A New Technique for Reconstruction of the Common Bile Duct by an Autologous Vein Graft and a Biodegradable Endoluminal Stent

The incidence of severe bile duct injuries has significantly increased since the introduction of laparoscopic cholecystectomy. The ideal reconstruction procedure for traumatic defects of the bile duct should be technically simple and should preserve both the physiological passage of bile and the sphincter of Oddi. In this article we describe a new technique for bile duct reconstruction in a pig model by means of an autologous vein graft that is splinted by a endoluminal biodegradable polylactate acid stent. In 12 pigs the external jugular vein was removed and used as an autologous vein graft. After performing a median laparotomy a 2-cm segment was resected from the bile duct. The common bile duct was reconstructed by a venous interponate that had been endoluminally stented by a biodegradable polylactate acid stent. For the examination of stent degradation, 2 pigs were sacrificed at 3, 4, and 5 months (stent degradation group) and the remaining 6 pigs at 6 months (survival group). All the pigs in the survival group survived for 6 months before being sacrificed. After 4 months the stent material had been completely broken down and the vein graft had been relined with bile duct epithelium. Thus, this new technique for bile duct reconstruction using an autologous vein graft with an endoluminal stent is simple to perform and reliable, and constitutes an interesting alternative to bilodigestive anastomosis due to the preservation of the papilla of Vateri.     

Morphological Changes during Creation of a Neo-Bile Duct Using a Vein and a Biodegradable Endoluminal Stent

ABSTRACT?

Major bile duct lesions are usually treated by a hepaticojejunostomy which is often complicated by cholangitis and liver fibrosis. The aim of this study was to investigate the morphologic features of a neo-bile duct created from a vein and a biodegradable endoluminal stent. The neo-bile duct was created using a segment of the external jugular vein which was endoluminally stented by a biodegradable poly-lactate-acid stent. In 18 pigs, the common bile duct was resected and replaced by the vein with (n = 12) or without endoluminal stent (n = 6). Six animals served as controls. Survival, liver function and morphological changes of the neo-bile duct and the liver were observed for six months. After six months, the neo-bile duct morphologically resembled the native bile duct showing Ck7-positive columnar epithelium and newly formed capillaries in the bile duct wall. The biodegradable stent disappeared after four months. All animals survived and showed normal liver function and no cholestasis. In contrast, after sole vein reconstruction of the bile duct, four animals died due to biliary peritonitis and cholangitis. Creation of a neo-bile duct which morphologically resembles the native bile duct is feasible by using a body's own vein and a biodegradable endoluminal stent.     

Reconstruction of bile duct lesions by an autologous vein graft and a bio-degradable endoluminal stent in an animal model: technique and clinical impact

INTRODUCTION: In this study a new treatment of bile duct lesions was investigated. A segment of the bile duct was replaced by an autologous venous interponate which had been endoluminally stented with a braided bio-degradable stent. METHODS: A total of 18 pigs (20-28 kg) was divided into three equal groups (I-III). In each group a 2 cm segment of the jugular vein was harvested. The animals in Group I (vein group, n = 6) underwent resection of a 2 cm long segment of the common bile duct which was replaced solely by the venous interponate, in Group II (stent group, n = 6) the venous interponate had been endoluminally stented by a braided bio-degradable stent. Group III (control group, n = 6) underwent only a circular mobilization of the common bile duct. Postoperatively survival rate, general condition as well as the weight were observed and checked for 6 months. During surgery and finally after sacrifice after 6 months blood and tissue samples were taken and semiquantitatively scored concerning grade of inflammation and fibrosis. RESULTS: In the stent and control group all animals survived in good condition. 3 pigs of the vein group died within 3 weeks showing signs of biliary peritonitis, another one died due to a high grade stenosis of the common bile duct with secondary biliary cirrhosis after 4 months. In the stent group all animals survived until sacrifice after 6 months. On examination the venous interponate was laminated with bile duct epithelium showing the diameter of the implanted stent. CONCLUSION: The reconstruction of bile duct lesions by a venous interponate in combination with a bio-degradable stent is easy to perform and represents a clinically interesting alternative to the biliodigestive anastomosis because of the preservation of the sphincter oddi. After 6 months the stent is completely absorbed and the venous interponate is laminated with bile duct epithelium.     

Reconstruction of a Common Bile Duct Injury by Venous Bypass

Hepaticojejunostomy is the standard technique for the reconstruction of severe iatrogenic lesions of the common bile duct (CBD), although the technique itself is major surgery with a complication rate up to 30%. We report a case of a male patient with a iatrogenic complete transsection of the CBD. Due to multiple previous operations and the present inflammation a standard reconstruction technique was not possible to perform. A neo-bile duct was created using a segment of the Great Saphenous Vein (GSV) synchronously with an external biliary drainage by PTCA and biliary stenting (after 4 weeks). The stent was removed 8 months later. Cholangiography showed normal bile flow without occlusion. Blood tests normalised. We believe that using an autologous vein graft in combination with a removable or biodegradable stent is the right track for the reconstruction of the CBD in the future.     

Bile duct replacement using an autologous femoral vein graft: an experimental study. Preliminary results

The repair of common bile duct injuries is a complex procedure with a significant rate of postoperative morbidity and mortality. The aim of this study was to demonstrate the usefulness of the autologous vein graft in replacement of the bile duct. Twelve male Sprague-Dawley rats weighing 350 +- 550 g were used in the study and were divided at random into two groups: the control group (60) and the experimental group in which a 3-mm segment of the bile duct was resected and the biliary tract was replaced by a segment of vein aided by stent (G1). Both groups were subdivided into pairs of rats to study at 30, 60, and 120 days. All of the animals underwent radioisotope cholangiography, a repeat laparotomy, and blood tests for further pathologic study. The clinical evaluation and biochemical nuclear medicine and pathologic studies showed no evidence of cholestasis. The histologic study of the graft showed replacement of the endothelium by biliary-appearing epithelium. The use of an autologous vein graft with a supporting stent proves to be a feasible and alternative procedure for bile duct reconstruction. Further experimental studies should be carried out to validate these findings so they can be implemented in clinical cases.     

Biliary tract reconstruction using an autologous vein graft in rats

Numerous biologic and synthetic materials have been used with limited success as an interposed graft to repair segmental common bile duct (CBD) defects. The authors report here that an autologous vein graft can be successfully used to correct a CBD deficit contingent on accurate microsurgical technique immediate stenting and rapid graft vascularization. Thirty Sprague-Dawley rats underwent laparotomy and the experimental group (n=25) had a 3-mm segment of the CBD excised. The CBD defect was repaired using an interposed femoral vein graft aided by a plastic stent. The control group (n=5) had the CBD cut and repaired by means of primary anastomosis. The experimental group was subdivided into three sub-groups each examined at three different postoperative intervals: 1, 4 and 12 weeks. The results showed that inflammation was apparent in the venous wall following the first postoperative week. A progressive loss of the vascular endothelium and replacement with the columnar epithelium typical of the CBD was seen in the vein graft. Nineteen of the 25 experimental rats (76 percent) of the animals survived without complication from the surgery and there were no abnormalities in the liver biochemical tests of these animals. Any biliary tract obstruction that developed was attributed to dislocation of the stent leading to collapse of the vein graft (experimental group), or constriction of the anastomosis (control group). This study demonstrates that biliary tract reconstruction using an autologous vein graft can be successfully performed in a rat model of CBD repair. The application of this method to the clinical setting is also discussed.     

Reconstruction of ureteral defects with microvascular vein grafts in a rat model

This study was undertaken to test the performance of an autologous vein graft as a ureteral replacement in the rat model. Twenty-six rats were divided into three groups. In Group 1 (n = 10), the animals had a 3-mm segment of the ipsilateral ureter excised and the ureteral defect repaired, using a superficial epigastric vein graft. In Group 2 (n = 10), the same ureteral defect was created and again repaired, using a superficial epigastric vein graft, with the addition of a Silastic stent. The control, Group 3 (n = 6), had the ureter transected and repaired solely by means of primary anastomosis. Animals from each group underwent urography and were sacrificed for histology at three different postoperative intervals: 1, 4, and 12 weeks. Postoperative urography results showed normal renal function in the animals with ureteral reconstruction using vein grafting aided by a stent, as well as in those with primary ureteral anastomosis. No renal function return was seen in the animals with ureteral reconstruction by vein grafting alone, without stent support. Histologically, a progressive loss of the vascular endothelium, and replacement with the urothelium typical of the ureter, was seen in the stented vein grafts. Severe ureteral obstruction at the proximal site of the graft and hydronephrosis were seen in the vein-graft group without stenting. This study demonstrates that autologous vein grafts can be used successfully to correct a ureteral deficit, contingent on accurate microsurgical technique and immediate stenting.     

带蒂脐静脉瓣修复Mirizzi综合征胆管缺损35例体会

目的 总结带蒂脐静脉瓣修复Mirizzi综合征胆管缺损的经验。方法 回顾性分析35例采用带蒂脐静脉瓣修复Mirizzi综合征（Ⅱ型19例、Ⅲ型15例,Ⅳ型1例）的临床资料。结果全组无死亡病例,术后发生胆漏5例,经1～3周引流后痊愈。全部病例拔管后均获6个月的随访,有27例随访达3年,未见明显胆道并发症发生。结论利用带蒂脐静脉瓣修复Mirizzi综合征胆管缺损方法简单、效果较好。     

Portal Vein Interposition Using Homologous Iliac Vein Graft during Extensive Resection for Hilar Bile Duct Cancer

Although autologous vein grafts have been used for portal vein (PV) reconstruction after long-segment portal vein resection during surgery for hilar bile duct cancer, their procurement prolongs operation time and increases morbidity. Less is known regarding the use of homologous vein grafts. The feasibility of homografts for PV reconstruction was preliminarily evaluated in two patients who underwent curative resection for hilar cholangiocarcinoma. Both patients underwent left lobectomy, caudate lobectomy, bile duct resection, and segmental PV resection and interposition vein graft reconstruction. The iliac vein homografts were obtained from deceased organ donors and stored for 1–2 days in cold preservation solution without freezing. Neither immunosuppression nor anticoagulation was attempted. One patient has shown good PV patency for 27 months. The second patient, who had received adjuvant chemoradiotherapy, showed an asymptomatic waisting at the proximal PV anastomosis site after 4 months, which was relieved by percutaneous balloon dilatation, and has been doing well for 12 months. In conclusion, our preliminary experience with these two patients suggests that cold-stored iliac vein homografts can be considered as PV substitutes after long PV segment resection during extensive hepatobiliary surgery.     

Secondary aortoesophageal fistula after endoluminal exclusion because of thoracic aortic transection

Secondary aortoesophageal fistula (AEF) is a rare but catastrophic complication that occurs after thoracic aortic reconstruction. Recently endoluminal stent grafts have been used in selected patients with a thoracic aortic aneurysm, dissection, or traumatic aortic transection. A 24-year-old woman had massive upper gastrointestinal tract bleeding 15 months after endoluminal stent graft placement because of traumatic descending thoracic aortic transection. Evaluation demonstrated an AEF from the mid-esophagus to the endoluminal stent graft. The endoluminal graft was explanted, with primary repair of the thoracic aortic defect and simultaneous primary repair of the esophageal injury. The patient is well 15 months after open repair of the AEF.     

Using the Cystic Duct for Biliary Reconstruction in Dual-Graft Living Donor Liver Transplantation: A Case Report

In Taiwan, living donor liver transplant (LDLT) has accounted for the majority of liver transplantation due to organ shortage. Dual-graft LDLT is a feasible way to resolve the insufficient graft size and remnant liver in donors. We presented a heavy-weight patient underwent dual-graft LDLT, and cystic duct was used to resolve the inadequate bile duct length and limited appropriate position in dual-graft LDLT. We harvested a right lobe graft (segment 5, 6, 7, and 8 without middle hepatic vein) and a left lobe graft (segment 1, 2, 3, and 4 without middle hepatic vein) stepwise, and placed the grafts orthotopically. For proper tension and length of biliary reconstruction, we anastomosed the right intrahepatic duct of the right lobe graft to cystic duct of the recipient. Before the biliary reconstruction, the metal probe was inserted in the lumen of cystic duct in recipient to ensure the patency and destroy the Heister valve of cystic duct, then the internal biliary stent (5 Fr pediatric feeding tube) was placed in the donor's right intrahepatic duct to recipient's cystic duct and common bile duct, which allows the endoscopic removal of the internal stent. The patient has survived more than 16 months with normal liver function.     

Long-term reduction of medial and intimal thickening in porcine saphenous vein grafts with a polyglactin biodegradable external sheath

OBJECTIVES: The development of neointimal hyperplasia with subsequent atherosclerotic deposition has been proposed to cause most late vein graft failures. Our unit has previously demonstrated that placement of a macroporous, loose-fitting polyester external stent prevents neointimal thickening in porcine vein grafts, and has been proposed as a therapeutic strategy to prevent late vein graft failure. To reduce any potential long-term complications of the permanent polyester stent, a study was undertaken to investigate the effect of a biodegradable external stent on porcine vein graft thickening at 1 month and to identify its longer term effects at 6 months. METHODS: Bilateral saphenous vein to common carotid artery interposition grafting was performed in Large White pigs (25-32 kg; n = 6 per time course group) according to UK Home Office guidelines. A commercially constructed loose-fitting 8-mm-diameter polyglactin stent was placed externally around the vein graft on one side, and the contralateral side remained unstented to serve as control. The external stent was designed to biodegrade and hence disappear within 90 days. Grafts were left in situ for 1 month in 1 group of animals, and for up to 6 months in the other group, before explantation. Graft morphometric features were assessed with computer-aided planimetry. RESULTS: At 1 month the vein grafts fitted with the polyglactin stent demonstrated a statistically significant decrease in neointimal thickening (0.038 mm; interquartile range [IQR], 0.035-0.039 mm) compared with the unstented control grafts (0.13 mm; IQR; 0.11-0.19; P = .0012), and also in medial thickening (0.09 mm; IQR, 0.086-0.093) compared with unsheathed control grafts (0.302 mm; IQR, 0.272-0.414; P = .0012). The 6-month polyglactin stented grafts also demonstrated a statistically significant reduction in neointimal thickening (0.049 mm; IQR, 0.047-0.07; P = .0012) compared with control grafts (0.178 mm; IQR, 0.164-0.19), and also in medial thickening (0.105 mm; IQR, 0.095-0.143) compared with unstented grafts (0.421 mm; IQR, 0.35-0.44; P = .0012, Mann-Whitney U test). CONCLUSION: The loose-fitting biodegradable polyglactin external stent reduces porcine vein graft thickening at 1 month, which persists in the long term, even after degradation of the stent itself. This effective removal of the stent may therefore reduce the long-term risks for infection and mechanical complications associated with implanted prosthetic material while still eliciting the primary objective of preventing graft thickening over the long term. Biodegradable external stents therefore have potential advantages over permanent stent material in clinical application. CLINICAL RELEVANCE: Arteriovenous bypass graft failure has a huge economic effect on health care resources, and a devastating effect o the patient. The attenuation of vein wall thickening, with subsequent luminal narrowing and occlusion, is a major goal in improving the longevity of the venous graft, to reduce secondary percutaneous and surgical interventions. The biodegradable external stent demonstrated in this study has possible clinical applications in bypass procedures with autogenous venous tissue, and represents a novel approach to ameliorating the problem of intimal hyperplasia that plagues these grafts.     

Left trisegmentectomy with reconstruction of segment 6 hepatic venous outflow using cryopreserved vein graft

Liver resections that require hepatic vein reconstruction rarely occur. Options regarding venous reconstruction include primary end-to-end reconstruction, reimplantation into the vena cava, or the use of a variety of autologous or synthetic grafts. Cryopreserved vein grafts have recently become available for use. We describe a left trisegmentectomy with bile duct resection/reconstruction during which the segment 6 hepatic vein was reconstructed into the inferior vena cava using a cryopreserved vein graft.     

Biliary-Venous Fistula Complicating Transjugular Intrahepatic Portosystemic Shunt Presenting With Recurrent Bacteremia, Jaundice, Anemia and Fever

A 50-year-old White man with noncirrhotic portal hypertension presented with bleeding from gastric varices. Bleeding was initially managed with band ligation and subsequent transjugular intrahepatic portosystemic shunt (TIPS). Over the next few months, the patient had recurrent episodes of anemia, jaundice, fever and polymicrobial bacteremia. Computed tomography (CT) of the abdomen and chest, upper and lower endoscopy, endoscopic retrograde cholangiopancreatography (ERCP), and echocardiography failed to explain the bacteremia and anemia. Follow-up CT scan and Doppler sonography 9 months after placement showed TIPS was occluded. Repeat ERCP showed a bile leak with free run-off of contrast from the left hepatic duct into a vascular structure. The patient's status was upgraded for liver transplantation with Regional Review Board agreement and subsequently received a liver transplant. Gross examination of the native liver demonstrated a fistula between the left bile duct and the middle hepatic vein. Pathologic evaluation confirmed focal necrosis of the left hepatic duct communicating with an occluded TIPS and nodular regenerative hyperplasia consistent with noncirrhotic portal hypertension. Infection is rarely reported in a totally occluded TIPS. Biliary fistulas in patent TIPS have been treated by endoluminal stent graft and endoscopic sphincterotomy with biliary stent placement. Liver transplantation may be the preferred treatment if TIPS becomes infected following its complete occlusion.     

Circumferential choledochoplasties with autologous venous and arterial grafts

Circumferential choledochoplasties with vascular grafts have rarely been attempted either experimentally or in clinical practice. In this study, choledochoplasties using autologous venous and arterial grafts were performed in rats. Sixty-four rats were randomly selected into five treatment groups: A) venous interpositional graft replacement of a choledochus gap without a stent; B) venous graft with prolene stent; C) venous graft with polyethylene stent; D) arterial graft; E) a control group with simple resection between ligatures in the choledochus. The operative mortality in treatment groups B, C, D, and E, was 0, and 13% in group A. At 12 weeks follow-up, all the rats in group E had died, whereas, 52.2% (P <.05) of the rats in group A, 30% of the rats in group B, 57% of the rats in group C, and 92.8% of the rats in group D survived treatment. Surviving animals were sacrificed at 3 months for further examination. The morphology and caliber of the common bile duct of these rats were normal in 25% of the rats in group A, 33% of the rats in group B, 25% of the rats in group C, and 84.6% of the rats in group D. Proximal dilations were found in the rats presenting with abnormal morphology. The dilations were less marked in the group treated by arterial choledochoplasties. Laboratory and clinical cholestatic parameters were within normal ranges in the presence of common bile duct dilations less than four times the normal duct caliber. Electron microscopic examination of the venous and arterial graft at 3 months follow-up revealed a fibrous ring composed of collagen fibers, fibroblasts, and remnants of elastic fibers. Regenerated ductal epithelium encompassed both types of grafts. Epithelialization was more pronounced in venous grafts as compared to arterial grafts. Biliary epithelium was able to colonize the venous grafts and resume cell specialization and function as in normal biliary epithelium. The most satisfactory results were obtained using venous grafts with stents or by using arterial grafts. © 1993 Wiley-Liss Inc.     

Immediate cystic duct occlusion using an endoluminal absorbable polyglycolic acid screw

Summary Endoscopic in situ occlusion of the cystic duct and ablation of the gallbladder could constitute a useful alternative to cholecystectomy in certain patients. The purpose of this study was to examine the feasibility of endoluminal occlusion of the cystic duct using a biodegradable polyglycolic acid screw and simultaneous gallbladder mucosal ablation with a Sotradecol-ethanol mixture.Eight pigs had operative cholecystotomy. A polyglycolic acid screw was twisted into the cystic duct after the proximal cystic duct mucosa was thermally ablated using electrocautery. Cholecystography confirmed occlusion of the cystic duct. Synchronous ablation of the gallbladder mucosa was then done by instilling absolute alcohol and 2% Sotradecol. The gallbladder was drained. Animals were sacrificed on days 14, 28, and 42.All animals survived operation and showed no untoward effects. Postmortem gross inspection showed gallbladders were shrunken and surrounded with adhesions from adjacent tissue. Cholangiography and cholecystography confirmed occlusion of the cystic duct in 6 of 8 pigs (75%). Histopathologic examination showed extensive areas of mucosal necrosis mixed with small areas of epithelial regeneration.Immediate occlusion of the cystic duct is possible using an endoluminal polyglycolic acid screw.     

A Tissue-Engineered Artificial Bile Duct Grown to Resemble The Native Bile Duct

The aim of this study was to fabricate an artificial bile duct for the development of a new treatment for biliary diseases. Eighteen hybrid pigs were implanted with a bile duct organoid unit (BDOU) made of a bioabsorbable polymer. Twelve of the transplanted BDOUs had been seeded with autologous bone marrow cells (BMCs) in advance. Six animals, the controls, were grafted with the scaffold alone with no BMCs seeded. The common bile duct was cut, the hepatic cut end of the native common bile duct was anastomosed to the BDOU and the other end was anastomosed to the duodenum. The controls underwent a similar operation. The neo-bile duct was removed at pre-determined time points and investigated histologically. All 18 recipient pigs survived until their sacrifice at 6 weeks, 10 weeks or 6 months. Histological examination revealed incomplete epithelialization of the neo-bile duct at 6 weeks and 10 weeks after transplantation. At 6 months, the organoid exhibited a morphology almost identical to that of the native common bile duct. No differences were found between the controls and BMC-seeded pigs. These results show that the artificial bile duct thus fabricated can serve as a substitute for the native bile duct.     

带蒂脐静脉瓣胆道修复

目的进一步总结带蒂脐静脉瓣胆道修复的临床经验和远期随访结果。方法第一种术式，胆管上下端后壁对端吻合，前壁纵行切开，其缺损以带蒂脐静脉瓣修复21例；第二种术式，胆管狭窄切开、整形，胆管缺损以带蒂脐静脉瓣修复18例。结果本组无死亡病例。术后达7年以上25例，其中再手术3例，术后7～12年ERCP9例，双剂量静脉胆道造影1例，胆道显影均正常；轻度胆管炎2例；另10例无任何症状，B超胆道未见异常。结论带蒂脐静脉瓣胆道修复是一种理想的胆道修复手术。     

可降解外支架预防高脂血症兔自体移植静脉再狭窄

目的探讨在高脂内环境下聚乙醇酸(PGA)可降解血管外支架对自体移植静脉(VG)再狭窄的防治作用。方法建立高脂血症(HLP)兔颈内静脉-颈动脉移植模型,实验组VG应用PGA外支架保护,而对照组VG无外支架保护;分别于术前和术后4、8、12、20周获取VG,比较两组VG的再狭窄率及其内皮型一氧化氮合酶(eNOS)蛋白表达、一氧化氮(NO)生成量和组织形态变化的差异。结果对照组有4支VG出现再狭窄,而实验组无再狭窄。术后实验组VG与对照组比较:eNOS蛋白表达、NO生成量显著升高(P<0.05),脂质沉积明显减轻,内皮完整性较好,术后12、20周内、中膜增厚显著减轻(P<0.05)。结论高脂内环境下PGA外支架可有效预防VG再狭窄,作用可持续至外支架降解后。其机制与外支架保护和改善内皮功能,抑制VG的非适应性重塑有关。     

Surgical Repair of Submitral Aneurysm: A Case Report

Aim: External, non‐restrictive, macro‐porous stents prevent neointima formation in porcine vein grafts and have been proposed as a therapeutic approach to the prevention of late vein graft failure. Since these stents are non‐biodegradable and therefore may elicit deleterious long‐term, inflammatory, infective and mechanical complications the effect of external macro‐porous biodegradable (polyglactin) stents on neointimal and medial thickening in porcine vein grafts was investigated. Methods: Bilateral vein saphenous vein‐carotid artery interposition grafting was performed in Large White pigs (22–36 kg, n = 6 ) with external placement of 8 mm diameter polyglactin stents on one side, the contralateral side acting as a control. One month after surgery, graft wall dimensions were measured on histological sections using computer‐aided planimetry and immunocytochemistry undertaken for selected parameters. Results: Polyglactin stents significantly reduced medial thickening compared to the All grafts were patent at explantation. Intimal thickness was significantly lower (p < 0.05) in the stented grafts (0.11 ± 0.01 mm) compared to the unstented controls (0.18 ± 0.01 mm) . Similarly, medial thickness was significantly lower (p < 0.05) in the stented grafts (0.24 ± 0.03 mm) compared to the unstented controls (0.43 ± 0.04 mm) mm. Grafts externally supported with polyglactin had a pronounced increase in inflammatory cells (in particular, giant cells) around the biodegradable stent compared to both unstented controls and previously studied Dacron stented grafts. The space between graft and stent had become organised into a neo‐adventitia with abundant microvessels which stained positively for VEGF and lectin (markers of micorvessels and endothelial cells). Conclusions: An over‐size biodegradable stent reduces medial thickening, a component of late vein graft failure in experimental grafts. If subsequent studies confirm the preservation of this beneficial effect when the stent biodegrades completely, this form of stent may have an advantage over permanent stent material in the clinical use of external stenting to prevent vein graft thickening and failure.