Evaluation of the Effects of Temporary Covered Nitinol Stent Placement in the Prostatic Urethra: Short-Term Study in the Canine Model

Purpose To evaluate the effect of temporary stent placement on the canine prostatic urethra. Methods Retrievable PTFE-covered nitinol stents were placed in the prostatic urethras of 8 beagle dogs under fluoroscopic guidance. Retrograde urethrography was obtained before and after stenting. Retrograde urethrography and endoscopy were performed 1 and 2 months after deployment. The endoscopic degree of hyperplasia was rated on a scale of 0 to 4 (0 = absence, 4 = occlusion). On day 60, stents were removed and urethrography was performed immediately before euthanasia. Pathologic analysis was performed to determine the degree of glandular atrophy, periurethral fibrosis, and urethral dilation. Results Stent deployment was technically successful in 7 animals, and failed in 1 dog due to a narrow urethral lumen. Complete migration was seen in 2 animals at 1 month, and an additional stent was deployed. On day 30, endoscopy showed slight hyperplasia (grade 1) in 3 animals. On day 60, moderate hyperplasia (grade 2) was evidenced in 4 cases. No impairment of urinary flow was seen during follow-up. Retrieval was technically easy to perform, and was successful in all dogs. The major histologic findings were chronic inflammatory cell infiltrates; prostate glandular atrophy, with a mean value of 1.86 (SD 0.90); periurethral fibrosis, with a mean ratio of 29.37 (SD 10.41); and dilatation of the prostatic urethra, with a mean ratio of 6.75 (SD 3.22). Conclusion Temporary prostatic stent placement in dogs is safe and feasible, causing marked enlargement of the prostatic urethral lumen. Retrievable covered stents may therefore be an option for bladder outlet obstruction management in men.     

Tissue hyperplasia: influence of a paclitaxel-eluting covered stent--preliminary study in a canine urethral model

PURPOSE: To evaluate a paclitaxel-eluting covered stent in reduction of tissue hyperplasia after stent placement in a canine urethral model. MATERIALS AND METHODS: Procedures were performed in accordance with the National Institutes of Health guidelines for humane handling of animals; approval of the committee of animal research was obtained. Twenty paclitaxel-eluting polyurethane-covered stents (drug stents) and 20 polyurethane-covered stents (control stents) were placed alternately between the proximal and distal urethra in 20 male dogs. The dose of paclitaxel was approximately 1800 mug in each drug stent but absent in each control stent. Dogs were sacrificed either 4 (n = 10) or 8 (n = 10) weeks after stent placement. The percentage diameter of stenosis was assessed with follow-up retrograde urethrography and histologic findings obtained after sacrifice and compared between drug stents and control stents and between the proximal and the distal urethra. RESULTS: Two drug stents partially migrated during retrograde urethrography immediately after stent placement; they were removed and replaced with a second stent during the same procedure. There was a strong tendency toward a lower percentage diameter of stenosis and numeric mean values of the four histologic findings, which indicates less formation of tissue hyperplasia in the proximal urethra than in the distal urethra. In particular, thickness of the papillary projection denoting the entire thickness of hyperplastic reaction was significantly less in drug stents than in control stents in the proximal urethra in the 8-week group (P = .016, Mann-Whitney U test). CONCLUSION: Local delivery of paclitaxel via covered stents has the potential to reduce tissue hyperplasia secondary to stent placement in a canine urethral model. With stent placement, there are distinct differences of tissue hyperplasia between the proximal and distal urethra.     

Prostatic urethra dilatation with the Gianturco self-expanding metallic stent: a feasibility study in cadaver specimens and dogs.

In an effort to develop a transcatheter technique for dilatation of the prostatic urethra without the use of balloons, the feasibility of using Gianturco self-expanding stents was evaluated. Initially, eight human cadaveric prostatic urethras were stented to evaluate the ability of the stent to dilate the lumen. In all cases, the device attained its unconstrained diameter immediately on placement. Subsequently, stents were placed in the prostatic urethra of 12 dogs and followed up for 1 month (four dogs), 3 months (one dog), and 6 months (seven dogs). Five bare straight-end prostheses, one nylon-covered straight-end device, and six flared-end stents were used. Three of the bare straight-end stents migrated during the follow-up, whereas the nylon-covered and flared-end stents did not. Stent diameters greater than 1.3 times the urethral diameter caused moderate to marked edema and inflammation. After 6 months, white deposits were found on the solder points, presumably from electrolysis. Our experience suggests that placement of Gianturco self-expanding stents may be a useful method of dilating and maintaining the luminal diameter of the prostatic urethra, although care must be taken to select the proper stent size.     

Self-expanding stents in transjugular intrahepatic portosystemic shunt: experience with nitinol Strecker stents

The aim of our study was to evaluate the performance and efficacy of a new self-expanding stent (nitinol Strecker stent) in the transjugular intrahepatic portosystemic shunt (TIPS) procedure. We have successfully placed 64 nitinol Strecker stents in 48 patients. The average portosystemic gradient decreased from 22 to 11 mm Hg. Balloon dilatation was necessary in 12 of 35 angiographically controlled cases at 5 days (34%), because of incomplete stent expansion, small thrombi within the stent or obstruction. At 1–6 months stent malfunctions occurred in 8 of 23 patients who underwent control angiography (34%) and at 6–24 months in 6 of 7 patients (85%). Rebleeding occurred in 2 of 39 patients (follow-up > 1 month) (5%) and temporary crises of de novo encephalopathy were observed in 11 of 48 patients (23%). Refractory ascites completely resolved in 4 of 6 patients (66%) and improved in the remaining 2 cases. Compared with other self-expanding stents, nitinol Strecker stents seem to be equally effective in TIPS; no increase in complication rate was observed, either clinical or stent-related. Correspondence to: P. Rossi     

Renal cyst pseudoenhancement: evaluation with an anthropomorphic body CT phantom

PURPOSE: To evaluate the feasibility of using a retrievable urethral stent and to evaluate whether granulation tissue resolves after stent removal in a canine urethra. MATERIALS AND METHODS: Polyurethane-covered retrievable 0.10-mm-thick (n = 11) or 0.15-mm-thick (n = 10) nitinol wire stents were placed in the urethras of 20 dogs. In one dog, a second stent was placed in the urethra because of complete migration of the first stent into the urinary bladder. The stents were removed with retrieval hook wires 4 weeks (n = 10) and 8 weeks (n = 10) after placement. Fourteen dogs were sacrificed just after stent removal, and the other six dogs were sacrificed 2 weeks after stent removal. Information concerning procedure success, stent migration, and tissue response was obtained. RESULTS: Stent placement was technically successful in all dogs. Follow-up urethrograms showed partial (n = 4) or complete (n = 1) stent migration. Stent removal failed in two dogs due to partial or complete migration. Granulation tissue was observed at both ends of the stent in 17 dogs. Urethrograms and urethral specimens obtained 2 weeks after stent removal showed diminished granulation tissue and decreased thickness of the papillary projections of the epithelium compared with results obtained immediately after stent removal. CONCLUSION: Although some design modifications are necessary to reduce current complications, the polyurethane-covered retrievable nitinol stent seems feasible for use in the urethra. Stent-induced granulation tissue formation improved after stent removal.     

Experimental study of the intraurethral placement of expandable metallic stents

Various types of Gianturco expandable metallic stents were implanted into the urethra of four dogs in order to evaluate the suitable expandability of the stents in urethra and also to determine the effect of the stents on the urethral wall. The stent of 1.5 cm in length and constructed of 0.010 inch round stainless steel wire with twelve zigzag bends showed the suitable expandability on the canine urethra compared to the other stents. The urethra remained patent and the inflammatory changes on the urethral wall were moderately noted. No hematuria or calcifications around the stents were noted in any dogs. The experimental data showed a potential clinical application.     

Is a flared stent effective for decreasing stent migration in canine prostatic urethra?

Background: Prostatic urethral stents are effective in relieving obstructions caused by benign prostatic hyperplasia (BPH). However, migration of these stents occurs frequently.

Purpose: To evaluate the efficacy of a flared stent for decreasing the migration rate in comparison with a straight stent in a canine prostatic urethral model.

Material and Methods: The flared stent (15 mm in diameter and 20 mm in length) was flared up to 19 mm at both ends to prevent migration. A straight stent with the same size was straight without flaring. Both stents were made of a nitinol wire filament and covered with an expanded polytetrafluoroethylene (ePTFE) membrane. The flared stent was inserted in the prostatic urethra of 10 dogs (group 1) and the straight stent in the prostatic urethra of 12 dogs (group 2). Follow-up retrograde urethrography (RUG) was performed 1, 4, and 8 weeks after stent placement. Fisher's exact test was used to compare the migration rate between the two groups. When stent migration occurred during the follow-up period, the same type of stent was inserted again.

Results: Three of 10 (30.0%) flared stents migrated into the urinary bladder between 1 week and 4 weeks after placement. Seven of 12 (58.3%) straight stents migrated into the urinary bladder 1 (n = 3), 4 (n = 1), and 8 (n = 3) weeks following placement. The flared stent group showed lower migration rate than the straight stent group, but the migration rate did not reach statistical significance (P = 0.231). After the second stent placement, one of three (33.3%) flared stents migrated again after 4 weeks and two of seven straight stents (28.6%) after 1 week.

Conclusion: Although the migration rate was not statistically significant, the flaring of the stent seemed to reduce the migration rate in comparison with straight stents in a canine prostatic urethral model. However, the migration rate of the flared stent was still high, and further developments are required to decrease migration rate.     

Treatment of malignant dysphagia with nitinol stents

Self-expanding nitinol stents were used in 22 patients for palliative treatment of malignant esophagogastric strictures. All patients but 5 were men (age range 47–75 years). The strictures were caused by squamous cell carcinoma (n = 12), adenocarcinoma (n = 8), and recurrent anastomotic carcinoma (n = 2). No technical failure or procedural complications occurred. After the procedure, the severity of dysphagia decreased at least one grade in all patients. Tumor ingrowth into the stent was seen in 7 patients of 22 (32%). Four of these patients were treated with additional stents, and in 3 patients, due to refusal, only balloon dilations were performed, which caused temporary relief. Tumor ingrowth into the stent was noted from 10 days to 7 months (mean 3 months). This seems to be a disadvantage of nitinol stents. At the end of the study 10 patients had died dead with a mean survival of 3 months (range 1 week to 6 months) and 12 patients were still alive with a mean follow-up of 4 months (range 1–8 months). It is concluded that nitinol stents provide satisfactory palliation in patients with malignant dysphagia with neglectable procedural morbidity and mortality rates.     

Hemodynamics and wall mechanics after stent placement in swine iliac arteries: comparative results from six stent designs.

PURPOSE: To compare the hemodynamics and wall mechanics of swine iliac arteries after placement of six types of stent. MATERIALS AND METHODS: Stents were placed in the iliac artery of 18 pigs (three pigs each underwent placement with one of six types of stent); 16 untreated pigs served as control animals. Iliac arterial hemodynamics and wall mechanics were measured 4 days after placement. RESULTS: Four stents (Palmaz-Schatz, Cordis, Warren, NJ; and Strecker, Cragg, and Symphony, Boston Scientific/Vascular, Natick, Mass) caused decreased pulsatile flow rate in the treated and contralateral iliac arteries; one (Memotherm; Bard, Covington, Ga) caused increased flow pulsatility; and one (Wallstent; Schneider, Plymouth, Minn) had no effect. No compliance mismatching was noted for the Cragg, Symphony, and Memotherm stents, whereas a decrease in compliance was noted for the Palmaz-Schatz, Strecker, and Wallstent designs. The Palmaz-Schatz and Strecker stents caused increased arterial wall rigidity, the Symphony and Wallstent designs had no effect, and the Memotherm and Cragg stents caused decreased wall rigidity. Stents made of stiff metal yielded different early results than did stents made of the less rigid nitinol. CONCLUSION: Soon after implantation, the six stent designs elicited varying changes in blood flow, arterial compliance, and arterial wall mechanics. Contralateral arterial flow also was affected.     

Metallic stents for treatment of benign biliary obstruction: a long-term study comparing different stents

PURPOSE: To investigate the role of metallic stents in the treatment of benign biliary strictures and analyze the differences in primary patency associated with the various types of stents deployed. MATERIALS AND METHODS: Between 1990 and 1997, 21 patients with benign obstructive jaundice were treated with transhepatic placement of metallic stents (11 Wallstents in 10 patients, nine Palmaz stents in seven patients, and four tantalum Strecker stents in four patients). Nineteen patients presented with strictures not responding to balloon angioplasty (postsurgical, n = 13; cholangitis, n = 5; unknown, n = 1). Estimates for cumulative patency, patency rate in the different stent groups, and survival were calculated with use of life-table analysis; the log-rank test was used to compare the different stent groups. The prognostic relevance of the selected variables-stent type, stent length, etiology, and location-were modeled with respect to patency according to Weibull distribution. RESULTS: The median follow-up time was 80.5 months (range, 2-116 months). The median survival time was 91 months. One patient was lost to follow-up after 3 months. Repeat intervention for recurrent obstructive jaundice was necessary in 11 patients (55%), and the median patency rate was 26 months (range, 2-96 months). The Palmaz stent was the most effective in achieving long-term patency, with a median patency duration of 36 months (range, 22-96 months), versus 9 months (range, 3-67 months) for the Wallstent and 6 months (range, 2-15 months) for the tantalum Strecker stent. The cumulative patency rate with the Palmaz stent was significantly higher than for the tantalum Strecker stent (log-rank test, P = .017) and nonsignificantly higher compared with the Wallstent (log-rank test, P = .07). Multivariate analysis showed that the type of stent (Wald test, P = .003) and stent length (Wald test, P < .0001) influenced the patency rate. CONCLUSIONS: These results suggest that the type of stent and the stent length have a significant influence on the patency rate. In this series, the Palmaz stent was most effective in achieving long-term patency in benign biliary strictures.     

Iliac artery stenting--clinical experience with the Palmaz stent, Wallstent, and Strecker stent.

A total of 82 iliac artery lesions (62 stenoses and 20 occlusions) were treated with 3 different types of endovascular metallic stents (12 lesions with the Palmaz stent, 36 with the Wallstent, and 34 with the Strecker stent). The complication rate was 12%. Occlusion of 2 Wallstents occurred 4 and 12 weeks after stent placement, respectively. Both stents were recanalized by local fibrinolysis. One Strecker stent occluded after 8 months. The observation period was 3 to 26 months (mean 9.7 months). The patency rate with secondary intervention (fibrinolysis) was 100% after 3 and 6 months, and 98% after 9 months. All 3 stent designs turned out to be effective in the treatment of complicated iliac artery occlusive disease.     

尿道内支架置入术初步实验研究

目的：主要了解尿道粘膜对内支架置入后的反应。材料与方法：雄性犬５条。球囊扩张式钽丝支架（Ｓｔｒｅｃｋｅｒｓｔｅｎｔ），内支架扩张后内径６ｍｍ。先行逆行尿道造影后，支架置入前列腺部位尿道内，术后３天、２周和１个月造影复查，取病理检查。结果：造影复查显示尿道通畅，有１例内支架移位。病理巨检见支架与尿道结合紧密，支架网眼内粘膜增生，镜检示粘膜上皮细胞增生，结缔组织内有炎性细胞浸润及小血管增生，电镜下钽丝表面光滑。结论：粘膜上皮对该内支架无明显炎性反应，适用于前列腺成形术。     

Palliative treatment of neoplastic strictures by self-expanding nitinol Strecker stent

The purpose of this study was to evaluate technical and clinical results of self-expanding esophageal stent implanted in patients with malignant esophageal strictures and clinically significant dysphagia. From June 1992 to September 1994, 27 patients with inoperable tumors of the esophagus or gastric cardiac were treated by placement of 37 self-expanding nitinol stents. Water-soluble contrast and endoscopy studies were performed after the procedure and during the follow-up period. Successful stenting of the stricture was achieved in 27 patients. The mean dysphagia grade dropped from 2.3 to 1 (SD ± 0.54) immediately after the procedure. After the insertion of the stent, 16 patients died in a period of time ranging from 0 to 13 months (mean 5.6 months), whereas at the end of the study 11 patients were alive 4–15 months after the procedure (mean 8.3 months). No major complications were observed. The results of this study are encouraging because esophageal stent placement was technically easy and clinically effective. Correspondence to: F. Maspes     

Polydioxanone Biodegradable Stent Placement in a Canine Urethral Model: Analysis of Inflammatory Reaction and Biodegradation

PurposeTo investigate the inflammatory reaction and perform quantitative analysis of biodegradation after placement of a polydioxanone (PDO) biodegradable stent in a canine urethral model.Materials and MethodsPDO biodegradable stents were placed in the proximal and distal urethra of nine male mongrel dogs. The dogs were euthanized 4 weeks (group A; n = 3), 8 weeks (group B; n = 3), or 12 weeks (group C; n = 3) after stent placement. The luminal diameter of the stent-implanted urethra was assessed by follow-up retrograde urethrography, and histologic findings were obtained after the dogs were killed. Stents were removed after euthanasia, and their surface morphology and molecular weight were evaluated. Hematologic examination was performed to evaluate inflammatory reaction.ResultsStent placement was technically successful in all dogs. The average luminal diameter gradually decreased. The average number of epithelial layers (2.93 vs 4.42; P < .001), the average thickness of papillary projection (0.80 mm vs 1.28 mm; P < .001), and the average thickness of submucosal fibrosis (0.34 mm vs 0.49 mm ; P < .001) were significantly increased in group B versus group A. There were no significant differences between group B and group C. The average inflammatory cell infiltration did not differ significantly in the three groups. Molecular weight losses were 54% in group A and 84% in group B. In group C, PDO stents were completely decomposed.ConclusionsAn experimental study in a canine urethral model has demonstrated acceptable inflammatory reaction with gradually increasing granulation tissue but no luminal obstruction within 12 weeks.     

Recurrent traumatic urethral strictures near the external sphincter: treatment with a covered,retrievable, expandable nitinol stent--initial results

PURPOSE: To investigate the clinical effectiveness of a covered, retrievable, expandable nitinol stent in treating traumatic urethral strictures near the external sphincter. MATERIALS AND METHODS: The stent was 10 mm in diameter when fully expanded and 40-50 mm long. To make it removable, two nylon drawstrings were attached to its lower inner margin. Twelve consecutive men (19-67 years; mean age, 47 years) with traumatic urethral strictures near the external sphincter that were refractory to endoscopic urethrotomy were treated. With fluoroscopic guidance, a stent was placed to completely bridge the external sphincter. The stent was electively removed with a retrieval hook wire 2 months after placement. Stent placement and removal were successful in all patients, with no procedural complications. RESULTS: Mean maximum urine flow rate was 5 mL/sec (range, 3-7 mL/sec) before stent placement and 27 mL/sec (range, 16-40 mL/sec) at 1 week after placement. During the mean follow-up of 20 months (range, 2-37 months) after the first stent removal, strictures recurred in eight of 12 patients. For the eight patients with recurrence, a second stent was placed and 4 months later was removed from seven of the eight patients. During the mean follow-up of 18 months (range, 4-32 months) after the second stent removal, strictures recurred in two patients, in whom a third stent was placed and then removed 4 months later, with good results. Four (33%) of 12 patients, five (62%) of eight patients, and two (100%) of two patients were successfully treated with placement of the first stent, the second stent, and the third stent, respectively. In the remaining patient, the second stent remains in place. CONCLUSION: Placement of a covered, retrievable, expandable nitinol stent seems to be effective in treating urethral strictures near the external sphincter and warrants further investigation.     

Stricture disease: radiology of urethral stents

Self-expanding metal stents are emerging as an effective alternative treatment in the management of urethral obstruction. The radiologic studies of 33 men with anterior urethral strictures (subprostatic, n = 11; bulbar, n = 22) that had recurred despite repeated optical urethrotomy and dilation were reported. In all patients, the stricture was successfully treated with stent insertion. Urethrography performed 1 month later in 19 patients showed an irregular intrastent lumen of varying degrees due to a hyperplastic urothelial reaction confirmed at endoscopy the same day. Available follow-up urethrograms in seven patients at 3 months showed that the hyperplasia was settling, and by 6 months, the intrastent lumen was smooth and of good caliber. Urethrography revealed postoperative structures in 14 patients. Strictures seen at 1 month (n = 6) were due to initial stent misplacement and were treated with the insertion of a second stent. Strictures seen 3 months after insertion (n = 4) occurred within the stent lumen and were considered to be significant at endoscopy in only one patient. Strictures that developed 6-12 months after stent insertion (n = 4) were not within the stent and were considered to represent genuine new strictures.     

Metallic stent placement for iliac artery occlusive disease

Since 1991, we have performed stent placement for 35 iliac artery lesions in 31 patients. The etiologic diseases were atherosclerotic in 34 patients and traumatic dissection in one. The indications of placement were total occlusion in 3, late restenosis after angioplasty in 5, dissection in 5, and residual stenosis due to inadequate angioplasty in 21. We also performed direct stent placement for one traumatic dissection. The stents used were Wallstents in 10, Palmaz stents in 14, Strecker stents in 9, and Memotherm stents in 2 lesions. Follow-up was performed clinically or angiographically with measurement of the ankle/arm pressure index. Stent placement was successful in all cases, and relief or improvement of symptoms was achieved. The follow-up period ranged from 6-85 months (mean, 37.3 months). Late stent stenosis or occlusion occurred in 6 cases, among which 4 occluded lesions were successfully recanalized by thrombolytic therapy with angioplasty or second stent placement. In total, the primary patency rates were 88% and 77% at two and four years, respectively, while the secondary patency rates were 94% and 94%. In conclusion, metallic stent placement may offer extended application of intravascular treatment for iliac artery occlusive disease, and good long-term patency rates can be expected.     

Results of temporary placement of covered retrievable expandable nitinol stents for tuberculous bronchial strictures

Covered retrievable expandable nitinol stents were successfully placed in nine patients with tuberculous bronchial strictures refractory to balloon dilation. Complications included stent migration (n = 1) and tissue hyperplasia at the proximal portion of the stent (n = 2). During the follow-up period (5-52 months), stricture recurred in three of five patients (60%) after temporary stent placement for 2 months, whereas stricture did not recur in the other four patients after temporary stent placement for 6 months. Temporary placement of covered retrievable stents appears to be an effective method for the treatment of patients with tuberculous bronchial strictures refractory to balloon dilation.     

Temporary metallic stent placement in the treatment of refractory benign esophageal strictures: results and factors associated with outcome in 55 patients

The purpose of this study was to evaluate the effectiveness of temporary metallic stenting in 55 patients with treatment-resistant benign esophageal strictures and to identify factors associated with clinical outcomes. Under fluoroscopic guidance, covered retrievable stents were placed in 55 patients with benign esophageal strictures and were removed with retrieval hook 1 week to 6 months after placement. Stent placement was successful in all patients, and the mean dysphagia score was reduced from 2.8 to 1.3 (p < 0.001). The most common complications were tissue hyperproliferation (31%), severe pain (24%), and stent migration (25%). During follow-up (mean: 38 months), recurrence of the stricture necessitating balloon dilation was seen in 38 (69%) of 55 patients. Maintained patency rates after temporary stenting at 1, 3, and 6 months and 1, 2, and 4 years were 58%, 43%, 38%, 33%, 26%, and 21%, respectively. In multivariate analysis, length (p = 0.003) of the stricture was the only significant factor associated with maintained patency after temporary stenting. In conclusion, temporary metallic stenting for refractory benign esophageal strictures may be effective during the period of stent placement, but is disadvantaged by the high recurrence rates after stent removal, particularly in patients with a long length of stricture (>7 cm).     

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 polyurethane 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.