A Self-Expanding Thermolabile Nitinol Stent as a Minimally Invasive Treatment Alternative for Ureteral Strictures in Renal Transplant Patients

Early encrustation of a ureteric metallic stent managed by robotic assisted extraction and pyeloplasty

Ureteral obstruction is a commonly encountered condition during daily practice. The mainstay of treatment for ureteral obstruction is drainage and relief of the obstruction, regardless of the etiology. Drainage using the traditional ureteral Double J stent has been recently challenged with new ureteric stent that proposed to have better durability and patient quality of life, particularly in cases that require prolonged insertion. One of these options are the ureteric metallic stents, such as Memokath, although uncommon, encrustation of Memkath can occur, leading to early removal. Here we present a case of 28-year-old gentleman with recurrent right pelviureteric junction obstruction, who had undergone pyeloplasty in childhood, The patient was hesitant to undergo redo pyeloplasty and opted for balloon dilatation with Memokath insertion. however early encrustation occurred leading to worsening of the condition and pain, and he was subsequently managed with robotic assisted laparoscopic Memokath extraction and dismembered pyeloplasty.

A new technique for the treatment of ureteric stricture after kidney transplantation

OBJECTIVE

To evaluate the safety and effectiveness of endoscopic treatments with Allium® metal ureteric stent (AMUS) for ureteric strictures after kidney transplantation (KT).

PATIENTS AND METHODS

In a prospective manner, we gathered clinical data from 68 patients who underwent endoscopic treatments with AMUS for ureteric strictures after KT between January 2019 and March 2022. The definition of surgical success was the unobstructed drainage of the AMUS, or in cases where there was AMUS migration, occlusion or encrustation and subsequently removed, there is no worsening of renal hydronephrosis in the patient during the follow-up period.

RESULTS

Based on the specific circumstances of the ureteric strictures, three distinct types of surgery were selected for treatment. The overall success rate of endoscopic treatments for ureteric strictures following KT was 90% (61/68) during a follow-up period of 1 year. Surgical complications included haematuria (18%), pain (10%), urinary tract infections (7.4%), and lower urinary tract symptoms (7.4%). The incidences of stent migration, occlusion, and encrustation were 10%, 2.9%, and 1.5%, respectively. Postoperatively, significant improvements were observed in various parameters. At 1 month after surgery, there was a notable decrease in blood creatinine levels (105.5 vs 90.4 mol/L), urea nitrogen levels (6.6 vs 5.4 mmol/L), and hydronephrosis volume (64.4 vs 43.9 mL). Additionally, the serum estimated glomerular filtration rate increased from 49.5 to 64.4 mL/min/1.73 m2. The follow-up results of patients at 1 year after surgery were similar to those observed at 1 month after surgery.

CONCLUSIONS

Systemic endoscopic treatments with AMUS were found to be safe and effective for ureteric strictures after KT with short-term follow-ups. This technique offers a novel option for the treatment of post-KT strictures.

Metal ureteral stents for ureteral stricture: 2 years of experience with 246 cases

BACKGROUND

Metal ureteral stents (MUS) has gained popularity as an endoscopic treatment alternative for the management of ureteral strictures. The aim of this study was to evaluate the safety, efficacy, and tolerability of MUS for treating ureteral strictures and to identify any factors that could influence the success of this intervention.

METHODS

This study is a prospective analysis of the efficacy and safety of MUS for treating ureteral strictures in a single-center setting. The study enrolled 246 patients who had been diagnosed with ureteral strictures and had undergone MUS placement between January 2019 and July 2021. The patients were followed-up for a duration of 2 years.

RESULTS

The overall success rate of MUS placement was 71.7%. Furthermore, the success rate of ureteral strictures after kidney transplantation (78.2%) was significantly higher than common ureteral strictures (73.0%) or recurrent ureteral strictures (67.6%). Additionally, postsurgery, there was a considerable reduction in hydronephrosis volume (68.9±96.1 vs. 32.1±48.8 cm 3 ), blood creatinine level (103.7±49.8 vs. 94.4±47.5 mol/l) and urea nitrogen level (6.7±7.2 vs. 5.1±2.4 mmol/l). The study also reported that the rate of adverse events associated with MUS was relatively low, included hematuria (7.9%), pain (6.8%), urinary tract infection (6.4%), and lower urinary tract symptoms (5.3%).

CONCLUSIONS

MUS appear to be a safe and effective treatment option for ureteral strictures, with a high success rate and low complication rate. These results have important implications for the management of ureteral strictures and can help guide clinical decision-making in the selection of treatment options.

Modern surgical strategies in the management of complex ureteral strictures

PURPOSE OF REVIEW

The purpose of this article is to outline the various therapeutic options of ureteral strictures.

RECENT FINDINGS

Ureteral strictures with consecutive hydronephrosis can be due to endourological and surgical procedures, inflammatory processes, radiation therapy as well as spontaneous passage of ureteral calculi. When planning surgical correction, stricture length, anatomical location as well as patients' characteristics like age, comorbidities and previous treatment in the peritoneal cavity, retroperitoneum or pelvis should be taken into consideration. Treatment options include not only surgical reconstruction techniques like simple stricture excision, end-to-end anastomosis, ureterolysis with omental wrapping, ureteroneoimplantation, renal autotransplantation and ureter-ileum replacement, but also minimally invasive procedures such as self-expandable thermostents and pyelovesical bypass prosthesis.

SUMMARY

Various therapeutic options can be offered in the treatment of ureteral strictures, potentially leading to long-term success rate of more than 90% and a rate of significant complications < 5%.

Minimal-invasive management of urological complications after kidney transplantation

Kidney transplantation represents the gold standard treatment option for patients with end-stage renal disease. Improvements in surgical technique and pharmacologic treatment have continuously prolonged allograft survival in recent years. However, urological complications are frequently observed, leading to both postoperative morbidity and putative deterioration of allograft function. While open redo surgery in these patients is often accompanied by elevated surgical risk, endoscopic management of urological complications is an alternative, minimal-invasive option. In the present article, we reviewed the literature on relevant urological postoperative complications after kidney transplantation and describe preventive approaches during the pre-transplantation assessment and their management using minimal-invasive approaches.

Temporary Covered Metallic Ureteral Stent Placement for Ureteral Strictures following Kidney Transplantation: Experience in 8 Patients

This brief report presents 8 patients with silicone-covered metallic stent placement for ureteral strictures refractory to double-J stent placement, following kidney transplantation. Stent removal was successfully performed in 7 patients via antegrade (n = 4) or retrograde (n = 3) access 6 weeks to 6 months after stenting for elective removal (6-month interval, n = 3), urothelial hyperplasia (n = 2), or stent migration (n = 2), and their mean primary ureteral patency after stent removal was 15.4 months (range, 2-27 months). Hematuria (n = 2) and pain (n = 3) occurred, but resolved within 1 week. One stent was removed during reconstructive surgery. During follow-up of mean 22.6 months after stent removal, ureteral strictures recurred in 2 patients.

Minimally invasive management of ureteral strictures: a 5-year retrospective study

Introduction

Ureteric strictures are well-documented complications related to surgery or radiation therapy. Minimally invasive treatment using endoscopic dilatation or laser incision is the standard practice. There are no existing guidelines on which techniques to use in the treatment of different stricture types and a paucity of data regarding long-term results.

Purpose

Our study aimed to retrospectively assess the long-term efficacy of minimally invasive treatment in benign and malignant ureteric strictures.

Materials and methods

Over a 5-year period, 2007–2012, we analyzed the data of 59 consecutive patients undergoing minimally invasive treatment for symptomatic ureteric strictures. We excluded 16 patients from final analysis due to failed access or loss to follow-up. All patients but one were treated with antegrade, retrograde balloon or catheter dilatations. Successful outcome was defined as an asymptomatic, completely catheter free patient, with stable renal function.

Results

43 patients were eligible for retrospective final analysis. The largest proportion of strictures occurred following surgery combined with radiotherapy 8/43 (19%). Preoperative decompression was required in 30/43 (70%). We identified 32/43 (75%) balloon dilatations, 10/43 (23%) catheter dilatations and 1/43 (2%) laser incision. Overall success rate was 31/43 (72%). All 6 recurrences occurred within 36 months, 4 within the first 12 months. 3/6 patients were successfully re-dilated.

Conclusion

Minimally invasive treatment is a worthwhile alternative in strictures due to previous radiation and/or surgical treatment of malignancies. Most recurrences occurred within the first year. However, late recurrences arise; therefore, patients should be subject to long-term follow-up. Moreover, re-dilatation may be required.

Self-Expandable Covered Metallic Stent (UVENTA) to Treat a Ureteral Stricture After Renal Transplant: A Case Report

We present the use of a self-expandable covered metallic stent (UVENTA; TaeWoong Medical, Gyeonggi-do, South Korea) to treat a ureteral stricture after kidney transplant. In this report, we describe the procedure and short-term outcomes of a patient with a recurrent distal stricture who did not respond to percutaneous balloon dilation. We decided to place this temporary stent as an alternative to complex surgery. The aim of the procedure was to get a chronic dilation of the stricture up to 7 mm to stabilize the fibrotic tissue. The procedure was easily and quickly performed by an antegrade and retrograde combined approach. The postoperative course was uneventful. The stent was left in situ for 7 months. No complications were noted, and the renal function remained stable. The stent was easily removed, and 5 months later there were no signs of recurrence. The UVENTA device was shown to be an easy, safe, and effective minimally invasive treatment for ureteral stricture in renal transplant. Proper permanence time and long-term results need to be explored.

The Memokath-051 Stent for the Treatment of Ureteric Obstruction: A NICE Medical Technology Guidance

Memokath-051 is a thermo-expandable, nickel-titanium alloy spiral stent used to treat ureteric obstruction resulting from malignant or benign strictures. The National Institute for Health and Care Excellence (NICE) selected Memokath-051 for evaluation. The company, PNN Medical, claimed Memokath-051 has clinical superiority and cost savings compared with double-J stents. It identified five studies reporting clinical evidence on Memokath-051 and constructed a de novo cost model comparing Memokath-051 to double-J stents. Results indicated that Memokath-051 generated cost savings of £4156 per patient over 2.5 years. The External Assessment Centre (EAC) critiqued the company's submission and completed substantial additional work. Sixteen studies were identified assessing Memokath-051 and all listed comparators in the scope (double-J stents, reconstructive surgery and metallic and alloy stents) except nephrostomy. Similar success rates were reported for Memokath-051 compared with double-J and Resonance stents and worse outcomes compared with other options with evidence available. The EAC updated the company's cost model structure and modified several inputs. The EAC's model estimated that Memokath-051 generated savings of at least £1619 per patient over 5 years compared with double-J stents, was cost neutral compared with other metallic stents and was cost saving compared with surgery up to month 55. Overall, Memokath-051 is likely to be cost saving in patients not indicated for reconstructive surgery and those expected to require a ureteral stent for at least 30 months. The Medical Technologies Advisory Committee (MTAC) reviewed the evidence and supported the case for adoption, issuing partially supportive recommendations published after public consultation as Medical Technologies Guidance 35.

Initial Experience in the Use of Novel Auto-expandable Metal Ureteral Stent in the Treatment of Ureter Stenosis in Kidney Transplanted Patients

INTRODUCTION

Ureter stenosis in renal transplantation patients is a relatively frequent complication that negatively conditions graft evolution. The use of ureteral stents is a valid treatment alternative to the use of double-J catheters in patients for whom surgery is not contemplated or after surgical recurrence. We present our initial experience with five patients treated using this technique.

MATERIALS AND METHODS

We describe a total of five patients with ureteral stenosis after renal transplantation who were treated using ureteral stent model UVENTA (Taewoong Medical, Seoul, Korea) in our center. The median follow-up was 18 months (range, 4 to 38 months). We describe the clinical history of patients and previous treatments on ureteral stenosis. The technical procedure of placement is described. The clinical course is analyzed by measurement of renal function and imaging tests, as well as post-stent complications. Survival of the renal graft is evaluated.

RESULTS

The procedure could be completed in all patients without complications. The technique was effective in all patients, with correction of creatinine value and hydronephrosis during the renal ultrasound test. One patient suffered a urinary tract infection episode associated with the use of the ureteral stent. One patient suffered the loss of the renal graft secondary to the development of cryoglobulins. One hundred percent of the ureteral stents are functioning as of the writing of this article.

CONCLUSIONS

In renal transplantation patients with ureter stenosis, metallic stents are a useful technique with low morbidity and associated complications.

A Comparison of Two Configurations for a Dual-Resonance Cymbal Transducer

The ability to design tuned ultrasonic devices that can be operated in the same mode at two different frequencies has the potential to benefit a range of applications, such as surgical cutting procedures where the penetration through soft then hard tissues could be enhanced by switching the operating frequency. The cymbal transducer has recently been adapted to form a prototype ultrasonic surgical cutting device that operates at a single frequency. In this paper, two different methods of configuring a dual-resonance cymbal transducer are detailed. The first approach relies on transducer fabrication using different metals for the two endcaps, thereby forming a dual-resonance transducer. The second employs transducer endcaps composed from a shape memory alloy, superelastic Nitinol. The resonance frequency of the Nitinol transducer depends on the phase microstructure of the material, switchable through the temperature or stress dependence of the Nitinol endcaps. The vibration response of each transducer is measured through electrical impedance measurements and laser Doppler vibrometry, and finite-element analysis is used to show the sensitivity of transducer modal response to the fabrication processes. Through this paper, two viable dual-resonance cymbal transducers are designed and characterized and compared to illustrate the advantages and disadvantages of the two different approaches.

The thermoexpandable nitinol stent: a long-term alternative in patients without nephropathy or malignancy

OBJECTIVE

The aim of this study was to investigate the long-term outcome of a thermoexpandable nickel-titanium nitinol ureteral stent (Memokath 051™) and to identify individual risk factors for failure.

MATERIALS AND METHODS

This retrospective single-centre study included 125 patients who underwent implantation of the self-expandable Memokath 051 stent. Complications, indwelling time and reason for explantation were recorded. Analyses were stratified by gender, age, body mass index, American Society of Anesthesiologists score, estimated glomerular filtration rate (eGFR), side, localization and cause of the stricture.

RESULTS

In total, 91 out of 125 patients (73%) were available for analysis. Median indwelling time was 355 days (range 7-2125 days). Most stents were removed because of dislocation (42%) or occlusion (40%). Stent removal was rarely performed because of infection (3%). Patients with sufficient renal function (eGFR ≥60 ml/min/1.73 m²) showed increased indwelling times compared with those with nephropathy (386 vs 317 days; p < 0.01). Patients with active malignant disease showed reduced patency time compared with strictures of benign origin (455 vs 190 days; p < 0.01).

CONCLUSIONS

This thermoexpandable nitinol stent offers safe mid-term treatment of ureteric strictures, especially in patients without active malignancy and with good renal function.

Use of Self-Expanding Metallic Ureteral Stents in the Secondary Treatment of Ureteral Stenosis Following Kidney Transplantation

INTRODUCTION

To evaluate the safety and efficacy of self-expanding metal stents in the treatment of ureteral stenosis following kidney transplantation.

MATERIALS AND METHODS

Seven patients who developed benign stenosis after kidney transplantation were treated by a self-expanding metallic stent implantation from June 2007 to March 2014. All patients had undergone at least one open surgical procedure and one endourologic procedure for treatment of the stenosis. The extent of stenosis varied from 1.2 to 3.7 cm. Ultrasonography, urography, diuretic renography, and urine culture were performed every 3 months after stent insertion. Ureteroscopic examination was performed when needed.

RESULTS

Stent placement was technically effective in all cases. The mean operative time was 37 minutes (range, 26-59 minutes). Lower urinary-tract symptoms and the ipsilateral flank pain were common early-stage complications and were greatly relieved after an average of 3 months. The mean follow-up duration was 38 months (range, 13-86 months), and no stent migration or fragmentation was observed. Urothelial hyperplasia occurred in only one patient and was effectively managed with a Double-J stent. Five patients had normal stable renal function; the remaining two had impaired renal function, including one patient with a preoperative renal failure who required dialysis at the end of the follow-up period (36 months).

CONCLUSIONS

As an alternative to open surgery, implantation of a self-expanding metal stent is a safe and effective treatment for ureteral stenosis in patients who have undergone kidney transplantation.

Ureteral strictures revisited…trying to see the light at the end of the tunnel: a comprehensive review

A ureteral stricture is a rather rare urological event defined as a narrowing of the ureter causing a functional obstruction and renal failure, if left untreated. The aim of this review article is to summarize and discuss current knowledge on the incidence, pathogenesis, management, and follow up of proximal, mid, and distal ureteral strictures.