Stented Ureter Research Articles

Technical refinement for third kidney transplantation

To overcome the technical difficulties of a third renal transplantation, we developed a refined technique. After native ureteral stenting, the subhepatic retroperitoneum was approached by way of a midline incision. The renal vein was sewn to the vena cava, the artery to the common iliac artery, and the ureter to the native stented ureter.

Application of Paclitaxel-Eluting Metal Mesh Stents within the Pig Ureter: An Experimental Study

ObjectiveThe purpose of the present study is to compare the standard bare metal stents (BMS) with the Paclitaxel-Drug Eluting Stent (DES) in the ureter of a pig model. Materials and methodsWe report on an experimental study with ten female pigs weighing between 25 and 30kg. The stents were randomly placed in either the right or left ureter in each of 10 study animals, for a total of 20 stented ureters. Ten ureters were stented with an R-Stent (Orbus Medical Technologies, Hoevelaken Netherlands), and ten with a Paclitaxel-Eluting Coronary Stent (Boston Scientific, Natick, MA, USA). Patency was measured by radiograph of the nephrostomy tract, intravenous urography and virtual endoscopy at 24hours and 21 days after the initial procedure, respectively. ResultsFree flow of urine through the stents into the bladder was documented in all stented ureters 24hours after stent insertion by radiograph of the nephrostomy tract. At the 21 day follow-up examination, 5 R-Stents were found to be completely occluded and two partially stenosed, whereas no occluded stent was detected in the Paclitaxel-DES group. Pathology examination of the stents at 21 days follow-up showed that the obstructed R-Stents generated severe inflammation with metaplasia of the urothelium. The Paclitaxel-Eluting MS generated a mild inflammatory response within the ureteral lumen at the site of the stent, without hindering ureteral patency. R-stents proved to develop more hyperplasia compared to the Paclitaxel-Eluting MS. ConclusionsPaclitaxel-DES, when compared with the standard R- Stent BMS, generated less inflammation and/or hyperplasia of the surrounding tissues, thus maintaining ureteral patency. Long-term animal trials are required to further validate our results.

Flow dynamics in a stented ureter

Flow dynamics in a stented ureter

Ureteral Metal Stents: A Tale or a Tool?

There are four types of ureteral metal stents: self expandable, balloon expandable, covered, and thermoexpandable shape-memory. Insertion of metal stents requires expertise with transurethral and percutaneous techniques. The stricture is traversed with the aid of a guidewire via a percutaneous nephrostomy, and the stenotic segment is dilated using a high-pressure balloon catheter. The stent is then inserted over the guidewire, such that the upper end bypasses the obstruction by at least 3 to 4 cm, while the lower end extends intravesically for 0.5 to 1 cm from the ureteral orifice. If necessary, two or more stents are placed in sequence, overlapping by at least 2 to 3 cm. Metal stents were initially used for the relief of end-stage malignant disease, and their role in the treatment of benign ureteral strictures is still undefined. Patients often complain of abdominal discomfort and mild pain after stent insertion, which soon resolve spontaneously. Hematuria usually stops after a few days and does not necessitate any treatment. Mild urothelial hyperplasia in the stent lumen is common but usually regresses after 4 to 6 weeks. Many authors suggest the use of a double-pigtail catheter for the first 4 to 6 weeks to avoid narrowing of the ureteral lumen. The influence of stents on ureteral peristalsis is a major but poorly documented issue. Encrustation is a significant problem that needs to be addressed. The characteristics of both the patient and the stent influence its likelihood. Migration of coated metal stents was seen in 81% of patients at our center. Virtual endoscopy has recently been introduced as a tool for the follow-up of patients with stented ureters. Further design development is necessary to obtain the ideal ureteral metal stent. In a recent study in female pigs, paclitaxel-eluting metal stents engendered less inflammation and hyperplasia of the surrounding tissues.

Phase I Trial of a Temporary Ureteral Drainage Stent

The temporary ureteral drainage stent (TUDS; Boston Scientific/Microvasive, Natick, MA) is a biodegradable device that is designed to maintain patency for 48 hours with gradual softening and spontaneous expulsion thereafter. We evaluated the durability, patency, and safety of TUDS in a Phase I clinical trial. Eighteen stone patients requiring sequential percutaneous nephrolithotomies (PNL) for complex stone disease underwent antegrade TUDS placement following initial percutaneous treatment. Nineteen devices were placed in 21 attempts, with one patient undergoing bilateral TUDS placement. Day 2 nephrostograms were performed to allow assessment of stent status and to demonstrate antegrade flow. Stents were removed at the time of the secondary PNL (day 2 or 3). No complications occurred during TUDS placement. On day 2, 1 stent had passed into the bladder. Eleven stents were completely intact, with seven others partially intact. Day 2 ureteral patency was demonstrated in all 19 stented ureters. Eighteen TUDS were removed completely during the secondary PNL with one incident of partial retention. All stent material had passed out of the body in all patients by 1 month. No adverse events were attributable to the TUDS. The TUDS appears to facilitate ureteral drainage for at least 48 hours after placement. Although occasional stent tail detachments were noted, these did not interfere with device function. The safety profile of TUDS was favorable, with no complications attributable to the device itself. A larger prospective clinical study in patients receiving TUDS placed retrograde after uncomplicated ureteroscopic manipulation appears appropriate on the basis of these initial findings.

Ureteral metallic stents: application of virtual endoscopy for ureteral patency control.

In the present study we have applied virtual endoscopy (VE) in patients with ureteral metallic stents as a follow-up tool study especially in the need to define ureteral patency. We performed the suggested technique in 6 patients with malignant ureteral obstruction treated successfully by placement of Wallstent intraureteral metallic stents, and correlated the results with antegrade nephrostomography 48 hours after initial stent placement. In 2 patients restenosis was observed, and in the remaining 4 patients the stented ureters remained patent during the follow up evaluation. VE and antegrade nephrostomography, were concurrent as to their findings. Moreover, VE proceeds beyond the stenotic segment, allowing visualization of the ureteral lumen both cephalad and caudal to the point of obstruction. VE is providing indeed a more accurate, direct and dynamic approach in the evaluation of a strictured ureteral lumen within the metallic stent.

Impact on ureteral peristalsis in a stented ureter. An experimental study in the pig.

Peristalsis was examined in ten pigs with stented ureters. In five of the animals, the stents were inserted 6-8 weeks before examination, which was performed using a 3.5 Ch catheter equipped with thin copper wires in two sites 10 cm apart. This set-up enabled an analysis of the frequency, direction and velocity of the peristaltic waves to be made. When diuresis was gradually raised, the frequency and velocity of the contractions usually increased in normal ureters, whereas we observed a decline in both of these parameters. There was a statistically significant difference in the lower frequency in the long-term stented animals. Retrograde peristalsis, aberrant waves and incomplete contractions were common in the ureters after prolonged stenting, and urine flow was greater around than through the stent. Our results suggest that the flow of urine is obstructed by a ureteral stent, and they support clinical data showing that such devices prolong the time it takes for a stone to pass to the bladder.

FLOW CHARACTERISTICS OF 3 UNIQUE URETERAL STENTS:: INVESTIGATION OF A POISEUILLE FLOW PATTERN

The pattern of flow in the stented ureter (intraluminal and/or extra luminal) has only been defined for the standard pigtail stent. No data are available on stent flow for any specialty stents. To our knowledge we present the first investigation characterizing the type of flow through a stent (Poiseuille versus nonPoiseuille flow). Flow was measured in an unstented ureter, a standard 7Fr double pigtail stent and the 7/3Fr Tail stent, 7Fr Spirastent and 14/7Fr endopyelotomy stent using a previously developed stent flow model. In vitro pressure flow studies were also done in nonfenestrated 14/7Fr, Tail and standard 7Fr stents. These stents were infused at a constant flow rate of 2 to 10 ml. per minute with monitoring of the corresponding pressure gradients. Resistance to flow was determined for these stents using pressure flow plots and Poiseuille's law. In vivo the 7Fr pigtail, 14/7Fr endopyelotomy and 7/3Fr Tail stents had statistically similar flow rates. Flow through each of these stents exceeded the flow through an unstented ureter. The Spirastent had the least flow in all categories tested. There was no correlation of Poiseuille flow parameters measured in vitro for nonfenestrated stents with in vivo stent flow. In stented ureters fluid drains through and around the stent regardless of its design. The flow characteristics of these 3 specialty stents were not predictable according to lumen or stent size. In vitro Poiseuille's flow did not correlate with in vivo stent flow.

THE MORPHOLOGICAL, IN SITU EFFECTS OF A SELF-REINFORCED BIOABSORBABLE POLYLACTIDE (SR-PLA 96) URETERIC STENT; AN EXPERIMENTAL STUDY

The present study was done to evaluate the biocompatibility of a new biodegradable double helical spiral self-reinforced poly-L, D-lactide copolymer (L/D ratio 96/4, SR-PLA96) ureteric stent. In sixteen dogs, the right ureter was cut transversally, sutured and stented with a 50 mm. long SR-PLA 96 stent. In eight dogs, left ureter was similarly operated and stented with a double-J pigtail stent (C-Flex, Cook Urological Inc.), while eight remaining ureters served as plain controls. Urine was analyzed for signs of infection. The dogs were terminated at 6, 12 and 24 weeks postoperatively and the ureters dissected to find persistent SR-PLA 96 particles or local ureteric changes. Histologic samples were taken at three levels of dissected ureters in contact with the stent. C-Flex and SR-PLA 96 materials were well tolerated. Both of these induced only minimal ureteral wall edema, epithelial hyperplasia, epithelial destruction and inflammatory cell reaction. In SR-PLA 96 stented ureters the tissue reaction subsided after the degradation of the device. SR-PLA 96 spiral stent is regarded highly compatible and SR-PLA 96 might be a suitable material for a partial ureteric stent. Biodegradation of a SR-PLA 96 stent makes stent removal unnecessary.

URETEROILEAL ANASTOMOTIC STRICTURES: AN INNOVATIVE APPROACH WITH METALLIC STENTS

Purpose We report our experience with the use of self-expandable metallic stents to bypass anastomotic strictures after ureteroileal urinary diversion. Materials and Methods We evaluated 3 men and 1 woman with invasive bladder carcinoma who underwent radical cystectomy and ileal conduit urinary diversion. Ureteroenteric anastomotic strictures developed after a mean of 16 months. Self-expandable metallic stents were successfully placed (bilaterally in 2) comprising 6 stented ureters that bypassed strictures. Mean patient age was 64 years and mean followup was 12 months. Results No restenosis was observed in 3 patients during followup. The stricture recurred 1 month after stent placement in the remaining patient and additional intervention was necessary, consisting of placement of a totally coaxial overlapping metal stent. No sepsis or other complication was observed. One patient died of metastatic disease 12 months after stent placement. Conclusions We propose the use of metal stents as an adequate, safe and effective alternative treatment for anastomotic strictures after ureteroileal diversion.

Endostent: new device for ureteral strictures.

The results with the new Korth Endostent (manufactured by Rüsch), which was placed in 71 ureters after endopyelotomy, were compared with the results of conventional stenting in 183 ureters. Good or excellent results were seen in 79% of the Endostented ureters v 73% of the conventionally stented ureters. With conventional stents, results were better in primary than in secondary stenoses, whereas the reverse was true with the Endostent. The Endostent provided superior results in patients with third-degree hydronephrosis and in those with long scars. There was a striking reduction in the risk of infection (fever) in patients having an Endostent inserted (7% v 44%). The Endostent may also be indicated for permanent implantation in patients with strictures of ureterovesical anastomoses involving neobladders or allograft kidneys.

Ureteric drainage and peristalsis after stenting studied using colour Doppler ultrasound.

To study peristalsis and drainage of the stented ureter under normal physiological conditions. Fifteen non-obstructed patients with ureteric stents and 15 control subjects (i.e. 45 unstented ureters and 15 stented ureters) had ureteric jets and flow analysed using colour Doppler ultrasound (CDU). Cross-sectional and longitudinal studies were performed. Unstented ureters had forceful ureteric jets at a frequency of 0.5-4 jets/min per ureter. Asymmetry of frequency within subjects was common (1-3 jets/min). Some patent stented ureters had no recordable flow on CDU (four cases, three within the first week of stenting). In the remainder, three types of flow pattern were recorded; weak peristaltic jets were seen in a minority (four of 15), flow around the stent (periprosthetic flow) in 11 of 15 and flow through the lumen (luminal flow) in eight of 15. Jets were only seen late after stenting (> 2 months). The periprosthetic flow was mildly peristaltic in some patients and periprosthetic and jet flow increased relative to luminal flow during peak diuresis. Passive drainage (periprosthetic and luminal flow) is the principal mode of urine transport in the stented ureter throughout the diuretic response and particularly within a week of stenting. With longer duration of stenting (> 2 months) weak peristaltic activity and active ureteric transport became more evident, notably during peak diuresis. CDU is not reliable for diagnosing obstruction of the stented ureter.

Experimental study of Wallstent self-expandable metal stent in ureteral implantation.

In regard to the risk of stent obstruction, there are persistent controversies concerning the use of the Wallstent self-expandable metal stents in the ureter. Only a few clinical trials have been published to date, and, from a technical point of view, no success predictors have been identified. In an experimental study using a pig model, we have shown that neither the length of the stent (5 or 10 cm) nor an initial 1-month intubation had any influence on the outcome of the stents. Among the eight implantations studied (four 5-cm and four 10-cm stents), only one 5-cm stent was perfectly patent at 35 days. In all the remaining stents, after 35 or 90 days, constant failure was related to distal narrowing at the edge of the stent, with no difference between the 5- and 10-cm stents or between the intubated and the nonintubated stents. This distal narrowing, probably attributable to a functional discrepancy between an adynamic stented ureter and a normal underlying ureter, demands extreme caution in human applications when the ureter is normally peristaltic.

The effect of ureteric stenting on the function and morphology of long-term rat renal allografts.

In the development of a reliable model for chronic rejection in rat renal allografts, the effect of modifying the ureteric anastomosis was tested. Rats, tolerized by pretreatment with two donor blood transfusions under Cyclosporin A, received renal allografts with either sewn or stented ureter. Control groups received isografts or underwent uninephrectomy with insertion of ureteric stents. For the first 6 days after transplantation, serum creatinine and urea values were lower in allograft recipients with stented ureters than in the group with sewn ureters. The method of ureteric anastomosis did not affect the long-term incidence of abnormal function. Allograft morphology was extremely variable from minor to extensive tubular atrophy, interstitial fibrosis, glomerular hypertrophy, focal and segmental glomerulosclerosis as well as vascular changes. Glomerulosclerosis was absent in controls and increased with time in the allografts. Two hundred days after transplantation all allograft recipients with sewn ureters exhibited some glomerulosclerosis, in half of these kidneys more than 25% of glomeruli were affected. Only 33% recipients of allografts with stented ureters exhibited some glomerulosclerosis and less than 20% of glomeruli were affected. The stented ureteric anastomosis provides a reliable method, a reduction of the technical failure rate, a reduction of the incidence of hydronephrosis, allows more accurate assessment of early renal function and may be of importance in reducing the occurrence and prevalence of glomerulosclerosis in the long-term allografts.

Long-Term Effects of Ureteric Stent after Ureteric Dilation

Balloon dilation of the right ureterovesical junction (UVJ) and distal ureter to three times its normal caliber was performed in 12 pigs. A right double-J (D-J) stent was inserted after dilation in 6 pigs. Bilateral upper tract dynamics with different perfusion rates (0.5, 2 and 4ml. per minute) were recorded before dilation, immediately after dilation, and then 4 and 7 weeks after dilation. Immediate and late antegrade nephrostograms as well as suprapubic cystograms were taken. Grade 3 reflux occurred in 100% of animals at 7 weeks on the dilated, stented ureter and no reflux on the dilated, nonstented ureter. At 7 weeks on the dilated, stented side, significant growth (>100,000, colonies) of Pseudomonas species was noted in all animals. Creatinine clearance was significantly reduced on the dilated, stented side when compared to the dilated, nonstented side at 7 weeks. Histologic examination of the dilated, stented and dilated, nonstented ureters at 4 weeks revealed a segmental muscular defect with muscular regeneration starting from the edge of the defect, particularly in the innermost region. At 7 weeks, there was a more advanced, but similar, pattern of muscular regeneration in both groups. However, at 7 weeks, metaplastic changes of the ureter and chronic pyelonephritis were evident on the dilated, stented ureter. Electron microscopy showed that myofibroblasts played a major role in the healing process with new muscle formation. At 4 weeks, no significant morphologic difference was found between the dilated, stented and dilated, nonstented ureters. At 7 weeks, however, it appeared that the ureteric stent resulted in damage and deterioration of renal function without affecting muscular regeneration of the ureter. We conclude that the changes observed could be entirely due to the infection associated with the stent rather the stent itself.

Occlusive effect of metallic stents on canine ureters.

A three-part study, with successive modifications based on preceding results, was conducted to evaluate ureteral placement of metallic stents. Gianturco self-expanding (10 mm and 4 mm diameter) and balloon-expanded (4 mm diameter) metallic stents were placed in normal and stenotic canine ureters. No migration or ureteral perforation occurred during the follow-up of 10 mm stents. Varying degrees of hydronephrosis and hydroureter were found on all 1-week pyelograms. At 4 weeks, complete occlusion of the stented ureter was noted in all cases because of mucosal hyperplasia around the stent wires. To prevent this reaction, 4 mm self-expanding stents constructed of smaller wire that was uncoated or coated with either Teflon or poly-urethane were tested in five dogs. In all cases, results were similar to those obtained with the larger prostheses. Finally, 4 mm balloon-expanded stents were placed in a normal ureter of three dogs. In one dog, the stent migrated out of the ureter. No migration or ureteral perforation occurred in the two remaining dogs. In these animals, mucosal hyperplasia and complete ureteral occlusion occurred 6 and 8 weeks after placement. Therefore, ureteral placement of Gianturco self-expanding as well as balloon-expanded metallic stents leads to occlusion of the ureter instead of maintaining its patency. Stents, therefore, may be useful as ureteral occlusion devices.