Metallic Ureteral Stents Research Articles

Rationale and Feasibility Study of a Mechanical Model for the Testing of Material Fatigue in Metal Ureteral Stents

Stents are used abundantly to maintain ureteral patency. The majority are plastic tubes that adjust easily to upper urinary-tract motion. Recently, a coiled-wire lumenless stent was introduced (ZebraStent, Neo Medical, Munich, Germany) to facilitate expulsion of stone fragments after lithotripsy. Its metal core is composed of Nitinol, with the soft J ends being of titanium. The thin shape considerably increases the extraluminal space. The ZebraStent stretches the ureter and also provides a surface for the fragments to glide along. In our 18-month experience with the ZebraStent, two of them fractured along the shaft. We sought to learn whether this complication resulted from a defect in stent design or from material fatigue secondary to constant movement. Our model is powered by an electric motor that produces a constant displacement similar to stent movements in vivo. The whole ZebraStent is embedded in a 37 degrees C waterbath to simulate physiological conditions within the ureter. We used an average displacement of 16 mm. The average frequency of ventilatory-cycle simulation was 20 times that in vivo, allowing us to collect data in a shorter time. All 10 stents broke within the proximal Nitinol shaft at the equivalent of 4 to 6 months (125-179 days). Our preliminary results show that all stents break after the equivalent of 4 or more months. The fact that this occurs in the homogenous proximal Nitinol shaft rather than at the welding point between the shaft and the titanium curl implies that breakage is secondary to material fatigue and not design error. Extensive testing is under way to confirm material fatigue as the cause of breakage. We hope to determine a safe dwelling time for these stents, which at the moment should not exceed 3 months.

Initial Experience with the Resonance Metallic Stent for Antegrade Ureteric Stenting

We describe our initial experience with a new metallic ureteric stent which has been designed to provide long-term urinary drainage in patients with malignant ureteric strictures. The aim is to achieve longer primary patency rates than conventional polyurethane ureteric stents, where encrustation and compression by malignant masses limit primary patency. The Resonance metallic double-pigtail ureteric stent (Cook, Ireland) is constructed from coiled wire spirals of a corrosion-resistant alloy designed to minimize tissue in-growth and resist encrustation, and the manufacturer recommends interval stent change at 12 months. Seventeen Resonance stents were inserted via an antegrade approach into 15 patients between December 2004 and March 2006. The causes of ureteric obstruction were malignancies of the bladder (n = 4), colon (n = 3), gynecologic (n = 5), and others (n = 3). One patient had the stent changed after 12 months, and 3 patients had their stents changed at 6 months. These stents were draining adequately with minimal encrustation. Four patients are still alive with functioning stents in situ for 2-10 months. Seven patients died with functioning stents in place (follow-up periods of 1 week to 8 months). Three stents failed from the outset due to bulky pelvic malignancy resulting in high intravesical pressure, as occurs with conventional plastic stents. Our initial experience with the Resonance metallic ureteric stent indicates that it may provide adequate long-term urinary drainage (up to 12 months) in patients with malignant ureteric obstruction but without significantly bulky pelvic disease. This obviates the need for regular stent changes and would offer significant benefit for these patients with limited life expectancy.

Application of Self-Expandable Metal Stents for Ureteroileal Anastomotic Strictures: Long-Term Results

We report our long-term experience with the management of benign ureteroileal anastomotic strictures using self-expandable metal stents. A total of 16 male and 2 female patients with a mean+/-SD age of 72+/-7 years (range 66 to 78) with benign fibrotic strictures at the site of ureteroileal anastomosis underwent implantation of self-expandable metal stents with a nominal diameter of 6 to 8 mm. A total of 24 ureteroileal conduits were treated. The external nephrostomy tubes were removed after fluoroscopic validation of ureteral patency. Patients were followed with blood biochemistry, ultrasonography, urography and/or virtual endoscopy. Retrograde external-internal catheter insertion through the cutaneous stoma was performed in cases of recalcitrant stricture. The technical success rate of ureteroileal stricture crossing and stenting was 100% (24 of 24 cases). Mean followup was 21 months (range 7 to 50). The clinical success rate during the immediate post-stenting period was 70.8% (17 of 24 cases). The 1 and 4-year primary patency rates were 37.8% and 22.7%, respectively. Secondary interventions included repeat balloon dilation in 15 ureters, of which 8 also underwent subsequent coaxial stent placement. The 1 and 4-year secondary patency rates were 64.8% and 56.7%, respectively. Except in 2 patients who died external-internal Double-J catheters continued to be inserted retrograde in 6 ureteroileal conduits. They are periodically exchanged to prevent mucous inspissation and stent encrustation. Metal stents served as the definitive treatment for stricture in more than half of the cases, whereas in the remainder the stents allowed the uncomplicated and regular exchange of Double-J catheters in retrograde fashion. This combined, less invasive treatment for ureteroileal anastomotic strictures may help patients avoid surgical revision and preserve quality of life.

Self-Expanding Metallic Ureteral Stents for Treatment of Ureteral Stenosis After Kidney Transplantation

The incidence of post–renal transplantation ureteral stenosis ranges from 2%–12%. Because the role of self-expanding ureteral metallic stents for its tretment has been scarcely reported, the aim of this study was to evaluate the efficacy of Nitinol stents. Eleven ureteral stenoses in patients with chronic graft dysfunction (8 cases) or high surgical risk (3 cases) were treated by antegrade percutaneous implantation of Nitinol stents through a nephrostomy tract. The mean follow-up period was 48 ± 7 months (range, 3–85 months). The patency rate at the moment of return to dialysis, death, or last check-up was 73% (8/11). Three patients (27%) developed stent occlusion. Two patients were treated using a trans-stent double-J catheter and 1 patient using stent removal and pyeloureterostomy using the native ureter. The mean percentage decrease in serum creatinine (Cr) level after stent implantation was 41% (range, 14%–63%). Nitinol ureteral stent implantation is an effective alternative for the treatment of ureteral stenosis in patients with chronic graft dysfunction or high surgical risk.

Metallic Ureteral Stents versus Endoureterotomy as a Therapeutic Approach for Experimental Ureteral Stricture

To determine if the deployment of metallic ureteral stents in benign ureteral stricture is more effective than endoureterotomy. Twenty pigs were randomly divided in two groups to be treated with endoureterotomy or metallic stents. The internal ureteral diameter 2 cm distal to the ureteropelvic junction, histopathologic changes, ultrasonographic and fluoroscopic studies, urine culture, and serum urea and creatinine levels were analyzed during the phases of the study. The study was divided into three phases. The first included premodel documentation of normal urinary tract and laparoscopic ureteral stricture induction. In the second phase 1 month later, diagnosis and endoureteral treatment were carried out. Twelve weeks after stricture treatment, follow-up imaging studies and postmortem evaluation of all animals were performed. The success rates were 80% for endoureterotomy and 70% for metallic stent implantation. In all animals in the latter group, a ureteral hyperplasic reaction took place that affected the zone of stent implantation. One difference between the groups was the presence of urinary infection in 30% of animals in the endoureterotomy group and in no animals treated with metallic stents. Statistically significant differences in ureteral diameter between the first and second study phases were found within both groups (P < .0001), but not between groups (P = .021). Results from pathologic analysis revealed statistically significant differences between groups (P = .0029). The interaction among the distal end of the metallic stent, the urothelium, and peristalsis might be the origin of the failure of these devices. Although the deployment of metallic stents is attractive compared with other endourologic techniques like endoureterotomy in cases of benign strictures, certain problems must be resolved to prevent hyperplasia. Until then, this technique will not be a fully reliable therapeutic option for ureteral disorders.

BIOCOMPATIBILITY OF NITINOL AND STAINLESS STEEL IN THE BLADDER: AN EXPERIMENTAL STUDY

We tested the biocompatibility of nitinol, a nickel titanium alloy, and stainless steel (SS) as bladder implant materials. Rats received a nitinol implant, an SS implant or were sham controls. Two, 3, 6 and 8 weeks following implantation 24-hour voiding behavior studies were performed to investigate bladder irritation. All animals were sacrificed 8 weeks after implantation and a sample of urine was aspirated for culture. The bladders were examined by light microscopy and scanning electron microscopy (SEM). No visible encrustations or infections were noted in urine. Voiding frequency in the light period 6 weeks after implantation was significantly decreased in the 2 implant groups compared with sham controls. There were no other significant differences in frequency or mean volume per void in the light or dark periods at any time point. Light microscopy demonstrated similar implant tissue effects in all groups with little or no inflammation or fibrosis. Under SEM all implants showed a brittle, amorphous coating devoid of cells. The transition between the urothelium mucosa and the rod was smoother for SS than for nitinol, suggesting an affinity of SS for mucosa. In all nitinol rods discontinuity was present between the mucosa and rod. Nitinol and SS do not cause more irritation than the effects of surgery alone and the 2 materials seem to be biocompatible in the bladder. Nitinol may be more inert than SS based on SEM results.

V31 Renal autotransplantation: An alternative after metallic ureteral stent incrustation

V31 Renal autotransplantation: An alternative after metallic ureteral stent incrustation

Metallic ureteric stents: the current situation.

Metallic ureteric stents: the current situation.

Covered metallic ureteral stent in the management of malignant ureteral obstruction: preliminary results

Objectives. To evaluate the effectiveness of ureteral Dacron-covered metallic stents in the management of malignant ureteral obstruction. Methods. Covered metallic stents were placed unilaterally using a percutaneous approach in an antegrade fashion into nine ureters of 8 patients with bilateral malignant ureteral obstruction. The contralateral kidneys were drained by percutaneous nephrostomy in 7 patients. The primary diagnoses were rectal cancer in 5 patients and cervical, bladder, and prostate cancers in the remaining cases. Results. Covered metallic stents could be successfully placed in all patients. Only one of nine ureters was stented with a double J-stent. In a mean follow-up of 9 months (range 1 to 14), 7 of 8 patients died because of their primary disease. During the follow-up period, none of the stents were obstructed, displaced, or infected. Conclusions. Dacron-covered metallic stents appear to be successful in the treatment of patients with malignant ureteral obstruction. The preliminary outcome encourages and justifies the application of this drainage method.

NICKEL-TITANIUM SHAPE MEMORY ALLOY MEMOKATH 051 URETERAL STENT FOR MANAGING LONG-TERM URETERAL OBSTRUCTION: 4-YEAR EXPERIENCE

We present our 4-year experience with the thermo-expandable shape memory alloy Memokath 051 stent (Engineers and Doctors of Copenhagen, Copenhagen, Denmark) for managing long-term ureteral obstruction. We used a nickel-titanium shape memory alloy ureteral stent to treat 28 patients 29 to 86 years old (mean age 59.2). Ureteral obstruction was caused by malignancy in 18 cases and by recurrent benign disease in 10. A total of 37 stents were inserted from November 1996 to November 2000 using general anesthesia. Mean followup was 19.3 months (range 3 to 35). Upper tract decompression was achieved in all cases. Currently 15 stents are functional in 13 patients, while 8 patients died with a total of 13 functioning stents in place. In 7 patients 9 stents were removed for various reasons. There has been no radiological evidence of encrustation to date. No patient has been rehospitalized with stent related sepsis pain or hematuria, resulting in improved quality of life. This stent seems to provide a significant benefit over conventional Double-J (Medical Engineering Corp., New York, New York) and other metallic stents. Its remarkable thermal memory permits removal, a feature that until recently was not available in any other metallic ureteral stent. Durable and complication-free decompression of the upper tract can be achieved with the Memokath 051.

The self-expanding metallic ureteric stent in the long-term management of benign ureteric strictures.

To evaluate and assess the long-term complications of using the thermo-expandable, nickel-titanium alloy stent (Memokath 051, Engineers & Doctors A/S, Hornbaek, Denmark) for managing benign ureteric strictures. Over a 3-year period, 13 Memokath stents were inserted in 11 patients (mean age 58 years, range 35-85) with 12 lower ureteric strictures. The cause of the stricture was benign in all cases, i.e. radiation fibrosis in three, retroperitoneal fibrosis, ischaemic uretero-ileal anastomosis and scarring after ureteroscopy in two each, and diathermy damage, extraluminal endometriosis and stone passage in one each. Four stents were 9 F with proximal expansion to 17 F and the other nine used were 10.5 F with proximal expansion to 20 F. The patients were followed for a mean (range) of 18 (1.5-33) months. No complications or side-effects occurred with nine stents; four stents were removed at a mean (range) of 16.3 (4-33) months. Three of these had become encrusted, two of which had been placed in patients who had either a history of stone disease or recurrent urinary tract infection. The other stent had migrated. The Memokath stent appears to have a useful role in managing benign ureteric strictures, but it must be closely monitored in patients who are predisposed to encrustation.

Metallic ureteric stents: early experience.

To report our experience with metallic self-expanding stents in the palliative care of patients with ureteric obstruction caused by advanced pelvic malignancy. Seven patients (five men and two women, mean age 72.8 years, range 58-88) with ureteric obstruction caused by advanced pelvic malignancy were evaluated. Self-expanding metallic Memotherm stents (Angiomed, Karlsruhe, Germany) were deployed using an antegrade approach in all patients. Patients were followed for a mean (range) of 9 (4-13) months to assess renal function and survival. All seven patients had good palliation; their quality of life was improved and symptom such as loin pain were ameliorated. Renal function was preserved; the mean serum creatinine level before and after stenting was 636 and 263 mumol/L, respectively). The mean duration of stent patency was 9 months. Of the five patients who subsequently died, only two had recurrent renal failure, presumably caused by stent occlusion. The use of metallic stents in the palliative care of ureteric obstruction caused by advanced pelvic malignancy is a safe and effective treatment.