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Background and study aims: Various mechanical properties of self-expandable metallic stents (SEMSs) have been reported. They can be classified into the device behavior during and after deployment. While there have been several reports on the latter, information on the former is insufficient. During deployment, the position is maintained by retracting the delivery catheter. We propose that this pulling force be called the traction force and that the magnitude of traction force is termed the traction momentum. The aim of this study was to measure these parameters in order to clarify the properties of SEMSs in terms of their deployment. Material and methods: The traction force, traction momentum, and shortening rate of 10 different SEMSs were measured. Traction force was measured using in-house equipment, and the shortening rate was determined by measuring the stents. Results: The shortening rate was closely related to the stent structure. The traction force varied between 1.5 N and 9.4 N, and the traction momentum was significantly elevated in covered and braided stents. A high traction force did not imply a high traction momentum. Conclusions: A low or constant traction force and a minimal shortening rate significantly facilitated SEMS deployment to optimal positions. Traction force could be an important element for new ideal SEMS design.

Endoscopic transpapillary gallbladder stenting is currently indicated to treat acute cholecystitis, and a double-pigtail plastic stent is usually placed [1–3]. No case of cholecystocolonic fistula caused by endoscopic transpapillary gallbladder stenting has been reported. An 87-year-old man was admitted to our hospital for the treatment of right hypochondralgia. Computed tomography revealed gallbladder distension and wall thickening (●" Fig.1). Magnetic resonance cholangiopancreatography revealed a gallstone in the neck of the gallbladder. Percutaneous transhepatic gallbladder drainage was contraindicated because of anatomical inaccessibility, and endoscopic naso-gallbladder drainage was associated with a risk for tube removal by the patient. Therefore, we performed endoscopic transpapillary gallbladder stenting with a double-pigtail stent (CX-T stent, 7Fr×12cm; Gadelius Medical K.K., Tokyo, Japan) (●" Fig.2). The acute cholecystitis resolved after endoscopic transpapillary gallbladder stenting, and the patient was discharged without a cholecystectomy or removal of the plastic stent. After 18months, the patient was readmitted with recurrent right hypochondralgia. Computed tomography revealed fat stranding around the gallbladder and showed the proximal pigtail to be located in the colonic lumen (●" Fig.3). At emergency surgery, we found the colon adherent to the gallbladder, which was affected by acute cholecystitis; in addition, the proximal pigtail had penetrated the walls of both the gallbladder body and the transverse colon (●" Fig.4). The patient underwent an emergency cholecystectomy and partial colectomy; the final diagnosis was acute cholecystitis associated with cholecystocolonic fistula, caused by the plastic stent. Endoscopic transpapillary gallbladder drainage is preferred in patients in whom percutaneous transhepatic gallbladder drainage is contraindicated, such as those who have severe coagulopathy or thrombocytopenia, or in whom the lesion is anatomically inaccessible [3]. Long-term placement of a gallbladder stent is used to prevent the recurrence of acute cholecystitis [1]. It is wise to remember that a cholecystocolonic fistula is one possible adverse event after endoscopic transpapillary gallbladder stenting, even when a double-pigtail plastic stent has been used.

Covered self-expandable metal stents (SEMS) occasionally migrate [1], and various techniques for their removal have been reported [2–5]. However, the use of a scissors forceps for the endoscopic removal of a distally migrated SEMS that has adhered to the duodenal mucosa has not been previously reported. An 82-year-old man was admitted to our hospital because of cancer of the pancreatic head with liver metastasis. We inserted a fully covered, 10×60-mm WallFlex stent (Boston Scientific, Natick, Massachusetts, USA) across the duodenal papilla. The patient was readmitted because of the passage of tarry stool 1 year after insertion of the SEMS. Duodenal endoscopy revealed tumor invasion of the duodenum and distal migration of the SEMS, which adhered to the duodenal mucosa (●" Fig.1). We attempted to remove the SEMS by grasping the body of the stent with a large, mounted rat-tooth forceps. The proximal end of the SEMS was removed from the common bile duct. However, the distal end of the SEMS could not be removed because it strongly adhered to the duodenal mucosa (●" Fig.2). The distal wire loop (retriever loop) was covered by the duodenal mucosa as a result of epithelial hyperplasia, which had caused a mucosal bridge to form (●" Fig.3), and partial mucosal ulceration was observed. Therefore, we used a scissors forceps (FS-5U-1; Olympus Optical Co., Tokyo, Japan) to cut the wire loop (●" Fig.4). After the wire loop had been successfully cut (●" Fig.5), the SEMS was easily removed from the duodenal mucosa, and ulceration was evident (●" Fig.6). Argon plasma coagulation (APC) is reportedly a useful procedure for cutting a SEMS [5]; however, APC of the wire loop of a SEMS located close to a site of duodenal ulceration may cause duodenal perforation. In contrast, when a scissors forceps is used, there is no risk for perforation, and cutting with a scissors forceps may be a useful technique in these situations.