New Self-expandable Spiral Metallic Stent: Preliminary Clinical Evaluation in Malignant Biliary Obstruction PPRPOSE: To describe a new self-expandable spiral-shaped metallic stent and to evaluate its clinical efficacy in malignant biliary obstructions. PATIENTS AND METHODS: The Stent was made of a 0.01-ineh (0.25mm) stainless steel wire bent in a ziggag pattern and it was formed into a spiral configuration by differing the length of legs on each bend. One revolution was composed of 10 bends, and the stent longitudinally connected by hanging each bending point of abutting bends, without use of suture or silver solder. Twenty-six stent placed to relieve malignant biliary obstruction in 18 patients. Follow-up of 5-11 months (mean, 7 months) was obtained. RESULTS: All stents were placed in the desired location, and no procedural complications were encountered. Within 1 week after placement, all stents regained 90% or more of their original diameters. Five patients died (range,5-36 weeks), and 13 patients as still alive (range,20-45 weeks). Two patients
experienced recurrent jaundice and underwent further treatment. The stent wag easily inserted, expanded well, was flexible, could be repositioned, and did not shorten. CONCLUSION: Favorable clinical results were obtained with this spiral stent in malignant biliary obstruction, and further clinical testing is warranted Since 1985, when Carrasco et al (1) used intraluminal metallic stents in the biliary system in an animal model, various types of metallic stents have been designed and used for vascular and nonvascular strictures. Over the past few fears, man artieles have reported good results with use of metallie stents, especially in biliary obstruction (2-21). Several problems, however, have still been reported concerning commercially available metallic stents. The Wallstent device (Bchneider, Buelach, Switzerland) shortens considerably after expansion. The Gianturco-Rosch Z stent (Cook, Bloomington, Ind) has wide interspaees, which theoretically increase the prevalence of blockage in malignant obstruction due to tumor ingrowth, and has weak radial force at the connected portion (22). To overcome these problems, we designed a new type of self-expandable spiralshaped metallic stent and report clinical results in patients with malignant biliary obstruction. PATIENTS AND METHODS Stent A new spiral stent was made of a 0.01-ineh (0.25-mm) stainless steel wire bent in a zigzag pattern with alternating leg lengths; the longer leg was 8 mm in length, and the shorter leg was 7.2 mm. One revolution consisted of 10 bends, farming a spiral cylindric configuration (Fig 1). Each bending point twas a 5" torsion angle that alternated direction to prevent distortion at each connecting point caused by hanging the abutting caudal bend. The stent was longitudinally connected by hanging he cephalic bending points of distal egment on the corresponding caudal bending points of proximal segment. That is, the cephalic bending point of the 11th bend was hung on the caudal bending point of the thirst bend, and the 12th bend on the second bend, in that order (Fig 2). The stent was 10 mm in fully expanded
diameter, and the length wart variable. The stent was construected with only one wire, without use of silver solder or suture for connection. To prevent twisting and overlapping of the stent, both ends of wire were used as struts, which traversed each segment obliquely, and were firmed to the bend of the opposite segment. The stents were made by hand and were not commercially manufactuned. These are, however, now available commercially (Sooho Meditech, Seoul, Korea). The research protocol was approved by the Hospital Institutional Review Committee, and all patients signed an experimental subject consent farm. Patients Between September 1993 and July 1994,26 self-expandable spiral metallic stents were placed in 18 consecutive patients with unreseetable malignant biliary obstruction. Patients ranged in age from 34 to 73 years(mean,58 years) and included 10 men and eight women (Table).
The causes of obstruction were hi-lar cholangiocarcinoma in eight patients, common bile duct (CBD) carcinoma in five, gallbladder carcinoma in one, pancreatic carcinoma in three, and metastasis from rectal carcinoma in one. The diagnoses were pathologically proved with surgery in seven patients, percutaneous needle aspiration in four, bile cytology in three, and biopsy through a percutaneous transhepatic biliary drainage (PTBD) tube in four. The site of obstruction was the hilar portion in eight patients and the CBD in 10. One patient with recurrentjaundice, which developed 13 mouths after placement of a Giantureo stent, was included in this study (patient 1 in Table). In this case, ingrowing tumor was pathologically proved to be papillary carciroma of the CBD with biopsy through a PTBD tube. Figure 4. Method of retrieving the deployed stent. (a) A puree-string suture is placed through the caudal bend of the tail stent and runs through the positioner. (b) The positioner is advanced, and the bends of the tail stent are gathered. (c) The sheath is advanced overthe stent.
Technique All patients had undergone PTBD under fluoroscopic guidance, and the stents were placed 3-5 days after the initial drainage procedure. Before stent insertion, cholangiograms were obtained through an external drainage tube to evaluate the level and length of biliary obstruction. The stents were inserted through the right intrahepatic duct in nine patients, the left intrahepatic duct in one, and the bilateral transhepatic route in eight (Fig 3).
The technique of stent placement was the same as that far the GianturcoRosch Z stent, and it has been previously described in detail (7-10). For stent delivery, we used an 8.5-F Gianturco-Rosch biliary Z stent introducer set (Cook). The introducer sheath was placed across the desired deployment site in the bile duct, and the compressed stent was pushed by the positioned. When the stent was in the proper
position, the positioned was fixed and the sheath was withdrawn to expose the stent and allow it to expand. If the stent is malpositioned, it can, be relocated or retrieved easily. The method of relocation or retrieval is similar to that uses with the stent described by Irie et at (23). To be able to relocate the malpositioned stent, before the stent is inserted into the introducing sheath, a parse-string suture is run through the caudal bend of the stent tail and the positioner. If relocation is necessary after stent deployment, the positioned is advanced to the caudal end of the stent, the holding suture is pulled to compress the caudal bend of the stent, and the stent is retracted by advancing the sheath over it. The stent can now be retrieved by pulling the holding future or relocated by moving the sheath to a new position. After replacement, one limb of the retention loop is withdrawn out of the positioner (Fig 4). Antibiotics were administered intravenously to all patients prior to procedure, and intravenous analgesics (Demerol [meperidine hydroehloride]: Sanofi Winthrop Pharmaceuticals, New York, NY) were given to two patients who experienced pain during tine procedure. Balloon dilation of stenotic segments was not performed prior to stent insertion, and we chose a stent that twas at leasts 2 cm longer than the obstructed segment. The length of stent uses ranged from 7 to 13 cm (mean,8.3 cm). After stent placement, a 5-F external drainage catheter remained within the stent to monitor continued stent patency. Follow-up cholangiograms were obtained through the external drainage catheter on the 3rd and 7th day after placement. Plain abdominal radiography was used to evaluate the position and the degree of expansion of the stents. We analyzed the time course of stent expansion on follow-up image and monitored serum bilirubin leve to evaluate the effects on jaundice. RESULTS Initial stent placement was successful in all patients without need for repositioning or retrieval. No major complications were encountered during or after stent insertion. One patient with gallbladder carcinoma, who had undergone placement of two stents by means of bilateral transhepatic approaches,
also underwent intraluminal iridium-192 radiation therapy. Of 18 patients, five have died (range,5-36 weeks) and the remaining 13 patients are still alive (range, 20-45 Weeks).Two Patients developed recurrent jaundiee and underwent PTBD. The time lag between stent insertion and recurrent jaundice was 35 weeks and 19 weeks (Table). The cause of reocclusion was tumor ingrowth in the former and tumor overgrowth in the latter. One patient (patient 1 in Table) who developed reocelusion due to tumor ingrowth had a papillary carcinoma of the CBD, which tends to grow intraluminally rather than to extend longitudinaliy. Initial serum bilirubin levels ranged from 11.5 to 44.3 ntg/dl (197-7587mol/L)(mean, 23.4mg/dL(400mol/L); normal, <1.4 mg/dl [23.9mol/L]). After stent insertion values returned to the normal range in all patients. All of the inserted stents regaine, 90% or more of their original diameter within a week after placement and showed no shortening after ex- pansion. Three stents placed across the papilla of vater showed no problems such as erosion or ulceration of duodenal mucosa, which was confirmed with endoscopy during the follow-up period (Fig 5). The stent plaeed in a curved area maintained its flexibility without de crease in luminal diameter.
DISCUSSI0N Recently, various metallic stents have been introduced and used in the biliary system, they are variations of three major stent tapes. These are the Giantureo Z stent, the Wallstent, and the Streeker stent (Meditech/Boston Scientific, Watertown, Mass). While all three types of metallic stents are constructed of a
thin, wire-type material, they differ in wire composition, shape, and delivery method. For these reasons, they have diffarent characteristics.the Wallstent is made of stainless steel wires woven into a tubular mesh, The stent is compressed by a rolling membrane, which is removed during insertion. It erin be introduced through a 7-F sheath, the smallest diameter among available stents, and has narrow interspaces, lessening the occlusion rate due to tumor ingrowth. However, shortening after expansion (32%-40% shortening of initial length) and less radiopacity make adequate placement diffcult (5,6,15). It has been reported that duodenal ulceration and CBD perferation are caused by sharp wires on both ends of the stent (6). The Strecker stent is a balloonexpandable device made of tantalum wire. It hart superior flexibility and radiopaeity. On the other hand, because it has less self-expansibility, it is less desirable to usa the strecker stent in cases with rigid obstruction such as metastatic Iymphadenopathy. A 10-F introducing sheath is required due to the size of the deflated balloon, and shortening is shown after placement (19% shortening of initial fength) (7). The Gianturco Z stent is self-expandable and is constructed of fine Stainless steel wire with a zigzag configuration. It has good expansibility and shows no shortening after expansion. In the original design, individual bodied are connected by additional straight struts with soldering. Therefore, it has some limitations in curved lesions. In the modified design, six bands are tied with a nylon Buture that Passes through eyelets at the end of each bend to farm a cylinder.twelve eyelets located at the connected portion limit increases in number of bends, resulting in wide interspace, and limit decreased in the diameter of the introducer. It has lower expandable force in areas of connections be tween individual stent bodies. Also, it is difficult to push the stent with multiple bodied through the introducer due to overlapping at connected portion, especially in patient wish an angled tract. The inability to relocate the stent in cases of stent malposition and high costs are problems in all tapes of stents. Irie et at (23) designed a relocatable Gianturco-type expandable stent to replace malpositioned stent after placement but could not overcome the basic problems of the Z stent. We believe that an optimal stent should meet the following requirements: (a) be compressible and require only a small introducer, (b) have enough expansibility to expand the stricture segment and have
uniform expansibility throughout it entire length, (e) be easily delivered. (d) be radiopaque and well seen during delivery and positioning, (e) have narrow interspaces to prevent tumor ingrowth, (f) keep its length and not shorten after expansion, (g) be flexible and adjusts to a curved tract, and (h) be legs expensive. To solve some of the problems associated with the Giantureo Z stent. Maeda et at (24) firsts developed a spiral-shapes Z stent, and Nakamura et al (25) reported results of transjugular intrahepatic portosystemic shunt placement in an experimental model with use of a spiral stent. Their stent has uniform expansile farce throughout its effective length, good compressibility, and good stability. In their spiral stent, however, because one revolution consists of six bends, it has wide interspaces between leg wires, which is not considered suitable for use in malignant obstruction. On the contrary, as our stent was connected by a "hanging method" without using eyelets and suture, and was eomposed of 10 bends in one revolution, we could narrow the interspace as well as achieve uniformity in expansile force throughout the ontire length of the stent. Cragg et at (26) designed other type of spinal stent, which differed from that of Maeda et al in wire component (nitinol) and suture configuration (interrupted fashion). However, it is doubtful that their preclinical results in vascular system can be applied to the human biliafy system. We found that our new stent fulfilled all the aforementioned requirements in our experience. Firat it bas adequate compressibility. The 10-mm-diameter stent could be easily delivered through a 8.5-F sheath. Second, it has enough expansibility to relieve malignant obstruction an has better radiopacity than the Wallstent. Third, we could narrow the interspace by eliminating the eyelets and increasing the number of leg bendy. Fourth, it shown no shortening in length after expansion. Fifth, our stent kept its cylindrieal lumen in curved portions of the bile duct without decreasing its luminal diameter, because each segment was connected in a hanging fashion and was not fried. Finally, our spinal stent can be retrieved and relocated immediately after placement. Recently, Rossi et at (27) reported their multieenter clinical study concerning patency of
various tapes of metallic stents in 240 patients with malignant biliary obstruction. In their study, the 25- week patency rates were 78% for the nitinol Strecker stents,67% for the Wallstents,30% for the Z stents, and 20% for the tantalun Strecker stents. The 50-week patency rates were 68%,51%,0%, and 15% or less, respectively. Average patency was 8.3,5.9,2.3, and 4.0 months, respectively. In our clinical trials, the patency rate of this new stent was not worse than that of the other metallic stents. In conclusion, we obtained favorable clinical results with this new spiral stent in patients wish malignant biliary obstruetions. We believe that our stent may be premising for clinical Use. Aclmowledgments: We thank Mi Jae Lee and Young Soo Lee far assistance in our stent placement procedure, Sung Boon An, Jae Yong Lee, and Buk Jae Lee at Sooho Medi-tech far manufacturing the stent. References 1. Carrasco CH, Wallace S, Charnsangavej C, et al. Expandable biliary endoprosthesis: an experimental study. AJR 1985; 145:1279-1281. 2. McLean GK Burke DR. Role of endoprostheses in the management of malignant biliary obstruction. Ra- diology 1989; 10:961-967. 3. Mueller PR, Damson SL. Metallic biliary endoprostheses and biliary stricture dilation. Syllabus: a diag- nostic categorical course in interventional radiology. Oak Brook, III: Radiological Society of North America,1991; 111-118. 4. Lammer J, Klein GE, Kleinert R, Hausegger K, Einspieler R. Obstructive jaundice: use of expandable metal endoprosthesis for biliary drainage. Radiology 1990; 177:789-792.
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