Histological Changes in the Bile Duct after Long-Term Placement of a Fully Covered Self-Expandable Metal Stent within a Common Bile Duct: A Canine Study

BACKGROUND/AIMS: To date, it has been difficult to determine the optimal stenting duration of a fully covered self-expandable metal stent (FCSEMS) in a benign biliary stricture. The purpose of this study was to identify the histopathological changes in a bile duct resulting from long-term placement of a FCSEMS. METHODS: An FCSEMS was inserted into the common bile duct of 12 canines, and the animals were divided into four groups. Posteuthanasia, necropsy was performed to examine the histopathological changes in the bile ducts after 1, 3, 6, and 9 months. RESULTS: The results of necropsy showed that the covered membranes of the FCSEMSs were intact and easily removed from the bile ducts in 11 of the canines. Severe epithelial hyperplasia of the stented bile duct and epithelial ingrowth into the stent occurred in one animal (from the 3-month group). On histopathological examination, mild inflammatory changes were observed in the stented bile ducts, and there was no significant difference between the four groups. Among the 12 animals, five had de novo stricture. CONCLUSIONS: An FCSEMS can be inserted into the bile duct without severe histopathological changes up until 9 months. However, a de novo stricture and severe epithelial hyperplasia relating to the stent insertion might occur.