Effects of a holmium-166 incorporated covered stent placement in normal canine common bile ducts

PURPOSE: A specially designed self-expandable covered metallic stent incorporated with beta-emitting radioisotope, Holmium-166 (Ho-166), was developed for delivering intraluminal brachytherapy as well as for internal bile drainage in malignant biliary stricture. The purpose of the study was to demonstrate the safety and tissue response of the radioactive metallic stent on the normal canine common bile duct (CBD) prior to the clinical application. MATERIALS AND METHODS: Nitinol self-expandable stents (diameter; 4 mm, length; 20 mm) were covered with polyurethane membrane (50 microm thick) containing 21 to 135 muCi of Ho-166 (mean, 77.9 microCi). To prevent migration of stent, the membrane covered only the middle 1 cm of the stent and the ends of the stent were left uncovered. The stents were placed in the CBD of 20 healthy beagle dogs. For control, non-radioactive covered stents were placed in another three dogs. The dogs were killed 3 to 6 months after stent insertion and histopathologic examination of CBD was performed. RESULTS: There was no stent migration in all cases. Varying degrees of papillary mucosal hyperplasia leading to significant narrowing of the lumen was observed within the lumen of the bare portion and under the mucosal surface of the non-radioactive covered stents. However, fibrosis was noted in Ho-166 coated area, instead of mucosal hyperplasia. Severity of fibrosis was correlated with estimated radiation dose. Despite high dose, there was no perforation of CBD wall. The membrane of Ho-166 coat was disrupted in some cases of 6 months follow-up. CONCLUSIONS: Holmium-166 incorporated covered stents demonstrated fibrosis of CBD wall and inhibition of ingrowth of mucosal hyperplasia without serious complication such as perforation, while control group showed severe mucosal hyperplasia.     

Self-expanding metallic stents: preliminary evaluation in an atherosclerotic model

The performance of the self-expanding stainless steel (Gianturco) stent in atherosclerotic arteries was examined in a rabbit model. Atherosclerosis was induced by supplementing rabbit chow with 6% peanut oil and 2% cholesterol followed by endothelial disruption of the abdominal aorta with a balloon catheter and continuation on the atherogenic diet for the remainder of the study. Eighteen stents, 1 cm in length and 4 or 5 mm in diameter when fully expanded, were placed in atherosclerotic stenotic lesions in six rabbits. Luminal distention was consistently achieved. At 8 weeks follow-up, no luminal narrowing, stent migration, thrombus formation or branch vessel occlusion had occurred. Atherosclerotic neointimal proliferation occurred around the stent wires following placement, but did not cause significant luminal narrowing.     

Stenosis of the vena cava: preliminary assessment of treatment with expandable metallic stents

To test the ability of Gianturco expandable metallic stents to dilate and maintain patency in stenotic venae cavae, stenosis of the inferior vena cava was created in seven mongrel dogs by the percutaneous injection of absolute ethanol into the paravascular retroperitoneal space. Gianturco stents, placed across the stenotic segment, resulted in successful dilatation with improved hemodynamics in four dogs. The stents failed to dilate an occluded vena cava in one dog; in the remaining dogs, stent placement was complicated by early migration and occlusion. Gianturco stents were placed in two patients, one with superior vena cava syndrome and one with retroperitoneal fibrosis that obstructed the inferior vena cava, and resulted in immediate relief of presenting symptoms. These results should be viewed cautiously, but further investigation into the clinical use of the stents is indicated, especially for patients for whom other treatments are difficult.     

Self-expanding metallic stents for small vessels: an experimental evaluation

Thirty-three self-expanding metallic stents were placed in 24 arterial segments of the hind legs and nine arteries of the abdominal viscera in seven dogs. Twelve 5-mm stents, eight 4-mm stents, and 13 3-mm stents were inserted. Follow-up ranged from 4 to 30 weeks. All 4-mm and 5-mm stents were patent at follow-up. Seven (54%) of the 3-mm stents remained patent. Stent wires were completely covered by a proliferation of the intima. No stent migration, occlusion of side branches, or vessel wall perforation was observed. A stent/artery ratio (SAR) was computed using stent and recipient vessel diameters. Good vascular patency was observed when the SAR was less than or equal to 1.2. An SAR greater than 1.2 was associated with immediate spasm, immediate or delayed thrombosis, or excessive intimal proliferation. Selection of correct stent size is a major determinant of patency in small arteries.     

Treatment of experimentally induced atherosclerosis in swine iliac arteries: A comparison of self-expanding and balloon-expanded stents

Atherosclerosis was induced in 20 Hanford miniature swine. Subsequently, one iliac artery lesion in each of 16 pigs was stented with either a self-expanding (8 pigs) or a balloon-expanded (8 pigs) stent. Immediately after stent placement, 4 animals in each group were taken off the atherogenic diet and continued on normal chow for the remainder of the study. Four months after stents were placed, atherosclerosis and the mural changes associated with the stent were more clearly evident in the arteries of the pigs continued on the atherogenic diet. These pigs also exhibited significantly more neointimal proliferation. In addition, the arteries containing the balloon-expanded stents showed more extensive and complex intimal changes when compared with arteries with self-expanding stents. Although both stent designs were equally effective in maintaining vascular patency, the balloon-expanded stent was more traumatic to the vessel wall which resulted in a significantly greater neointimal thickness.     

Intraureteral metallic endoprosthesis in the treatment of ureteral strictures

OBJECTIVE: We report our experience on intraureteral metallic stents placement for the treatment of malignant and benign ureteral strictures. METHODS: Eight patients (six men and two women) with inoperable malignant or benign ureteral strictures, underwent insertion of metallic stents through percutaneous tracts. Six lesions (three malignant, three benign) involved ureterointestinal anastomoses after cystectomy for bladder cancer and ureteroileal urinary diversion or bladder substitution, and two malignant lesions involved the midureter. Self-expandable stents were used in seven cases and a balloon-expandable stent in the remaining one case. One stent was sufficient in seven ureters, and in one ureter, two overlapping stents were placed. RESULTS: Metallic stents were inserted without technical difficulties in all obstructed ureters and patency was achieved in all patients. Ultrasonography revealed resolution of pre-existing hydronephrosis. The duration of follow-up was 6-17 months (mean, 9 months). One ureter was occluded 8 months after stent placement because of ingrowth of tumor and granulation tissue. The other ureters showed no signs of obstruction during follow-up. No major complications directly attributable to the metallic stent occurred. CONCLUSIONS: Our results suggest that insertion of a metallic stent in the ureter is feasible and safe for the treatment of benign or malignant ureteral strictures. However, more work needs to be done to establish the use of these stents for the treatment of ureteral obstruction.     

Influence of a dexamethasone-eluting covered stent on tissue reaction: an experimental study in a canine bronchial model

This study was designed to evaluate the feasibility and efficacy of a dexamethasone (DXM)-eluting, covered, self-expanding metallic stent to reduce tissue reaction following stent placement in a canine bronchial model. We placed a DXM-eluting, polyurethane-covered, self-expanding metallic stent (drug stent, DS) and a polyurethane-covered, self-expanding metallic stent (control stent, CS) alternately in each left main bronchus and left lower lobe bronchus in 12 dogs. The stents were 20 mm in diameter and length when fully expanded. The dose of DXM was approximately 36.7 mg in each DS, but was absent in the CS. The dogs were euthanased 1 week (n=4), 2 weeks (n=4) or 4 weeks (n=4) after stent placement. Histologic findings, such as epithelial erosion/ulcer or granulation tissue thickness, were obtained from the mid-portion of the bronchus, where the stent had been placed, and evaluated between DS and CS. There were no procedure-related complications or malpositioning of any of the bronchial stents. Stent migration was detected in one dog just before euthanasia 1 week following stent placement. Stent patency was maintained until euthanasia in all dogs. Epithelial erosion/ulcer (%) was significantly less in the DS (mean±standard deviation, 46.88±23.75) than in the CS (73.75±14.08) (P=0.026) for all time-points. There was a decrease in epithelial erosion/ulcer as the follow-up period increased in both DS and CS. The granulation tissue thickness (mm) was less in DS (2.63±2.05) than in CS (3.49±2.95), although the difference was not significant (P=0.751) for all time-points. There was a tendency toward an increase in granulation tissue thickness and chronic lymphocytic infiltration as the follow-up period increased in both DS and CS. In conclusion, DXM-eluting, covered, self-expanding metallic stent seems to be effective in reducing tissue reaction secondary to stent placement in a canine bronchial model.     

Treatment of a malignant stricture after esophagojejunostomy by a self-expanding metallic stent

Gianturco self-expanding metallic stents (GSs) were placed across an esophagojejunostomy which had become strictured secondary to recurrent anastomotic gastric cancer. Placement of the GS enabled the patient to take liquid food and swallow saliva, though only for a short period of time. One month after placement, the stented lumen restrictured with a markedly irregular contour. The patient's clinical status deteriorated with eventual occlusion of the stented anastomosis. The patient died of renal insufficiency 80 days after placement of the stent. There are some questions concerning the stability of applying the Gianturco-type bare stent to the digestive tract. In the future, more suitable stents will have to be developed.     

Renal Transplant Ureteral Stenosis: Treatment by Self-Expanding Metallic Stent

We report the use of a metallic stent in a transplant ureteral stenosis. A 28-year-old man with chronic renal failure due to chronic pyelonephritis, who received a living-donor renal transplant, presented with transplant ureteral stenosis. The stenosis was unresponsive to balloon dilation and was treated by antegrade placement of a self-expanding Memotherm stent. The stented ureter stayed patent for 3 years. It may be reasonable to treat post-transplant ureteral stenosis resistant to balloon dilation with self-expanding metallic stents. However, long-term follow-up is required to evaluate the efficacy of this treatment.     

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.     

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.     

Self-expanding and balloon-expandable stents in the treatment of carotid aneurysms: an experimental study in a canine model.

PURPOSETo assess the efficacy of metal stents for the treatment of different forms and sizes of carotid aneurysms.METHODSA total of 14 experimentally constructed aneurysms in dogs were treated with transfemorally placed balloon-expandable tantalum and self-expanding nitinol stents.RESULTSIn 10 cases, stenting produced either immediate complete occlusion of the aneurysm (n = 7) or complete delayed thrombosis after 7 to 10 days (n = 3). In two cases treated with balloon-expandable tantalum endoprostheses, repeated angiography showed a persistent aneurysmal neck with a diameter of 1 mm. No incompletely occluded aneurysms were visible after implantation of nitinol stents. Nine-month angiographic follow-up revealed maximal stenosis of the stented vessel segment of up to 40% after placement of tantalum endoprostheses. However, no more than 15% stenosis followed the deployment of nitinol stents. Histologic examination confirmed these findings. Significantly greater intimal fibrocellular tissue growth surrounded tantalum filaments than nitinol filaments, which were covered with a smooth, thin neointimal layer. In two carotid arteries a subtotal and total occlusion of the parent vessel occurred after the insertion of a tantalum and nitinol stent, respectively. No recanalization of completely occluded aneurysms or delayed migration of a stent was observed.CONCLUSIONSPorous, tubular self-expanding nitinol stents may become the treatment of choice for broad-based and fusiform aneurysms of the internal carotid artery. However, blood flow dynamics of the aneurysms must be studied carefully in order to select an appropriate mesh size for complete occlusion while preserving the parent vessel. Improvements in the introducing system, stent material, and stent shape are required for simple implantation and reduction of intimal hyperplasia.     

Gianturco self-expanding stents: Clinical experience in the vena cava and large veins

Twenty-five patients with stenosis of the vena cava (21) and other large veins (4) have been treated with self-expanding Gianturco metallic stents. Eighteen patients had superior vena cava syndrome. In 17, the stricture was due to malignant superior vena cava compression recurrent after maximum tolerance radiotherapy and/or chemotherapy. In 16 of these patients there was early symptomatic relief. In 1 patient with a benign posttraumatic superior vena cava stricture, the stenosis was not relieved, and occlusion occurred after 1 month. Stenoses associated with dialysis shunts were relieved in 2 other patients. Two malignant and one benign inferior vena cava stenoses were relieved either until death, or in the benign case, for 30 months. One malignant subclavian vein obstruction occluded after 24 h due to stent misplacement and another with extrinsic mediastinal compression remained patent until death, extensive thrombus having been lysed prior to stent placement. The results of this short series suggest that the Gianturco self-expanding stent in the vena cava and large veins is easy and safe to place, and in most cases produces almost immediate palliation of the distressing effects of venous obstruction, often in a preterminal and inoperable patient.     

Metallic stent placement in the pancreatic duct: an experimental study in the normal dog pancreas

PURPOSE: To evaluate radiologic and histologic changes in the pancreatic duct and parenchyma after placement of metallic stents in normal dog pancreatic ducts. MATERIALS AND METHODS: Eight dogs underwent duodenotomy and placement of a balloon-expandable metallic stent 1.5 mm in diameter and 1 cm in length in the main pancreatic duct. Two dogs each were killed at 1 day and 1, 3, and 5 months after stent placement. Pancreatic duct injection images were obtained before and immediately after stent placement and just before and after sacrifice. Macroscopic and microscopic examinations were also performed. RESULTS: Pancreatic duct injection images revealed mild dilation of pancreatic ducts related to the procedure immediately and 1 day after stent placement. Microscopically, denudation of the ductal epithelium and small foci of fat necrosis were observed. At 1 month or later, ductal stricture (n = 4) and occlusion (n = 2) were found at the downstream edge of the initially stent-implanted region associated with dilation of the duct upstream. Epithelial hyperplasia was observed at the sites of ductal stricture and occlusion at 1 and 3 months. Stents remained in the region in which they were initially placed until 1 month. However, stents had moved downstream from their initial positions at 3 and 5 months. One stent had migrated into the duodenum at 5 months. Stone formation was found in the ductal lumen and around the stents at 3 and 5 months. Ducts and parenchyma became fibrotic proportional to the period of stent implantation. CONCLUSION: Metallic stent placement in the pancreatic duct causes ductal and parenchymal damage related to the procedure and reaction to the stent in the normal dog pancreas.     

Iliac artery stenosis and occlusion: preliminary results of treatment with Gianturco expandable metallic stents

Ten patients with atherosclerotic stenosis or occlusion of the iliac artery were treated with Gianturco expandable metallic stents. In the five cases of stenosis, only balloon dilation was performed prior to placement of stents. The five patients with occluded arteries were given intraarterial infusions of urokinase before balloon dilation and stent placement. Clinical symptoms improved in all patients, and no technical failures or complications occurred. Doppler ankle-brachial index studies were performed in nine cases, and in all nine cases the indexes improved after stent placement. During follow-up of 2-18 months (mean, 10.3 months), all arteries remained patent. Follow-up angiograms showed slight intimal thickening and no restenosis. Long-term follow-up and more clinical experience will be necessary to evaluate the efficacy of this stent. However, preliminary results suggest that the Gianturco expandable metallic stent is of value in the treatment of arterial occlusive disease.     

Effect of a metallic balloon-expanded stent on normal rabbit ureter.

Two-millimeter balloon-expanded Gianturco-Roubin coronary artery stents were placed in the 1-mm-diameter distal ureters of five normal rabbits. Retrograde pyelograms obtained immediately after stent placement showed no obstruction or extravasation of contrast material. Follow-up excretory urograms were obtained for each animal between 4 and 17 days, and autopsy was performed between 35 and 42 days. Findings at excretory urography and autopsy demonstrated severe obstruction at the level of the stent in each animal. Histologic examination of the resected ureter was performed. In four animals, the stent had penetrated into the wall of the ureter and a fibrous reaction had obliterated the lumen. In one animal, although the stent was still present within the lumen of the ureter, a fibrous reaction within the wall had destroyed the muscle layers and narrowed the lumen at the distal end of the stent. It is concluded that the 2-mm Gianturco-Roubin stent is unsuitable for placement in the 1-mm rabbit ureter.     

被覆支架成形术在食管癌姑息治疗中的应用

为了对中晚期食管癌进行姑息治疗，作者采用涤纶被覆金属支架置入术对１６例食管癌患者进行了治疗，其中合并食管气管瘘者４例。支架的体部直径为１８ｍｍ或１２ｍｍ，支架两端直径是２２ｍｍ，支架体部和端部的连接处成钝角，以防止支架的移位。全部支架置入术均经口腔在Ｘ线监视下进行。所有病人的支架留置均获成功，未出现技术问题。在有食管气管瘘的４例中，支架置入后症状均得到缓解，所有病人的摄食能力均有不同程度地改善。食     

Venous stenoses in dialysis shunts: treatment with self-expanding metallic stents

A flexible, self-expanding metallic endoprosthesis was employed for the treatment of venous outflow stenoses in four patients with a polytetrafluoroethylene shunt and two patients with a Brescia-Cimino shunt. The stenoses had led to shunt occlusion in five patients and to flow impairment in one. In the occluded shunts, thrombectomy and subsequent balloon angioplasty were performed in four patients, and percutaneous recanalization with angioplasty was performed in one. One shunt with decreasing flow was percutaneously dilated. Since the underlying stenoses recurred in four patients after 24 hours and did not respond sufficiently to angioplasty in two patients, up to four stents were placed in the venous segments. Thrombosis of the stents occurred in two patients after 24 hours and in one after 6 weeks and was successfully recanalized with thrombectomy in two. At 2-6 months follow-up, the stents and the shunts were patent in five patients. In three of these patients, intima hyperplasia, associated with narrowing of the stent lumen in two, was noted within 4 months after stent placement.     

Self-expanding endovascular graft: an experimental study in dogs

An arterial endovascular graft was constructed by wrapping an expandable nylon mesh around a framework of Gianturco self-expanding metallic stents. The devices were passed through a 12-French Teflon catheter and positioned in the normal abdominal aorta of five dogs, two of which also had a device placed in an external iliac artery. At follow-up (1-6 months), all grafts remained patent, even though slight luminal narrowing due to neointimal encasement was noted. Histologically, all grafts were covered by neointimal proliferation at the time of removal. The graft material expanded with the stents, resulting in a tight fit between the graft and the vessel wall. Side branches narrowed but remained open because of the size of the nylon mesh. No migration of the grafts equipped with a barbed lead stent was noted. Expandable nylon mesh can be used as an endovascular graft material when wrapped around a framework of self-expanding stents. The resulting device can be easily delivered via transcatheter techniques, and once placed in a vessel, the nylon acts as a support for neointimal encasement, which forms a new vascular lumen.     

Expandable Metallic Stent Treatment for Malignant Colorectal Strictures

Four patients were treated by placement of an expandable metallic stent (two Gianturco Z-stents, two Ultraflex stents) for malignant colorectal strictures. All four patients were able to defecate after stent placement. Stent migration was recognized in one patient. Two patients suffered from tenesmus after stent placement.