.019). However, no statistically significant differences regarding GFR, creatinine levels, blood urea nitrogen and hemoglobin existed between preoperation and last follow-up.

CONCLUSIONS

The current study demonstrated that metal ureteral stent is effective and safe in the treatment of stricture following surgery and/or radiation therapy for malignant cancer. Patients hydronephrosis could be improved by the stent placement.