ACE2 and angiotensin 1-7 are increased in a human model of cardiovascular hyporeactivity: pathophysiological implications

Evaluation of Renal Function and Stent Durability Following Resonance Stent Placement for Benign Disease

Introduction: The metal-based Resonance stent (RS) has traditionally been placed in patients with malignant ureteral obstruction; as such, the long-term utility of RS among patients with benign ureteral obstruction (BUO) remains underinvestigated. Methods: We retrospectively reviewed our database for patients with BUO who underwent RS placement between 2010 and 2020. The impact of chronic RS placement on renal function was evaluated by estimated serum creatinine-based glomerular filtration rate (eGFR), furosemide renal scan, and CT-based renal parenchymal volume measurement. The number of and reason for RS stent exchanges during the follow-up period, incidence of encrustation, and the average indwell time were recorded. A cost analysis of placing the RS vs a polymeric stent was performed. Results: Among 43 RS patients with BUO, at a mean follow-up of 26 months, there was no change in eGFR (p = 0.99), parenchymal volume (p = 0.44), or split renal function of the stent-bearing side on renal scan (p = 0.48). The mean RS indwell time was 9.7 months. Eleven patients (26%) underwent premature stent replacement (6 cases) or removal (5 cases). Stents in 9 patients (32%) were encrusted, of which 4 (44%) required laser lithotripsy. Overall, 25 patients (58%) and 12 patients (28%) had a mean stent indwell time of ≥6 months and ≥12 months, respectively. Placing an RS resulted in a 52%, 37%, and 5.6% cost reduction compared with a regular polymeric stent placement, where it was exchanged every 6, 4, or 3 months, respectively. Conclusions: RS deployment in the patient with a BUO results in cost-effective maintenance of renal function and of renal parenchymal volume at a mean follow-up of 2 years; however, only 28% of patients fulfilled the 1-year criterion for RS indwell time.

Evaluation of Galdakao-modified Valdivia position in endoscopic management of malignant ureteric obstruction

Background

Malignant ureteric obstruction (MUO) due to pelvic malignancies is challenging for endourological management and carries high failure rates for retrograde cystoscopic ureteric stenting.

Methods

We adopted Galdakao-modified Valdivia (GMV) position in the management of MUO in an operating room equipped with a C-arm fluoroscopy unit and an ultrasound device. We prospectively studied the added value of this approach in 50 cases who failed retrograde ureteric stenting.

Results

Thirty-seven (74%) cases were done under a high level of spinal anesthesia. Mean operative time was 62 min. Antegrade ureteric stenting succeeded in 45/50 (90%) patients who failed retrograde ureteric stenting. GMV position facilitated simultaneous retrograde and antegrade management of MUO. Eight patients (16%) underwent auxiliary cystoscopic procedures to reduce the mass over the ureteric orifice (UO) guided by antegrade methylene blue or over a probing antegrade guidewire. Nephrostomy tube was inserted in the same setting in 16/50 (32%) cases. Antegrade flow of contrast to the bladder (P < 0.001) and ureteric kinks rather than tight stenosis or infiltration of UO (P = 0.014) were significantly associated with the success of antegrade ureteric stenting. No major complications were encountered.

Conclusion

GMV position is an ideal choice for management of MUO as it allows simultaneous access to the lower and the upper urinary systems to accomplish ureteric stenting either in a retrograde or an antegrade fashion as well as the ability to insert a nephrostomy tube in the same setting, thus shortening the inpatient care and this should be the standard of care in cases with MUO.

Self-expanding metal ureteral stent for ureteral stricture: Experience of a large-scale prospective study from a high-volume center - Cross-sectional study

BACKGROUND

The management of ureteral stricture is still a challenge for urologists. The aim of this prospective study was to assess the safety and effectiveness of self-expanding metal ureteral stents (URS) in ureteral strictures.

METHODS

We performed URS placement procedures for ureteral stricture from Jan 2019 to July 2020, and prospectively collect various data before and after the operation. A paired T test was used to compare continuous variables before and after surgery, binary logistic regression analysis was used to identify the independent risk predictors of surgical failure.

RESULTS

A total of 147 patients with 157 renal units received successful placement of URS. The mean operative time was 70.0 min. After a median follow-up time of 15 months, 73.2% (115/157) of stents were kept in situ. The most common complication was hematuria (13, 8.8%), followed by urinary tract infection (11, 7.5%) and pain (8, 5.4%). The volume of hydronephrosis (67.9 ± 34.9 VS 34.9 ± 51.1 cm³, P = 0.0001), serum creatinine level (103.0 ± 54.5 VS 93.8 ± 45.1 μmol/L, P = 0.034) and blood urea nitrogen level (6.6 ± 6.7 VS 5.4 ± 2.4 mmol/L, P = 0.032) decreased significantly at last follow up when compared with baseline. Stricture of the distal ureter was an independent risk factor for stent failure (HR 1.77, 95% CI 1.15, 2.73, P = 0.009).

CONCLUSIONS

URS was found to be safe and effective for ureteral strictures with a limited complications and good long-term results. For those who are not suitable for surgical reconstruction, the URS is an alternative management.

Palliative radiation treatment used for multiple purposes in a single irradiation field

In this case report, radiation therapy was performed for bilateral hydronephrosis developed during multiple bone metastases of breast cancer and ileus due to peritoneal dissemination. The patient's preirradiation creatinine level was 8.2 mg/dL, which decreased by the fourth day after starting irradiation therapy. Creatinine level ultimately decreased to 0.6 mg/dL. Pain due to lumbar spine metastasis alleviated and ileus was resolved, allowing the patient to live at home for approximately 5 weeks. The effect of radiotherapy for bilateral hydronephrosis and gastrointestinal obstruction was rapid and good. Palliative radiation treatment can be used for multiple purposes, and in the present patient, we were able to prolong the vital prognosis.

Placement of Resonance Stent for Malignant or Benign Ureteral Obstruction

The aim of this article is to illustrate a step-by-step guide to placement of Resonance^® metallic ureteral stent (Cook Medical, Bloomington, IN) for management of malignant or benign ureteral obstruction. In this article, the steps of operating room setup, patient positioning, gaining access to the upper urinary tract, and endoscopic and fluoroscopic placement of a Resonance ureteral stent are described.

New perspectives on angiotensin-converting enzyme 2 and its related diseases

Since the worldwide outbreak of coronavirus disease 2019, angiotensin-converting enzyme 2 (ACE2) has received widespread attention as the cell receptor of the severe acute respiratory syndrome coronavirus 2 virus. At the same time, as a key enzyme in the renin-angiotensin-system, ACE2 is considered to be an endogenous negative regulator of vasoconstriction, proliferation, fibrosis, and proinflammation caused by the ACE-angiotensin II-angiotensin type 1 receptor axis. ACE2 is now implicated as being closely connected to diabetes, cardiovascular, kidney, and lung diseases, and so on. This review covers the available information on the host factors regulating ACE2 and discusses its role in a variety of pathophysiological conditions in animal models and humans.

A systematic review of long-duration stents for ureteral stricture: which one to choose?

OBJECTIVE

To define which long-term stent would work best in malignant ureteral obstruction (MUO) and benign ureteral obstruction (BUO), focusing on their mechanisms of action, price and insertion approach.

METHODS

A systematic review was developed using the MEDLINE and Scopus databases and in accordance with the PRISMA checklist. There were no language restrictions for the search. Studies describing the use of metallic ureteric stents for MUO and for BUO in humans were included.

RESULTS

We analyzed five types of metallic stents (35 papers) and also the experience with the tumor and extra-anatomical stents. The Resonance, Memokath and Allium ureteral stents were found to be useful in BUO and MUO. The Uventa stent performed well in chronic ureteral obstruction. The Detour bypass stent was a recommended option in those patients who had complete obstruction of the ureter and were unfit for reconstructive surgery. There was no difference with regard to the insertion technique and both antegrade and retrograde approaches were equally successful. Although tumor stents showed a good performance, there were very few published studies on it.

CONCLUSION

Metallic stents are a suitable option for MUO and BUO. When compared to standard double J stents, although they are relatively high priced, they show a financial benefit in the long-term. The Detour bypass stent seems to be an effective alternative for complete ureteral obstruction or patients unfit for surgery. Further prospective randomized studies should be done on the effectiveness of tumor stents versus metallic stents.

Ureteroiliac artery fistula caused by full-length metallic ureteral stenting in a malignant ureteral obstruction: a case report

Background

The metallic stent is a new device for relieving the urinary tract in patients with malignant ureteral obstruction with short life expectancy and has been used frequently worldwide for its efficacy and safety. A ureteroarterial fistula with indwelling ureteral stent is rare but highly fatal, and there are several reports of ureteroarterial fistula treated by conventional polymer stents, although there are no reports on metallic stents. To our knowledge, this paper describes the first case of a ureteroiliac artery fistula caused by a full-length metallic ureteral stent in malignant ureteral obstruction.

Case presentation

Our patient was a 57-year-old Asian woman with a history of locally advanced cervical cancer who underwent abdominal total hysterectomy and chemoradiotherapy. She was diagnosed with right hydronephrosis and hydroureter secondary to upper ureteral obstruction because of retroperitoneal lymph node metastasis. A urinary tract obstruction after placement of 12 months of polymer stent followed by 18 months of metallic stent was relieved, consequently resulting in intermittent gross hematuria with bladder tamponade and anemia. Contrast-enhanced computed tomography could not reveal a ureteroarterial fistula; however, retrograde pyelography emphasized the existence of a ureteroiliac artery fistula. The patient underwent successful endovascular heparin-bonded stent graft placement, and her gross hematuria disappeared thereafter.

Conclusion

The metallic stent is a useful device for patients with malignant ureteral obstruction with a short life expectancy, although it may impose a higher pressure on the extraureteral tissue than conventional polymer stents due to its properties and may cause a ureteroarterial fistula. The narrowing of the external iliac artery diameter visualized by computed tomography may be helpful for predicting ureteroarterial fistulas.

ACR Appropriateness Criteria® Radiologic Management of Urinary Tract Obstruction

Acute obstructive uropathy is a medical emergency, which often is accompanied by acute renal failure or sepsis. Treatment options to resolve the acute obstructive process include conservative medical management, retrograde ureteral stenting, or placement of percutaneous nephrostomy or nephroureteral catheters. It is important to understand the various treatment options in differing clinical scenarios in order to guide appropriate consultation. Prompt attention to the underlying obstructive process is often imperative to avoid further deterioration of the patient's clinical status. A summary of the data and most up-to-date clinical trials regarding treatment options for urinary tract obstruction is outlined in this publication. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

The resonance® metallic ureteral stent in the treatment of malignant ureteral obstruction: a prospective observational study

Background

To study the outcomes and experiences of using metallic stents in treating patients with malignant ureteral obstruction (MUO), we examined the effects of metallic ureteral stenting using the Cook Resonance® stent in the treatment of MUO.

Methods

All patients who had a Resonance metallic stent inserted between April 2015 and March 2018 at one of multiple facilities were prospectively observed with a 1-year follow-up. The primary outcome was the patency rate of the metallic ureteral stent. The secondary outcomes included the complications (e.g., infection and fever).

Results

Although stent insertion was attempted in 50 patients, the stent could not be inserted as a ureteral stent in three patients due to severe ureteral stricture, and one ureteral cancer patient was excluded from the analysis. The remaining 46 patients’ median age was 67 years (range 28–85 years) (16 males, 30 females). Twenty-four patients died during the study; their median survival time was 226 days. The median follow-up period for the censored patients was 355 days (range 16–372 days), and just seven patients were still alive without Resonance failure > 1 year later. The women’s IPSS scores tended to be lower than those of the men. Regarding the OABSS score, although the women’s total score tended to be low, the difference between the men’s and women’s scores was nonsignificant. The bacteria detected from urine culture after stent insertion were more gram-positive than gram-negative.

Conclusion

Metallic ureteric stenting using the Resonance stent is safe and effective for treating MUO. Subjective symptoms were relatively less in the female patients.

Tandem Resonance metallic double-J ureteral stents in a single ureter for salvage management of chronic ureteral obstruction

For chronic malignant and benign ureteral obstruction, the metal construction of the Resonance ureteral stent has been developed to maintain ureteral patency for up to 12 months, obviating the need for the frequent exchange required for conventional plastic ureteral stents. We report our experience placing tandem Resonance stents (TRS) in a single ureter of patients who failed management with a single Resonance stent. A retrospective review of patients who had TRS for management of ureteral obstruction between February 2014 and May 2017 was performed. Seven renal units from four patients with a median age of 62 years were managed with TRS. All but one renal unit was successfully managed with TRS initially. Hydronephrosis resolved in 80% of renal units at a median of 33 days, and creatinine reached its nadir a median of 38 days after placement, with a median improvement of 0.68 ng/mL. However, the median length of management with TRS was only 123.5 days with one exchange, and there was an overall success rate of 28.5% at 1 year. TRS placement is a feasible option for short-term management in a challenging population that would like to avoid nephrostomy and has failed other modalities.

Malignant ureteral obstruction: experience and comparative analysis of metallic versus ordinary polymer ureteral stents

BACKGROUND

To study the outcome and experience of using metallic stents in treating patients with malignant ureteral obstruction (MUO).

METHODS

Seventy-six patients with MUO were assigned to the metallic stent group (MSG) or the ordinary polymer stent group (OPSG) according to the different materials. The success rate of the operation, duration of operation, patency rate serum creatinine values ,postoperative complications and QOL scores were compared between the two groups.

RESULTS

In the OPSG and MSG, the success rates of the operation were 95.5% and 96.9%, respectively, and the durations of the operation were 20.6 ± 2.2 min and 50.9 ± 10.3 min (P < 0.01), respectively. There was no significant difference between the groups in serum creatinine values at 3 days after the operation (P > 0.05); however, the creatinine values at 3 days after the operation decreased significantly compared with those before the operation (P < 0.01). In the OPSG, there was no significant difference in creatinine values between 3 days and 6 months after operation, while the creatinine values 1 year after operation were increased significantly compared to those at 3 days after the operation (P < 0.05). In the MSG, there was no significant difference among creatinine values at different intervals (P > 0.05). The total rate of post-procedural complication was lower in the MSG than that in the OPSG(P < 0.05). There was no significant difference in the QOL score between the two groups before the operation (P > 0.05); however, the QOL scores at 6 months and 1 year after the operation were higher in the MSG than that in the OPSG(P < 0.05). In the MSG, there was no significant difference in the QOL score between preoperation and 6 months after surgery. Similarly, there was also no difference in the QOL score between 6 months after surgery and 1 year after surgery(P > 0.05). On the contrary, the differences of QOL score in the OPSG group were much significant between disparate time intervals (P < 0.05).

CONCLUSIONS

For patients with MUO who require long-term retention of the stent, metallic stents with longer indwelling time are superior to ordinary polymeric stents.

Application of metallic ureteral stents in gynecological malignancies: a literature review

Ureteral obstruction caused by extrinsic compression from advanced pelvic malignancies are not unusual in urology, with gynecological origin being the most common. As minimally invasive treatments for malignant ureteral obstruction (MUO), metallic ureteral stents have been promoted to provide long-lasting urinary patency and overcome the inherent limits of traditional double-J stents. In this review, we demonstrated three types of frequently used metal stents, including coiled stents, self-expendable stents and thermo-expendable stents. The Wallstent presented discrepant patency rates ranging from 6% to 100%, along with a high occlusion rate. The Memokath 051 stent showed satisfactory patency rates, often > 90%, but also a specific higher migration rate. The Resonance stent provided overall promising results with published success rates ranging from 20% to 100%, which on the whole remains relatively high. The long-term effectiveness rendered metal stents as viable options for managing MUO.

Gastrointestinal cancer and bilateral hydronephrosis resulted in a high risk of ureteral stent failure

Background

Urologists frequently encounter malignant ureteral obstruction (MUO) caused by advanced urological or non-urological malignant disease, but the treatment policy is unclear. The present study examined the risk factors for predicting ureteral stent failure in patients with MUO after ureteral stent insertion and the change in the renal function after retrograde ureteral stent insertion in cases of bilateral hydronephrosis.

Methods

A total of 39 patients who required ureteral stent placement for MUO at Yokohama City University Medical Center (Yokohama, Japan) between February 2007 and May 2016 were included in this study. The age, gender, type of cancer, hydronephrosis side, pre-stenting estimated glomerular filtration rate (eGFR), and eGFR increase were assessed as predictive factors for stent failure. Among these 39 patients, 25 showed bilateral hydronephrosis. Thirteen of these patients had bilateral ureteral stents placed, and the remaining 12 had a unilateral ureteral stent placed. The renal function and overall survival (OS) were analyzed between these two groups.

Results

Among all 39 patients, 9 (23.1%) had stent failure. A univariate analysis revealed that causative disease (gastrointestinal cancer vs. others; p = 0.045) and laterality of hydronephrosis (bilateral vs. unilateral; p = 0.05) were associated with stent failure. A multivariate analysis revealed that only age (hazard ratio, 0.938; 95% confidence interval, 0.883–0.996; p = 0.038) was associated with stent failure. A Kaplan-Meier analysis and log-rank test indicated that having a unilateral ureteral stent placed was not correlated with a lower OS rate than having bilateral ureteral stents placed (p = 0.563). Among patients with bilateral hydronephrosis, the increase in the eGFR of those who had bilateral ureteral stents placed was not significantly different from that of those who had a unilateral ureteral stent placed (p = 0.152).

Conclusions

We revealed that age > 60 years was helpful for predicting stent failure. MUO due to gastrointestinal cancer and bilateral hydronephrosis may be predictive of stent failure. These factors may help urologists decide the optimal time to perform early percutaneous nephrostomy. These findings suggest that patients with bilateral hydronephrosis do not necessarily need to have a ureteral stent placed into both sides of the hydronephrosis.

Application of resonance metallic stents for malignant ureteral obstruction

Purpose: To determine the effectiveness of the Resonance metallic stent in treating malignant ureteral obstruction (MUO) and clarify the risk factors that lead to stent failure. Material and methods: We retrospectively identified and analyzed the records of patients who had MUO and underwent placement of Resonance metallic stents from November 2014 to June 2017 in our hospital. Stent failure was defined as unexpected interventions including stent exchange, need of percutaneous nephrostomies (PCN) or ureterocutaneostomy. Results: A total of 22 stents were placed in 14 patients with MUO. The median follow-up was 145 days (4.8 months) and the maximum duration of stenting was 21.3 months. The technique success rate was 100%. Two patients experienced early postoperative increasing creatinine with oliguria but only one of them failed to achieve primary patency. The overall success rate was 90% (9/10). Conclusion: Resonance metallic stent is a safe and effective treatment for MUO and can maintain durable patency over 12 months. Preoperative urinary tract infection (UTI) and tumor invasion into the bladder are considered as risk factors of stent blockage and failure. Early postoperative elevated creatinine oliguria, suggestive with intrarenal and prerenal disease, should not be deemed to be stent failure.

Risk Factors for Primary Failure of Metallic Ureteral Stents: Experience from a Tertiary Center

Introduction: We provide primary patency rate of metallic ureteral stents in cancer patients and investigate the factors affecting primary patency. Methods: All cancer patients who had received metallic stents for malignant ureteral obstruction between July 2009 and November 2012 in our institute were included. No patients were excluded. Patient profiles, imaging studies, and laboratory data were collected. Patient profiles included age, gender, body height, body weight, body mass index, cancer types, treatment for cancer, response to cancer treatment, methods of stent insertion, and prior ordinary stents. Imaging studies included renal ultrasonography, antegrade pyelography, CT, and MRI. Laboratory data included urinalysis, urine culture, and serum creatinine. Complications were defined according to the Clavien-Dindo classification. Primary patency was defined as a complete resolution or downgrading of hydronephrosis shown by imaging studies or success in the removal of a preexisting nephrostomy tube; otherwise the procedure was considered a primary failure. The primary endpoint was the primary patency rate of the stents. The secondary endpoints were risk factors for primary stent failure. Results: A total of 124 stents were inserted into 96 patients with malignant ureteral obstruction. There were no grade 3/4 complications. The overall primary patency rate was 87.9% (109/124). In univariate analysis, antegrade insertion (OR = 24.15, p-value = 0.0086) and urinary tract cancer (OR = 4.18, p-value = 0.0164) were significantly associated with primary failure. Those with prior ordinary stents (OR = 0.20, p-value = 0.0158) or response to cancer treatment (OR = 0.25, p-value = 0.0228) were associated with stent patency. In multivariate analysis, antegrade insertion (OR = 22.04, p-value = 0.0041) and response to cancer treatment (OR = 0.15, p-value = 0.01081) remained significant factors. Conclusions: In this large cohort of cancer patients requiring urinary diversion to preserve renal function, several factors were associated with the success rate of metallic stents.

Retrograde pyelography predicts retrograde ureteral stenting failure and reduces unnecessary stenting trials in patients with advanced non-urological malignant ureteral obstruction

Objective

To evaluate predictive factors for retrograde ureteral stent failure in patients with non-urological malignant ureteral obstruction.

Materials and methods

Between 2005 and 2014, medical records of 284 malignant ureteral obstruction patients with 712 retrograde ureteral stent trials including 63 (22.2%) having bilateral malignant ureteral obstruction were retrospectively reviewed. Retrograde ureteral stent failure was defined as the inability to place ureteral stents by cystoscopy, recurrent stent obstruction within one month, or non-relief of azotemia within one week from the prior retrograde ureteral stent. The clinicopathological parameters and first retrograde pyelographic findings were analyzed to investigate the predictive factors for retrograde ureteral stent failure and conversion to percutaneous nephrostomy in multivariate analysis with a statistical significance of p < 0.05.

Results

Retrograde ureteral stent failure was detected in 14.1% of patients. The mean number of retrograde ureteral stent placements and indwelling duration of the ureteral stents were 2.5 ± 2.6 times and 8.6 ± 4.0 months, respectively. Multivariate analyses identified several specific RGP findings as significant predictive factors for retrograde ureteral stent failure (p < 0.05). The significant retrograde pyelographic findings included grade 4 hydronephrosis (hazard ratio 4.10, 95% confidence interval 1.39–12.09), irreversible ureteral kinking (hazard ratio 2.72, confidence interval 1.03–7.18), presence of bladder invasion (hazard ratio 4.78, confidence interval 1.81–12.63), and multiple lesions of ureteral stricture (hazard ratio 3.46, confidence interval 1.35–8.83) (p < 0.05).

Conclusion

Retrograde pyelography might prevent unnecessary and ineffective retrograde ureteral stent trials in patients with advanced non-urological malignant ureteral obstruction.

Tandem ureteral stents in the management of double-J stent dysfunction in gynecological malignancies

PURPOSE

The goal of this study was to determine the efficacy and safety of tandem ureteral stent placement in the management of malignant ureteral obstruction (MUO) refractory to single ureteral double-J stent drainage in women with gynecological malignancies.

MATERIALS AND METHODS

A retrospective study was performed on 14 women (mean age, 54.5±9.6 [SD] years; range: 38-70 years) who had tandem stent placement following failed single ureteral double-J stent placement from 2012 to 2017. Survival analyses were performed with Kaplan-Meier method.

RESULTS

Twenty-nine successful procedures were performed on 19 ureters (19 primary stent placement and 9 exchange procedures). Technical success of primary tandem stent placement was 95% (19/20 procedures). Mean follow-up was 180.1±173.7 (SD) days (range: 62-616 days). Median estimated survival of the patients was 118 days (Q1: 261, Q3: 95; range: 62-616 days). Primary stent failure rate was 25% and assisted stent failure rate was 21.4%. There was no significant difference among survival of patients with and without tandem stent failure. Mean estimated primary stent patency and assisted stent patency were 171.4±13.8 (SD) days and 409.9±59.8 (SD) days, respectively. Four patients underwent 1 to 3 stent exchanges. Median exchange time was 181 days (Q1: 151, Q3: 191, range: 141-214 days) and technical success rate was 100%. Grade 2 and 3 complication rates were 25% and 3.6%, respectively.

CONCLUSION

Tandem ureteral stent placement is a feasible, safe and effective procedure for the management of failed ureteral double-J stent placement in women with gynecological malignancies.

The resonance® metallic ureteric stent in the treatment of chronic ureteric obstruction: a safety and efficacy analysis from a contemporary clinical series

BACKGROUND

We evaluate the efficacy and safety of metallic ureteric stenting using the Cook Resonance® stent in the treatment of chronic ureteric obstruction of benign and malignant aetiology. Published experience of using this stent in this context is limited. We add to the body of literature on this topic.

METHODS

All patients who had a Resonance® metallic stent inserted between April 2009 and November 2014 in our institution were identified from a prospectively maintained stent-database. Primary outcome was relief of ureteric obstruction, defined by successful clinical and radiological treatment of hydronephrosis/hydroureter. Secondary outcome measures included operative time, radiological exposure, total stent dwell time (defined as the cumulative time in months for which a Resonance® metallic stent was in situ), and early and late complications.

RESULTS

Twenty-one patients underwent 52 stent insertion episodes (SIE). Median age was 58 years (range 39-90). Stent insertion resulted in successful treatment of hydronephrosis/hydroureter in 96% (2 SIE resulted in failure to relieve ureteric obstruction). Median operative time was 21 min (range 12-90) Median radiation exposure was 815.3 cGy/cm2 (range 192.9-5366.3). Median stent dwell time was 19.5 months (range 6-52) in non-malignant and 12 months (range 2-48) in malignant ureteric obstruction. One stent migrated proximally during insertion and had to be retrieved using an antegrade approach. 5 patients re-admitted with haematuria: all resolved without intervention or blood transfusion. 3 episodes of post-operative urinary infection were recorded; all were successfully treated with oral antibiotics.

CONCLUSION

Metallic ureteric stenting using the Resonance® stent is safe and effective for treating ureteric obstruction from both malignant and benign causes. The success rate in our series is 96%.

Cost Analysis of Metallic Stents for Chronic Ureteral Obstruction: A Multicenter Study

INTRODUCTION

Metallic and polymer ureteral stents are used to manage chronic ureteral obstruction. In general, metallic stents are more costly than polymer stents but they are changed less frequently. We examined the overall costs of using these stent types at 2 institutions.

METHODS

We identified all patients in whom a metallic stent was placed at 2 academic institutions between July 2007 and July 2013. We calculated the average time to stent exchange or failure and the overall cost of metallic and polymer stent use. Costs included those associated with materials, operating room services, anesthesia and other expenses.

RESULTS

We identified 86 patients in whom a total of 230 metallic stents were placed. Time to stent failure or exchange of a metallic stent was 7.4 months. The per unit cost of a polymer stent and a metallic stent was $121 and $887, respectively. The average annual cost of unilateral and bilateral metallic stents was $7,859.43 and $9,296.37, respectively. For a unilateral polymer stent that was changed every 3 months the yearly cost was $16,342. For bilateral polymer stents that were changed every 3 months the cost was $16,826 per year. If unilateral and bilateral polymer stents were changed every 6 months, the costs were $8,171 and $8,413, respectively.

CONCLUSIONS

Our findings suggest that because metallic stents are changed less frequently than polymer stents, the annual expense associated with treating patients with chronic ureteral obstruction can be decreased by using metallic stents.

[Management of ureteral obstruction : Value of percutaneous nephrostomy and ureteral stents]

Ureteral obstruction represents a heterogeneous disease pattern and is treated by ureteral stenting or percutaneous nephrostomy (PCN) depending on the necessity. The benefits of urinary diversion with ureteral stenting or PCN in malignant ureteral obstruction (MUO) for patient survival are only moderate. No differences have been found between ureteral stenting and PCN in MUO with regard to median patient survival and complication rates. In cases of MUO there is currently no evidence that urinary diversion improves the quality of life. Alternative concepts of ureteral stenting, such as tandem ureteral stents, metallic ureteral stents or metal mesh ureteral stents have not yet shown clear benefits. In benign ureteral obstruction, prospective randomized studies have demonstrated comparable quality of life after PCN or ureteral stenting. The method of choice for urinary diversion is influenced by the recommendations, personal experience of the clinician and the availability of the method.

Predicting the failure of retrograde ureteral stent insertion for managing malignant ureteral obstruction in outpatients

Malignant ureteral obstruction (MUO) is an unpropitious sign that is commonly observed in patients with advanced incurable cancer. The present study aimed to evaluate predictive factors for the failure of retrograde ureteral stent insertion in the management of MUO in outpatients. A total of 164 patients with MUO were retrospectively assessed in this study. Clinical factors, including age, gender, type of malignancy, level of obstruction, cause of obstruction, pre-operative creatinine level, degree of hydronephrosis, condition of the contralateral ureter, prior radiotherapy, Eastern Cooperative Oncology Group performance status (ECOG PS), bladder wall invasion and technical failure, were recorded for each case. Univariate and multivariate logistic regression analyses were used to investigate the risk factors for predicting the failure of retrograde ureteral stent insertion. In total, 38 out of 164 patients experienced bilateral obstruction, therefore, a total of 202 ureteral units were available for data analysis. The rate of insertion failure in MUO was 34.65%. Multivariate analyses identified ECOG PS, degree of hydronephrosis and bladder wall invasion as independent predictors for insertion failure. Overall, the present study found that rate of retrograde ureteral stent insertion failure is high in outpatients with MUO, and that ECOG PS, degree of hydronephrosis and bladder invasion are potential independent predictors of insertion failure.

Laparoscopic ureterolysis with simultaneous ureteroscopy and percutaneous nephroscopy for treating complex ureteral obstruction after failed endoscopic intervention: A technical report

Objective

Complex ureteral obstruction is refractory to conventional urological intervention. This report describes a case of laparoscopic ureterolysis with simultaneous ureteroscopy and percutaneous nephroscopy for treating complex ureteral obstruction.

Methods

Right-side multiple ureteral stones and complicating ureteral obstruction failed an initial attempt of ureteroscopy lithotripsy with simultaneous percutaneous nephroscopy in a 23-year-old male. Laparoscopic ureterolysis with ureteroscopy and percutaneous nephroscopy was used simultaneously to dissect the periureteral adhesions with the patient placed in the Galdakao-modified supine Valdivia position. The ureter was incised to allow the insertion of a ureteral catheter through the twisted ureter, and a guide wire was advanced into the pelvis using ureteroscopy. A double-J stent was placed into the right-side ureter using antegrade percutaneous nephroscopy.

Results

The laparoendoscopic procedure lasted 330 min with an estimated bleeding volume of 100 mL. The patient underwent an uneventful postoperative course, and postoperative follow-up radiography confirmed good positioning of the double-J stent. The double-J stent was removed 3 months after operation. The patient remained asymptomatic within a 13-month follow-up period.

Conclusion

Laparoscopic ureterolysis with simultaneous ureteroscopy and percutaneous nephroscopy is an effective and safe treatment option for complex ureteral obstruction.

Malignant Ureteral Obstruction: Functional Duration of Metallic versus Polymeric Ureteral Stents

BACKGROUND

Ureteral obstruction caused by extrinsic compression is often associated with intra-abdominal cancers. Internal drainage with ureteral stents is typically the first-line therapy to relieve such obstructions. Novel designs of ureteral stents made of different materials have been invented to achieve better drainage. In this study, we described the functional outcomes of a Resonance metallic ureteral stent (Cook Medical, Bloomington, Indiana, USA) in patients with malignant ureteral obstruction and compare the functional duration of Resonance stents with regular polymeric stents in the same cohort.

METHODS

Cancer patients who received polymeric stents and subsequent Resonance stents for ureteral obstruction between July 2009 and November 2012 were included in a chart review. Stent failure was detected by clinical symptoms, imaging studies, and renal function tests. The functional durations of each stent were calculated, and possible factors affecting stent patency were investigated.

RESULTS

A total of 50 stents were successfully inserted into 50 ureteral units in 42 patients with malignant ureteral obstruction. There were 7 antegrade stents and 43 retrograde stents. There were no major complications. Stent-related symptoms were similar in both kinds of stents. After polymeric stents were replaced with Resonance metallic stents, hydronephrosis subsided or remained stable in 90% (45/50) of the ureteral units. Serum creatinine decreased or remained stable in 90% (38/42) of these patients. The Resonance stent exhibited a mean increase in functional duration of 4 months compared with the polymeric stents (p<0.0001), and 50% (25/50) of the Resonance stents exhibited a significant increase in functional duration (more than 3 months). Pre-operative serum creatinine < 2 was associated with a substantial increase in stent duration.

CONCLUSIONS

Resonance stents are effective and safe in relieving malignant ureteral obstructions after polymeric stents failure. Resonance stents can provide a longer functional duration than polymeric stents and should be offered as an option for internal drainage.

Stenting for malignant ureteral obstruction: Tandem, metal or metal-mesh stents

Extrinsic malignant compression of the ureter is not uncommon, often refractory to decompression with conventional polymeric ureteral stents, and frequently associated with limited survival. Alternative options for decompression include tandem ureteral stents, metallic stents and metal-mesh stents, though the preferred method remains controversial. We reviewed and updated our outcomes with tandem ureteral stents for malignant ureteral obstruction, and carried out a PubMed search using the terms "malignant ureteral obstruction," "tandem ureteral stents," "ipsilateral ureteral stents," "metal ureteral stent," "resonance stent," "silhouette stent" and "metal mesh stent." A comprehensive review of the literature and summary of outcomes is provided. The majority of studies encountered were retrospective with small sample sizes. The evidence is most robust for metal stents, whereas only limited data exists for tandem or metal-mesh stents. Metal and metal-mesh stents are considerably more expensive than tandem stenting, but the potential for less frequent stent exchanges makes them possibly cost-effective over time. Urinary tract infections have been associated with all stent types. A wide range of failure rates has been published for all types of stents, limiting direct comparison. Metal and metal-mesh stents show a high incidence of stent colic, migration and encrustation, whereas tandem stents appear to produce symptoms equivalent to single stents. Comparison is difficult given the limited evidence and heterogeneity of patients with malignant ureteral obstruction. It is clear that prospective, randomized studies are necessary to effectively scrutinize conventional, tandem, metallic ureteral and metal-mesh stents for their use in malignant ureteral obstruction.

Studying the Morbidity and Renal Function Outcome of Missed Internal Ureteral Stents: A Matched Pair Analysis

PURPOSE

To investigate the effect of missed internal ureteral stents (IUS) on renal function and to describe different modalities of management and associated morbidity.

PATIENTS AND METHODS

A retrospective study included patients with missed IUS (>1 year). The complications of missed IUS were categorized according to the forgotten, encrusted, calcified (FECal) grading system. The estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease (MDRD) equation at time of initial stent placement and time of stent removal. An age- and sex-matched group of patients who had IUS and had available follow-up for the same duration of the study group were used as a control.

RESULTS

A total of 46 missed IUS in 46 patients were included. Complicated stents were reported in 34 (73.9%) patients. FECal grade 1 was reported in 16 (57.2%) patients followed by grade 2 and 4 in 5 (17.8%) patients each. Retrograde removal, visual cystolitholapaxy, ureteroscopy with laser disintegration of encrustations and combined retrograde and antegrade approach have been used in 21, 5, 10, and 9 patients, respectively. In the missed IUS group, the mean±standard deviation (SD) eGFR has declined from 65.5±26.3 mL/min/1.73m(2) to 54.3±30 mL/min/1.73m(2) (P=0.001). While in the control group, the mean±SD eGFR has increased from 57.5±30 mL/min/1.73 m(2) to 66.7±27 mL/min/1.73 m(2) (P=0.001).

CONCLUSIONS

Missed IUS were associated with significant complications that necessitated more invasive intervention. In addition, IUS had a negative impact on renal function at time of removal.

Manual Replacement of Double J Stent Without Fluoroscopy (Double j stent replacement)

It is not always possible to replace a ureteric stent with a new one due to the fact that tumoral effect increases in ureter with time. We present our experience of manual replacement of double J stent without fluoroscopy. The data from 23 female patients who underwent double J stent replacement with a total of 110 times was retrospectively analyzed. The steps of technique are as follows: take out distal end of the double J stent through urethra to external urethral meatus cystoscopically, insert a 0.035-inch guide wire through double J stent to the renal pelvis or intra pelvicaliceal system, take out old double J stent over guide wire, slide new stent over guide wire and at external meatus level take out guide wire while gently sliding distal end of double J stent over guide wire into urethra. The mean age was 58.39 ± 9.21 years. Cervical, endometrial, and ovarian cancer were diagnosed in 16, 4, and 3 patients respectively. The mean follow-up and indwelling period were 13.8 ± 5.2, 3.8 ± 0.6 months, respectively. Increased pelvicaliceal dilatation, serum creatinine level, or renal parenchymal loss was not observed. Replacement of double J stents with this technique is easy and can be used successfully in distal ureteral obstructions.

The full metallic double-pigtail ureteral stent: Review of the clinical outcome and current status

The full metallic double-J ureteral stent (MS) was introduced as a method for providing long-term drainage in malignant ureteral obstruction. Experimental evaluation of the MS revealed that its mechanical features allow efficient drainage in difficult cases, which could not be managed by the insertion of a standard polymeric double-J stent. Clinical experience with the MS showed controversial results. Careful patient selection results in efficient long-term management of malignant ureteral obstruction. The use of the MS should also be considered in selected benign cases. Major complications are uncommon and the minor complications should not hinder its use. Experience in pediatric patients is limited and warrants additional study. The cost-effectiveness of the MS seems to be appropriate for long-term treatment. Further investigation with comparative clinical trials would document the outcome more extensively and establish the indications as well as the selection criteria for the MS.

A single-institution experience with metallic ureteral stents: a cost-effective method of managing deficiencies in ureteral drainage

INTRODUCTION

The limitations of traditional ureteral stents in patients with deficiencies in ureteral drainage have resulted in frequent stent exchanges. The implementation of metallic stents was introduced to improve the patency rates of patients with chronic upper urinary tract obstruction, obviating the need for frequent stent exchanges. We report our clinical experiences with the use of metallic ureteral stents in the management of poor ureteral drainage.

MATERIALS AND METHODS

Fifty patients underwent metallic ureteral stent placement from 2009 to 2012. Stent failure was defined as an unplanned stent exchange, need for nephrostomy tube placement, increasing hydronephrosis with stent in place, or an elevation in serum creatinine. Stent life was analyzed using the Kaplan-Meier methodology, as this was a time dependent continuous variable. A cost analysis was similarly conducted.

RESULTS

A total of 97 metallic stents were placed among our cohort of patients: 63 in cases of malignant obstruction, 33 in the setting of cutaneous ureterostomies, and 1 in an ileal conduit urinary diversion. Overall, stent failure occurred in 8.2% of the stents placed. Median stent life was 288.4 days (95% CI: 277.4-321.2 days). The estimated annual cost for traditional polymer stents (exchanged every 90 days) was $9,648-$13,128, while the estimated cost for metallic stents was $4,211-$5,313.

CONCLUSION

Our results indicate that metallic ureteral stent placement is a technically feasible procedure with minimal complications and is well tolerated among patients. Metallic stents can be left in situ for longer durations and provide a significant financial benefit when compared to traditional polymer stents.

Metallic ureteral stents in malignant ureteral obstruction: clinical factors predicting stent failure

PURPOSE

To provide clinical outcomes of the Resonance metallic ureteral stent in patients with malignant ureteral obstruction, as well as clinical factors predicting stent failure.

METHODS

Cancer patients who have received Resonance stents from July 2009 to March 2012 for ureteral obstruction were included for chart review. Stent failure was detected by clinical symptoms, image studies, and renal function tests. Survival analysis for stent duration was used to estimate patency rate and factors predicting stent failure.

RESULTS

A total of 117 stents were inserted successfully into 94 ureteral units in 79 patients. There were no major complications. These stents underwent survival analysis and proportional hazard regression. The median duration for the stents was 5.77 months. In multivariate analysis, age (P=0.043), preoperative serum creatinine level (P=0.0174), and cancer type (P=0.0494) were significant factors associated with stent failure. Cancer treatment before and after stent insertion had no effect on stent duration.

CONCLUSIONS

Resonance stents are effective and safe in relieving malignant ureteral obstructions. Old age and high serum creatinine level are predictors for stent failure. Stents in patients with lower gastrointestinal cancers have longer functional duration.

Tandem ureteral stents for the decompression of malignant and benign obstructive uropathy

PURPOSE

To evaluate the utility of two ipsilateral ureteral stents placed for benign and malignant ureteral obstruction.

METHODS

We performed a retrospective analysis of all cases of tandem ureteral stent (TUS) insertion at our institution from July 2007 through January 2013. Student t, Fisher exact, and log-rank test were used.

RESULTS

TUS insertion or exchange was performed in 187 cases. There were 66 patients (75 renal units) who underwent successful TUS insertion. Malignant ureteral obstruction (MUO) was the cause for obstruction in 39 renal units (34 patients) vs benign ureteral obstruction (BUO) in 36 renal units (32 patients). Four patients with BUO and 15 patients with MUO underwent stent exchanges at a mean 145 and 128 days, respectively. Serum creatinine levels were stable poststent placement (P=0.4). Degree of hydronephrosis improved (paired t test P<0.03) after stent placement for both benign and malignant cohorts. TUS placement was noted to fail (flank pain with worsening hydronephrosis or increasing creatinine level) in five renal units with MUO (12.8%) and none with BUO. Stent failure (either conventional or TUS) suggested worsening survival in those with MUO. Median survival for those with MUO and a history of stent failure (10 of 14 died, 71%) was 66 days compared with 432 days for those without a history of stent failure (8 of 20 died, 40%) (log-rank test P=0.007).

CONCLUSION

Our experience with the TUS, the largest to date, demonstrated that they are highly successful in both benign and malignant causes of obstruction, comparing favorably with metallic ureteral stents. Stent failure may be predictive for shorter survival.

Metallic ureteral stents in malignant ureteral obstruction: short-term results and radiological features predicting stent failure in patients with non-urological malignancies

PURPOSE

To provide short-term result of the metallic ureteral stent in patients with malignant ureteral obstruction and identify radiological findings predicting stent failure.

MATERIALS AND METHODS

The records of all patients with non-urological malignant diseases who have received metallic ureteral stents from July 2009 to March 2012 for ureteral obstruction were reviewed. Stent failure was detected by clinical symptoms and imaging studies. Survival analysis was used to estimate patency rates and factors predicting stent failure.

RESULTS

A total of 74 patients with 130 attempts of stent insertion were included. A total of 113 (86.9 %) stents were inserted successfully and 103 (91.2 %) achieved primary patency. After excluding cases without sufficient imaging data, 94 stents were included in the survival analysis. The median functional duration of the 94 stents was 6.2 months (range 3-476 days). Obstruction in abdominal ureter (p = 0.0279) and lymphatic metastasis around ureter (p = 0.0398) were risk factors for stent failure. The median functional durations of the stents for abdominal and pelvic obstructions were 4.5 months (range 3-263 days) and 6.5 months (range 4-476 days), respectively. The median durations of the stents with and without lymphatic metastasis were 5.3 months (range 4-398 days) and 7.8 months (range 31-476 days), respectively.

CONCLUSION

Metallic ureteral stents are effective and safe in relieving ureteral obstructions resulting from non-urological malignancies, and abdominal ureteral obstruction and lymphatic metastasis around ureter were associated with shorter functional duration.

Long-term results of metallic stents for malignant ureteral obstruction in advanced cervical carcinoma

PURPOSE

We present our experience with the use of metallic stents (Wallstents®) in the management of malignant ureteral obstruction to maintain renal function, thereby permitting the use of chemotherapeutic agents to treat the underlying malignancy.

PATIENTS AND METHODS

We retrospectively reviewed the records of 24 patients with ureteral obstruction secondary to advanced cervical carcinoma, stage T3b (n=10) and T4 (n=14), that was relieved by Wallstents. Nineteen patients needed bilateral and 5 needed unilateral Wallstents to relieve the obstruction. Fifty-six additional endourologic interventions were necessary to assure continued patency. Holmium laser ablation was used 14 times to manage tumor proliferation and ingrowth at the distal end of the stent. Thirty-two endostents, 4 extension, and 6 replacement stents were used to maintain patency of the ureter.

RESULTS

Nineteen of our 24 patients received between one and five chemotherapeutic cycles over 18 to 140 months. In five patients, placement of Wallstents did not achieve adequate decrease of the creatinine levels to allow treatment with chemotherapy. Thirteen of 24 Wallstents remained patent over 18 months, yielding a primary patency rate of 54%. Technical success rate of Wallstent placement was 100%. The overall mean primary and secondary patency rates of the stent were 16.5 and 52 months, respectively. For T3b and T4 patients, the mean primary patency rates were 20.6 and 13.6 months, respectively. Secondary patency for T3b patients was 73.9 months vs 36.4 months for T4 patients. There were no serious complications associated with Wallstent placement.

CONCLUSION

Wallstents offer a salutary solution to the problem of maintaining prolonged patency of ureters compromised by encasing neoplasms.

Resonance metallic stents do not effectively relieve extrinsic ureteral compression in pediatric patients

BACKGROUND AND PURPOSE

Use of metallic stents (Resonance) has been reported in the literature to be effective in relieving extrinsic obstruction in adults. Successful patency rates have been reported to be around 83.3%. The use of Resonance stents in children has not been reported. We present our experience with these stents in addressing extrinsic ureteral obstruction in the pediatric population.

PATIENTS AND METHODS

We identified two patients who underwent placement of Resonance stents for extrinsic compression at the Children's Hospital of the University of Pittsburgh Medical Center. The first patient is a 12-year-old girl with a solitary left kidney who had a diagnosis of pelvic rhabdomyosarcoma; she was treated with surgery followed by adjuvant chemoradiation. Two years post-treatment, worsening renal function secondary to ureteral strictures developed. The second patient is a 14-year-old girl with a history of Gardner syndrome. Recurrent desmoid tumors developed in her pelvis and retroperitoneum that led to right ureteral obstruction, necessitating a nephrostomy tube.

RESULTS

Both patients underwent successful technical placement of a Resonance stent. The time to failure for patient 1 was 3 months and for patient 2, 3 weeks. The first patient presented to the emergency department 3 months poststent in renal failure with a creatinine level of 13.7 mg/dL. This necessitated nephrostomy tube placement and hemodialysis. Ultimately, she needed an ileal ureter to preserve renal function. She is off hemodialysis and has a creatinine level of 2.2 mg/dL.The second patient, recurrent episodes of pyelonephritis, worsening hydronephrosis, and flank pain developed with just the Resonance stent in place. It was elected to remove the Resonance stent and replace the nephrostomy tube. She needed extensive ureterolysis, a right subtotal ureterectomy with a right to left ureteroureterostomy.

CONCLUSION

We did not find the use of these stents to be effective in children. The time to failure was significantly shorter in children than those reported in the literature for adults.

Outcomes of metallic stents for malignant ureteral obstruction

PURPOSE

Malignant ureteral obstruction often necessitates chronic urinary diversion and is associated with high rates of failure with traditional ureteral stents. We evaluated the outcomes of a metallic stent placed for malignant ureteral obstruction and determined the impact of risk factors previously associated with increased failure rates of traditional stents.

MATERIALS AND METHODS

Patients undergoing placement of the metallic Resonance® stent for malignant ureteral obstruction at an academic referral center were identified retrospectively. Stent failure was defined as unplanned stent exchange or nephrostomy tube placement for signs or symptoms of recurrent ureteral obstruction (recurrent hydroureteronephrosis or increasing creatinine). Predictors of time to stent failure were assessed using Cox regression.

RESULTS

A total of 37 stents were placed in 25 patients with malignant ureteral obstruction. Of these stents 12 (35%) were identified to fail. Progressive hydroureteronephrosis and increasing creatinine were the most common signs of stent failure. Three failed stents had migrated distally and no stents required removal for recurrent infection. Patients with evidence of prostate cancer invading the bladder at stent placement were found to have a significantly increased risk of failure (HR 6.50, 95% CI 1.45-29.20, p = 0.015). Notably symptomatic subcapsular hematomas were identified in 3 patients after metallic stent placement.

CONCLUSIONS

Failure rates with a metallic stent are similar to those historically observed with traditional polyurethane based stents in malignant ureteral obstruction. The invasion of prostate cancer in the bladder significantly increases the risk of failure. Patients should be counseled and observed for subcapsular hematoma formation with this device.

New metallic ureteral stents: improved tensile strength and resistance to extrinsic compression

BACKGROUND AND PURPOSE

Extrinsic ureteral compression challenges a ureteral stent's ability to facilitate urinary drainage and to protect the kidney. Our purpose was to evaluate the performance of new metallic coil-based ureteral stents in terms of tensile strength and radial compression force.

MATERIALS AND METHODS

Three stent designs tested from Prosurg Inc included Passage 7.0F, Snake 6.0F, and Snake 7.0F with the straight section covered with a biocompatible polymer tubing. A MTS Microbionix Testing System using Testworks II software, vibration isolation table, and a 5-N load cell were used to measure tensile and compressive strength. Stents were placed in hydraulic grips and stretched at a rate of 5 mm/s for 1 second under uniaxial tension. Extrinsic compression was exerted in 0.1-mm increments to maximum compression. The Young Modulus, E, was calculated from each trial using engineering stress. Data were analyzed using Mann-Whitney and t tests.

RESULTS

The Passage, Snake 6F, and Snake 7F stents had tensile strengths of 27±3, 5±0.1, and 73±26 kPa, respectively. Mann-Whitney tests show statistically significant difference between stents (P<0.05). Elastic modulus needed to cause extrinsic compression was highest for Snake 6F (145,842±14332 Pa) compared with that of Passage (124,999±3182 Pa) and Snake 7F (126,132±19316 Pa), (P<0.05).

CONCLUSION

The Snake 6F stent had the lowest tensile strength and was least resistant to extrinsic compression. The Snake 7F had the highest tensile strength and was most resistant to extrinsic compression. All three stents are more resistant to extrinsic compression than the Applied Silhouette or Cook Resonance, yet have lower tensile strengths.

Updates on the use of ureteral stents: focus on the Resonance(®) stent

The Resonance(®) metallic ureteral stent is one of the latest additions to the urologist's armamentarium in managing ureteral obstruction. One advantage of this stent over traditional polymer-based stents is resistance to encrustation with stone material, which allows longer dwell times and less frequent exchange procedures. Although exchanging a metallic stent is slightly more complicated than exchanging a polymer stent, the fluoroscopic techniques required are familiar to most urologists. The Resonance stent is also more resistant to compression by external forces, potentially allowing greater applicability in patients with metastatic cancer. Furthermore, the use of this stent in patients with benign ureteral obstruction is shown to be associated with significant cost reduction. Clinical studies on the use of this stent are accumulating and the results are mixed, although Level 1 evidence is lacking. In this article we present a comprehensive review of the available literature on the Resonance metallic ureteral stent.