Coated v noncoated ureteral metal stents: an experimental model

Retrospective comparison of internally and externally covered retrievable stent placement for patients with benign urethral strictures caused by traumatic injury

OBJECTIVE

The purpose of this article is to compare the clinical effectiveness and complications of externally and internally covered stents for the treatment of benign urethral strictures.

MATERIALS AND METHODS

From July 2002 to June 2010, 59 retrievable self-expandable polytetrafluoroethylene-covered nitinol stents were placed in 33 men with benign urethral strictures. These included 34 internally covered stents placed in 18 patients (group I) and 25 externally covered stents in 15 patients (group E). Stents were routinely removed 4 months after placement from patients who experienced no complications. Complications, duration of stent placement, removal techniques, and maintained patency rates were compared in the two groups.

RESULTS

Twenty-eight complications (82.4%) occurred in 15 patients in group I, whereas 12 complications (48%) occurred in six patients in group E (p=0.005). Three (16.7%) patients in group I and nine (60%) in group E had their stents electively removed without complications (p=0.010). Stent migration was more frequent in group I (47.1%) than in group E (24.0%). No tissue ingrowth was detected in group E, whereas six cases of tissue ingrowth occurred in group I (p=0.034). The standard technique was used more frequently in group E (70.8%). The median stent indwelling period was significantly shorter in group I than in group E (51.5 vs 114 days; p=0.34).

CONCLUSION

Despite their relatively high complication rates, externally covered stents are more effective with fewer complications than internally covered stents in the treatment of benign urethral strictures.

Ni-Cr-Co alloy ureteral stent: scanning electron microscopy and elemental analysis characterization after long-term indwelling

We report the first preliminary study on metal-alloy ureteral stent after long indwelling times. The aim is to analyze by physical-chemical characterization of the stent after use and to evaluate the material performance in this human in vivo case study. Six Resonance metallic stents (Cook Ireland) were inserted in six patients for 6, 10, 11, 12, 24, and 36 months. The stents were then collected and studied by Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Spectroscopy (EDS), gaining information about the metal stent surface and the amount and nature of the formed encrustation. The stents were all draining adequately, despite the presence of the bacterial biofilm layer in all stents. This layer was more dense and compact as the indwelling time increased. Some slight precipitation of inorganic compounds, such as brushite and calcium oxalate was observed. No epithelial tissue in growth was recorded. These preliminary results with Resonance metallic ureteral stents suggest the feasibility of a long-term approach in patients with chronic ureteral obstruction. The durability of the metal stent, the lack of epithelial tissue ingrowths and limited pain or discomfort to patients were proven over long time periods. The long-term use of these stents is therefore feasible, avoiding the continuous exchange of the stent, decreasing hospital costs and increasing the quality of life of patients affected by malignant pelvic tumors.

Comparison of a new polytetrafluoroethylene-covered metallic stent to a noncovered stent in canine ureters

The aim of this study was to determine the feasibility of using a newly designed polytetrafluoroethylene (PTFE)-covered metallic stent in the ureter by comparing its effectiveness with that of the noncovered stent in a canine model. We placed 14 stents in the ureters of seven mongrel dogs that weighed 30-40 kg each. The covered and noncovered stents were deployed in the right and left ureters, respectively, of six dogs. In the seventh dog, a covered stent and a double-J catheter were inserted in the right ureter, and a covered stent only was inserted in the left ureter. The first six dogs were sacrificed at 5, 10, and 15 weeks after deployment of the stents (two for each follow-up period), and the seventh dog was sacrificed at 30 weeks. There was no migration or poor expansion of any of the stents observed on plain radiography. On intravenous pyelogram and retrograde pyelogram, all of the covered stents at each follow-up period had patent lumens at the stented segments without hydronephrosis, and the passage of contrast material through it was well preserved. The noncovered stents in the dogs sacrificed at 5 and 10 weeks and one of the two dogs sacrificed at 15 weeks showed near-complete occlusion of the stent lumen due to ingrowth of the soft tissue, and severe hydronephrosis was also noted. The noncovered stent in the other dog sacrificed at 15 weeks showed the passage of contrast material without hydronephrosis, but the lumen of the stent was still nearly occluded by the soft tissue. There was no evidence of hydronephrosis or passage disturbance of the contrast material in both ureters of the dog sacrificed at 30 weeks. We conclude that the newly designed PTFE-covered stent effectively prevented the luminal occlusion caused by urothelial hyperplasia compared to the near-total occlusion of the noncovered stents, and no migration of the covered stents was noted.

Malignant extrinsic ureteral obstruction: a survey of urologists and medical oncologists regarding treatment patterns and preferences

OBJECTIVES

To investigate and compare practice patterns regarding malignant extrinsic ureteral obstruction among urologists (GU) and oncologists (ONC).

METHODS

We invited members of the American Urological Association and the American Society of Clinical Oncologists to participate in a web-based survey. Participants gave recommendations in clinical scenarios, as well as opinions regarding use of ureteral stents and nephrostomy tubes (PCN).

RESULTS

The survey was randomly sent to 1500 GU and 1500 ONC, of whom 226 (15%) and 191 (12.4%) responded, respectively. The groups significantly varied in treatment preferences in all clinical scenarios. Regarding stent failure, ONC preferred PCN (79% versus GU 62%); GU (18% versus 5%) next preferred stent manipulation (eg, increase stent size, dual stents) (P <0.0001). The greatest risk of stents per GU was decreased quality of life (65% versus 13%), whereas ONC were most concerned about infection (43% versus 3%) (P <0.0001). The greatest risk of PCN per GU was dislodgement (48% versus 18%), whereas ONC were most concerned about infection (40% versus 8%) (P <0.0001).

CONCLUSIONS

Practice patterns vary significantly between GU and ONC in the treatment of malignant extrinsic ureteral obstruction. Further investigation and collaboration are necessary to determine which interventions are best for these patients and how to ensure consistency in their care.

Long-term results of permanent metallic stent implantation in the treatment of benign upper urinary tract occlusion

AIM

The management of complicated benign upper urinary tract occlusion is extremely challenging, especially in patients unable to undergo an open operative procedure. We report the long-term results of a permanent metallic stent for benign upper urinary tract occlusion.

METHODS

From October 1995 to December 1998, 13 patients (8 men and 5 women, with a mean age of 43 years) with benign upper tract occlusion have been treated by metallic stent implantation. All patients had a nephrostomy tube to relieve the obstruction and the average time of the nephrostomy tube stay was 27 months, ranging from 3 to 131 months. The average length of occlusion was 2.7 cm, ranging from 1 to 3.6 cm. Ultrasonography, urography, diuresis renography and urine culture were performed every 3 months after stent insertion. Ureteroscopy was done when needed.

RESULTS

The mean follow-up was 92 months (12-132 months). Ureteral patency was achieved in six patients and assisted patency with a Double-J stent was achieved in three patients. In two patients the kidney had to be removed because of progressive malfunction and in two patients the metal stent had to be extracted with the Holmium: YAG laser, burning it down due to the uncontrollable pyonephrosis. In three patients the ipsilateral flank pain recurred. One of these patients experienced urine leakage due to the initial nephrostomy tract: a ureteroscopy revealed a complete hyperplastic urothelial response. Proximal stone formations were found in 2 patients and all were removed by percutaneous nephrolithotomy (PCNL). No stent migration or fragmentation was observed.

CONCLUSION

The implantation of metal stent is a safe and effective treatment for benign upper urinary tract occlusion, and has satisfying long-term outcome in selected cases. A further investigation is needed for its impact on the urodynamics of upper urinary tract.

Case Report: Urothelial Hyperplasia Causing Recurrent Obstruction after Ureteral Metal Stent Placement in Treatment of Ureteroenteric Anastomotic Stricture

Initial experience utilizing metal stents in the treatment of ureteroenteric anastomotic strictures has yielded promising results. However, the long-term efficacy of metal stent placement remains unknown. Further, there is a paucity of literature to describe the technical considerations associated with the surgical management of obstruction after metal stent failure. We report the case of a 67-year-old man undergoing bilateral ureteral metal stent removal and ileal conduit creation following stent failure and recurrent obstruction.

A New SWL Titanium Stent (Zebra Stent®): Resistance to Shockwave Exposure

BACKGROUND AND PURPOSE

Recently, a new-concept lumen-less Teflon-coated double-J wire stent (Zebra stent) has been introduced to facilitate residual stone clearance, in particular after SWL. Its metal core expresses highly mismatched acoustic impedance. It was the aim of this study to exclude damage to the stent through shockwaves. Also, its Teflon coating should to some degree prevent encrustation, and stents removed from stone formers were examined for encrustation.

MATERIALS AND METHODS

Series of 2000 shockwaves of an average and a maximum energy were applied to defined areas of Zebra stents in a waterbath on a Siemens Multiline Lithotriptor. Stents were then examined for core and sheath damage by digital photography, scanning electron microscopy, and microradiography. In addition, two Zebra stents and one conventional double-J stent from two stone formers were assessed in the same way for damage and encrustation.

RESULTS

There was no damage whatsoever to either of the stents. Whereas there was considerable encrustation on the conventional double-J stent, there was none on the Zebra stents after 4 and 5 weeks in situ.

CONCLUSIONS

Zebra stents resist shockwaves to a maximum number and energy sufficiently to be applied safely under SWL. Whether they resist encrustation to a higher degree in the short term than conventional stents remains to be established.

Endoscopic Treatment of Ureteric Strictures: Acucise, Cold-Knife Endoureterotomy and Wall Stents as a Salvage Approach

OBJECTIVE

To evaluate the factors influencing the results of endoureterotomy using cold-knife and cutting balloon dilatation, and permanent ureteral wall stents in patients with benign ureteral strictures after different operations affecting the ureter.

MATERIALS AND METHODS

Over a 4-year period, in 18 patients, endoscopic cold-knife and Acucise endoureterotomies were performed in 13 and 7 renal units, respectively. Eight Memoterm permanent ureteral wall stents were inserted into 7 patients when endoureterotomy failed. Successful outcome was defined by the absence of re-stricture assessed both clinically and radiologically.

RESULTS

The strictures were secondary to ureterolithotomy in 6, ureteroscopy in 3, gynecological procedures in 4, abdominal surgeries in 2, transplantation in 2 and continent urinary diversion in 1. The right and left ureters were unilaterally affected in 5 and 11 patients, respectively (5 of them had a solitary kidney), while the remaining 2 patients had bilateral ureteral strictures. We achieved total ureteral patency of 3 (43%) and 7 (54%) renal units with Acucise and cold-knife incision, respectively. Obstructive uropathy was resolved in 6 renal units (75%) of 8 using ureteral wall stents.

CONCLUSION

Endoureterotomy with cold-knife or Acucise cutting balloon dilatation is effective in the treatment of iatrogenic ureteral strictures, but only in a selected group. Based on our results, the favorable prognostic criteria for endoureterotomy are the length (< or =1.5 cm), the nonischemic nature of the stricture and adequate renal function. As a salvage approach, permanent self-expanding ureteral wall stents with a 75% success rate may provide a satisfactory outcome for decompression of an obstructed system.