Polyurethane-Covered Self-Expandable Nitinol Stent ...

CardioVascular and Interventional Radiology

© Springer-Verlag New York, Inc. 2002 Published Online: 3 June 2002

Cardiovasc Intervent Radiol (2002) 25:381–387 DOI: 10.1007/s00270-002-0439-x

Polyurethane-Covered Self-Expandable Nitinol Stent for Malignant Biliary Obstruction: Preliminary Results Young-Min Han,1,2 Seung-Bae Hwang,1 Soo-Teik Lee,3 Jeong-Min Lee,1 Gyung-Ho Chung1 1

Department of Radiology, Chonbuk National University Medical School, 634-18, Keumam Dong, Chonju City, 560-182, South Korea Institute of Cardiovascular Research, Chonbuk National University Medical School, 634-18, Keumam Dong, Chonju City, 560-182, South Korea 3 Department of Internal Medicine, Chonbuk National University Medical School, 634-18, Keumam Dong, Chonju City, 560-182, South Korea 2

Abstract Purpose: To evaluate the immediate and long-term results in ten patients with malignant biliary obstruction using a polyurethane-covered, self-expandable nitinol stent. Methods: A nitinol stent, fully covered with high-elasticity polyurethane, with an unconstrained diameter of 10 mm and a total length of 60 – 80 mm, was placed transhepatically under fluoroscopic guidance in ten patients. The length of the biliary obstruction varied between 30 –50 mm. The follow-up examination included a clinical assessment, serum bilirubin measurement, and ultrasound examinations at onemonth intervals in all patients. Results: Initial stent deployment was successful in eight patients. Two patients experienced proximal migration, which was solved by insertion of two, uncovered Wallstents. One patient had the stent removed after two weeks because of severe nausea and vomiting. One patient had delayed migration of the covered stent after 40 weeks. The follow-up duration was 3– 40 weeks (Mean: 16.9 weeks). Seven patients died (3–26 weeks) and three patients survived (24 – 40 weeks). The bilirubin measurements in all patients had significantly decreased one week after stent insertion. The levels of amylase and lipase had did not increase after stent insertion. Conclusions: A polyurethane-covered, self-expandable nitinol stent can be used effectively and safely in the treatment of malignant biliary obstruction. The preliminary results are favorable, but there is a need for further large studies to determine both long-term survival and patency.

Correspondence to: Young-Min Han; email: [email protected]

Key words: Biliary tract, malignant obstruction—Biliary tract, interventional procedures—Prosthesis, stent The insertion of a self-expanding metal stent has become a well-accepted palliative procedure to relieve malignant biliary obstruction [1–5]. Self-expanding metallic stents have a higher patency rate and a lower complication rate than do conventional plastic stents [6]. The most common causes for stent occlusion are sludge formation, proximal and distal tumor overgrowth, tumor ingrowth, and stone formation [1, 7, 8]. Polyurethane covered Wallstents had been used in the treatment of malignant biliary obstruction, however, in some cases the covered stent was prone to premature occlusion and did not effectively prevent tumor ingrowth [9]. Recently, Nakamura et al. reported that polyurethane-covered Wallstents can be used to recanalize Wallstents obstructed by tumor ingrowth from malignant common bile duct obstruction [10]. Kanasaki et al. reported good results with polyurethane-covered nitinol Strecker stents for treatment of malignant biliary obstruction [11]. We present the results of a pilot study with fully polyurethane-covered Niti-S stents (Taewoong Medical, Seoul, Korea) in patients with malignant biliary obstruction. This is a prospective, nonrandomized study intended to determine the safety, efficacy, and performance of polyurethane-covered the Niti-S stent in clinical practice and to evaluate the clinical results obtained during the first year following stent insertion.

Materials and Methods Of the 10 patients in this study, there were four men and six women. The mean age was 62 years (range, 44 –74 years). This

study was approved by the Institutional Review Board of our University and the Ethics Committee of the Institute for Medical Science. The procedure was explained in detail to all prospective patients, and written consent was obtained prior to the procedure. Inclusion criteria were malignant obstruction of the common bile duct caused by an unresectable tumor, reocclusion of a previously self-expandable uncovered biliary stent, and obtaining witnessed informed consent. Exclusion criteria included surgical resectability, or a generally poor patient condition. The two reocclusions of previously self-expandable uncovered biliary stent occurred a Wallstent (10 mm/7 cm; Boston Scientific/Medi-tech, Watertown, MA, USA) and one Hanaro stent (10 mm/6 cm: Solco Intermed, Seoul, Korea). The Hanaro stent is described by Lee et al. [12] which is similar to Wallstent. Hanaro stent differs from the Wallstent because it is composed of only one wire. In our study, there were biopsy-confirmed adenocarcinomas in seven patients (Table 1), including pancreatic head carcinoma in three, gastric carcinoma with metastasis in two, ampulla vater carcinoma in one, and metastatic duodenal carcinoma in one patient. Three patients lacked a confirmed biopsy, but by abdominal spiral computed tomography and by percutaneous cholangiography findings. There was intrahepatic ductal carcinoma anastomotic site obstruction in one patient, pancreatic head carcinoma in one, and Bismuth type I of Klatskin tumor in one (Table 1). The stent used in this study was a self-expanding biliary Niti-S stent covered with polyurethane (Fig. 1). The polyurethane-covered Niti-S stent is a commercial product made by the Taewoong Medical Corporation. The Niti-S stent is made from 0.006 inch nitinol wire which has excellent biocompatibility and expansile force. It is a single wiring self-expandable stent without any sharp spur either end (low traumatic ends). The covering of the Niti-S stent was made by manufactures of the Taewoong Medical Corporation as below. The polyurethane covering was nonporous and stable in organic solutions such as bile. Its thickness was 0.03 mm and it was applied to the stent by dipping it in a polyurethane solution, resulting in complete coverage of the inside of the stent. To prevent stent migration, the outside of the stent was not dipped in the polyurethane solution. The stents were 6 – 8 cm long when fully expanded to the maximum diameter of 10 mm. There was a 9-French introducer system. The stent was held, compressed, and elongated on a delivery catheter by a cylindrical rolling membrane (outer sheath). The delivery catheter had three markers, one in the first-proximal portion (proximal marker), the second in the actual stent length position (stent length marker), and the last in the distal position of the loaded stent (stent marker). To release the selfexpanding stent, the outer sheath was pulled back under hydraulic support. The Niti-S stent shortened 51% after deployment; this was similar to Wallstents (50%). The stent had tungsten marker in the proximal and in the distal end that helped manipulation during deployment. Initially, a standard percutaneous transhepatic cholangiogram (PTC) with a 21-guage Chiba skinny needle (Solco intermed, Seoul, Korea) was performed under local anesthesia with 2% lidocaine HCl (Kwang Myung, Hwa Sung, Korea), and analgesia with 50 mg pethidine HCl (Myung Moon, Hwa Sung, Korea). The bile duct system was opacified with contrast medium. The length and configuration of the stenosis were documented. The obstructed biliary system was decompressed with an 8.5 or 10.2-French biliary drainage catheter (Cook Inc., Bloomington, IN, USA) in the form of external drainage. In most patients, stent placement was accomplished 2–28 days after percutaneous transhepatic biliary drainage

(PTBD). Depending on the tumor extent, a right intercostal and/or left epigastric approach was chosen. Stent insertion was performed over an extra stiff Amplatz guidewire (180 cm, 0.035 inch, curved tip; Cook Inc., Bloomington, IN, USA). Special attention was given that the covered mid-portion of the stent was located exactly at the stricture. Balloon dilation after stent insertion was not performed in any of our patients, rather an 8.5 or 10.2 French biliary drainage catheter was left in place for seven days. The biliary drainage catheter was used only for flushing and maintaining access to the biliary tree and not for drainage. Thereafter, the tubogram was repeated via the drainage catheter to check patency, function, and the stent position. The catheter was removed if free bile flow into the duodenum was documented and if the bilirubin level was normalized or markedly decreased.

Table 1. Overview of patient and treatment data No.

Age/ Sex

Imaging diagnosis

Biopsy results

Previous treatment (days)

Covered stent (mm/cm)

Two patients showed proximal stent migration immediately after insertion (Fig. 3). In these cases, we inserted a two uncovered stents which had Y-shaped configurations. One had covered distal elongation at the insertion site of the covered stent, and one had drained at a site opposite of the intrahepatic duct (IHD). One patient had requested biliary stent removal via endoscopy because she had severe nausea and vomiting before and after stent insertion. The stent did not damage the covering membrane. The other patient showed delayed migration of the covered stent after 40 weeks (Fig. 4). As this patient’s bilirubin level had also increased, percutaneous cholangiography and drainage were performed, and another uncovered Wallstent was inserted (Fig. 4). The follow-up duration of this study was 3– 40 weeks (mean 16.9 weeks). Seven patients died within three to 26 weeks, and three patients lived for 24 – 40 weeks. No cause of death was identified in any of the patients, suggesting death was due to the natural course of the disease. The patients did not show evidence of stent occlusion, such as sludge formation, proximal and distal tumor overgrowth, tumor ingrowth, or stone formation. The covered stents showed patent lumen formation in all patients; this was confirmed by laboratory findings such as bilirubin level on the last day of the study.

Discussion The reported re-obstruction rates of uncovered stents vary from 5% to 100%, with a weighted mean of 22% [13]. Some authors have tried to increase the patency-rate of biliary uncovered stents by using either iridium-192 brachytherapy, an electrolytic stent, or by coating a metal stent with an angiogenesis inhibitor [13–15]. Another way to prevent tumor ingrowth is to cover the stent with silicone or polyurethane. This method has been tested in animal studies. The main problems in animal studies are stent occlusion with debris and pus, as well as mucosal hyperplasia in the uncovered portion of the covered stent. The 24-week follow-up showed 20 – 60% stent narrowing [16]. In clinical studies, covered stents have been tried to treat malignant biliary obstruction. Many studies have had controversial results. The fully polyurethane-covered Wallstents usually are used in the treatment of malignant biliary ob-

struction. Thurnher et al. [17] reported stent migration (1/5) which occurred in one patient one day after insertion. Hausegger et al. [9] showed a 20% 30-day mortality rate in which stent occlusion occurred in eleven patients (37%; 11/30), i.e. tumor growth through the stent covering (n ⫽ 2), distal tumor ingrowth (n ⫽ 1), granulation tissue inside the stent (n ⫽ 2), and unclear etiology (n ⫽ 6). The patency rates after one, three, six, and 12 months were 96%, 69%, 47%, and 31%, respectively. Rossi et al. reported that the primary patency rates after three, six, and nine months were 72%, 46%, and 46%, respectively [18]. Seven of 22 patients with malignant biliary obstruction experienced stent occlusion, the principal cause of which was a tumor within the stent (n ⫽ 4). However, Kanasaki et al. reported that polyurethanecovered nitinol strecker stents had good results in the primary palliative treatment of malignant biliary obstruction [11]. The Niti-S stent has remarkable flexibility, elasticity, and outward radial force. The expansive power and corrosive rate were tested between the Niti-S stent and the Wallstent. The expansive power of the Niti-S polyurethane covered stent had 389 g/cm2. The expansive power of the Niti-S bare-type stent had 56 g/cm2 in 0.13 mm of wire thickness and 230 g/cm2 in 0.16 mm of wire thickness. However, the bare-type Wallstent had 77 g/cm2 of expansive power. The corrosion rate of the Niti-S stent was 1.16 ␮M/y, while the Wallstent had a 1.36 ␮M/y corrosion rate. Although made of silicone, Gore-Tex and polyurethane have been used as covering materials; polyurethane was selected as the covering material of stent as it is known to be resistant to incrustation. In addition, polyurethane easily adheres as a very thin membrane to the wire mesh of the stent [19, 20]. The use of a polyester-type polyurethane membrane, which is resistant to hydrolysis and is relatively biostable, may work as a barrier against tumor ingrowth. The other main advantage of a polyester-type polyurethane membrane is its high efficacy compared to its modest cost. It has a high resistance to chemical agents and a low coefficient of friction rate. The disadvantage of polyester is that it has lower elasticity force. It is also very difficult and expensive ane, aswire thickness

Y.-M. Han et al.: Stenting for Malignant Billiary Obstruction

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Fig. 2. 68-year-old female with metastatic duodenal carcinoma. A. Percutaneous transhepatic cholangiography demonstrates marked dilatation of the intrahepatic biliary duct and a stricture involving the distal common bile duct (lower arrow). Lesion site (upper arrow). B. Postoperative cholangiography demonstrates correct placement and sufficient expansion of the covered stent (arrows). Upper and lower margin of the polyurethane-covered self-expandable nitinol stent. C. One-week follow-up cholangiography after procedure demonstrates good passage of contrast medium into the duodenum.

Fig. 3. 68-year-old male with metastatic gastric carcinoma. A. Percutaneous transhepatic cholangiography demonstrates marked dilatation of the intrahepatic biliary duct and a stricture involving the distal common bile duct. B. The covered stent showed proximal migration immediately after stent deployment (arrows). C. Postprocedure cholangiography demonstrates one uncovered Wallstent positioned through the covered stent in the left side (arrows) and one uncovered Wallstent positioned from the intrahepatic duct to the duodenum, on the right side (arrowheads).

stent both proximally and distally. If the stenosis is of the severe focal type, stent migration into the widely dilated duct side may occur. It is possible to prevent stent migration by leaving the stent ends flared and uncovered.

The main disadvantage of this stent is that it has lower radio-opacity compared to Wallstents. However, tungsten markers in the proximal and distal ends of the stent were good indicators during the procedure.

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Fig. 4. 68-year-old female with pancreatic head carcinoma. A. Percutaneous transhepatic cholangiography demonstrates obstruction of the uncovered Hanaro biliary stent (10 mm/6 cm) in proximal portion. B. Oneweek follow-up tubogram shows good function of the covered stent (10 mm/8 cm) (arrows). C. Thirty-week follow-up of the plain abdominal film shows distal migration of the covered stent. The bilirubin level is within a normal range. D. Forty-week follow-up plain abdominal films show uncovered biliary stent. The polyurethane-covered self-expandable nitinol stent was migrated into distal and came out in evacuation. E. Percutaneous transhepatic cholangiography shows good flow of contrast medium into the Wallstent (arrows) after insertion of another uncovered stent.

Our study had some limitations, such as the small patient population. We did not confirm that the covering stents had no injury to the polyurethane membrane via cholangioscopy or autopsy. The survival duration in our patients was less than with conventional, uncovered stents. This factor however, may also depend on patients’ condition and disease process. In conclusion, our results suggest that the polyurethanecovered self-expanding Niti-S stent can be reliably and safely deployed transhepatically in the biliary system. The preliminary results are favorable, but further large studies are still needed to determine long-term patient survival and stent patency.

Acknowledgments. We thank the members of Taewoong Medical who covered the polyurethane biliary stent and provided the illustrations used in the manuscript, as well as for the information on one covered polyurethane biliary stent. We also thank Bonnie Hami, M.A. in the Department of Radiology, University Hospitals of Cleveland for her editorial assistance in the preparation of this manuscript.

References 1. Lammer J, Klein GE, Kleinert R, Hausegger K, Einspieler R (1990) Obstructive jaundice: Use of expandable metal endoprosthesis for biliary drainage. Radiology 177:789 –792 2. Salomonowitz EK, Adam A, Antonucci F, Stuckmann G, Zollikofer CL (1992) Malignant biliary obstruction treatment with self expanding stainless steel endoprostheses. Cardiovas Intervent Radiol 15:351–355 3. Gordon RL, Ring EJ, LaBerge JM, Doherty MM (1992) Malignant


4. 5.

6.

7.

8. 9. 10.

11. 12.

biliary obstruction: Treatment with metallic stents-follow-up of 50 consecutive patients. Radiology 182:697–701 Laméris JS, Stoker J, Nijs HGT, Zonderland HM, Terpstra OT, van Blankenstein M, Schütte HE (1991) Malignant biliary obstruction: percutaneous use of self-expandable stents. Radiology 179:703–707 Rossi P, Bezzi M, Rossi M, Adam A, Chetty N, Roddle ME, Iacari V, Cwikiel W, Zollikofer CL, Antonucci F, Boguth L (1994) Metallic stents in malignant biliary obstruction: Results of a multicenter European study of 240 patients. J Vasc Interv Radiol 5:279 –285 Lammer J, Hausegger KA, Flückiger F, Winkelbauer FW, Wildling R, Klein CE, Thurnher SA, Havelec L (1996) Common bile duct obstruction due to malignancy: Treatment with plastic versus metal stents. Radiology 201:167–172 Boguth L, Tatalovic S, Antonucci F, Heer M, Sulser H, Zollikofer CL (1994) Malignant biliary obstruction: Clinical and histopathologic correlation after treatment with self-expanding metal prostheses. Radiology 192:669 – 674 Hausegger KA, Kleinert R, Lammer J, Klein GE, Flückiger F (1992) Malignant biliary obstruction: Histologic findings after treatment with self-expandable stents. Radiology 185:461– 464 Hausegger KA, Thurnher S, Bodendörfer G, Zollikofer CL, Uggowitzer M, Kugler C, Lammer J (1998) Treatment of malignant biliary obstruction with polyurethane-covered Wallstents. AJR 170:403– 408 Nakamura T, Kitagawa M, Takehira Y, Yamada M, Kawasaki T, Nakamura H (2000) Polyurethane-covered Wallstents to recanalize Wallstents obstructed by tumor ingrowth from malignant common bile duct obstruction. Cardiovasc Intervent Radiol 23:161–164 Kanasaki S, Furukawa A, Kane T, Murata K (2000) Polyurethanecovered nitinol Strecker stents as primary palliative treatment of malignant biliary obstruction. Cardiovasc Intervent Radiol 23:114 –120 Lee BH, Choe DH, Lee JH, Kim KH, Chin SY (1997) Metallic stents

13.

14. 15.

16.

17.

18.

19.

20.

21.

387

in malignant biliary obstruction: prospective long-term clinical results. AJR 168:741–745 Eschelman DJ, Shapiro MJ, Bonn J, Sullivan KL, Alden ME, Hovsepian DM, Gardiner GA (1996) Malignant biliary duct obstruction: Long-term experience with Gianturco stents and combined-modality radiation therapy. Radiology 200:717–724 Cwikeil W (1996) Development of an electrolytic stent: An experimental study in rats and pigs (abstr). Cardiovasc Intervent Radiol 19:53 Machan LS, Hunter W, Arsenault L, Demetrik J (1996) Angiogensis inhibition as a means for preventing stent overgrowth (abstr). Cardiovasc Intervent Radiol 19:53 Alvarado R, Palmaz JC, Garcia OJ, Tio FO, Rees CR (1989) Evaluation of polymer-coated balloon-expandable stents in bile duct. Radiology 170:975–978 Thurnher SA, Lammer J, Thurnher MM, Winkelbauer F, Graf O, Wildling R (1996) Covered self-expanding transhepatic biliary stents: Clinical pilot study. Cardiovasc Intervent Radiol 19:10 –14 Rossi P, Bezzi M, Salvatori FM, Panzetti C, Rossi M, Pavia G (1997) Clinical experience with covered Wallstents for biliary malignancies: 23-month followup. Cardiovas Intervent Radiol 20:441– 447 Miyayama S, Matsui O, Terayama N, Tatsu H, Yamamoto T, Takashima T (1997) Covered Gianturco stents for malignant biliary obstruction: Preliminary clinical evaluation. J Vasc Interv Radiol 8:641– 648 Lammer J, Stoffer G, Petek WW, Hofler H (1986) In vitro long-term perfusion of different materials for biliary endoprostheses. Invest Radiol 21:329 –331 Hastier P, Buckley JM, Peten EP, Dumas R, Delmont J (1999) Long term treatment of biliary stricture due to chronic pancreatitis with a metallic stent. Am J Gastroenterol 94:1947–1948