Covered self-expandable metal stent (C-CSEMS) has the risk of obstruction of the cystic duct, and the main and branch pancreatic ducts due to strong radial force and covering material, which results in cholecystitis and pancreatitis.~A flower-type covered self-expandable metal stent (F-CSEMS) having a five-petal-shaped design with side grooves was constructed to prevent the obstruction of the cystic duct orifice.~This study investigated the value of the F-CSEMS in protection for cholecystitis and pancreatitis.~The investigators will enroll patients with distal MBO (Malignant Biliary Obstruction) who received placement at the Samsung Medical Center. Transpapillary flower-type covered self-expandable metal stent (F-CSEMS) placements will be included in this study.~The diagnosis of MBO will be based on imaging and/or pathological findings. Malignancy was proved by histopathological confirmation obtained by endoscopic ultrasonography-guided fine-needle aspiration (EUS-FNA), bile duct biopsy (cytology), pancreatic duct cytology, or liver biopsy.~The investigators will evaluate the frequency of pancreatitis and cholecystitis.~Furthermore, the investigators will evaluate various parameters to clarify the predictive factors of pancreatitis and cholecystitis. The following 10 variables will be evaluated in pancreatitis by univariate analysis: [1] sex, [2] age, [3] primary disease, [4] Covered type (partially or fully), [5] SEMS with high AF, [6] F-CSEMS with high RF, [7] EST before F-CSEMS, [8] previous biliary stent, [9] contrast injection into the pancreatic duct (pancreatogram), and [10] the position of the distal stent edge.~The following 11 variables will be evaluated in cholecystitis by univariate analysis: [1] sex, [2] age, [3] regions of stricture, [4] F-CSEMS with high AF AF (axial force), [5] F-CSEMS with high RF, [6] previous biliary stent, [7] gallbladder stone, [8] contrast injection into the gallbladder (GB injection), [9] involvement to the orifice of the cystic duct (OCD), [10] position of distal stent edge, and [11] cystic duct occlusion by F-CSEMS.~--------------------------------------------------------------------------------------------------------~software: nQuery + nTerim (version 4.0)~- One-sided Chi-square test for proportion comparison~H0: p1=p2 vs H1: p1>p2 (The incidence of complications in the flower-type covered stent is smaller than in the conventional stent.)~p1 = incident rate of complication in full covered stent group p2 = incident rate of complication in flower-type covered stent group~Set p1(incident rate of complication in full covered stent group) = 15% = 0.15~expected % decrement in incidence rate = 40%, 50%, 60%, 70% --> p2 = 0.09, 0.075, 0.06, 0.045~Significance level (alpha) = 0.05~Maximum number of patients who can be enrolled = 10 per month at SMC = 120 per year~Expected enroll period = 1 year = 12 months~Sample size calculation with targeted power of 80% Expected % decrement in incidence rate 70% p2 4.5% Required n per group 116 Required total sample size 232 Required enroll period (year) 1.9~Power calculation with a total sample size of 232 (116 per group) Expected % decrement in incidence rate 40% 50% 60% 70% p2 9.0% 7.5% 6.0% 4.5% Expected power (%) 32 48 64 80~Minimum % decrement to be detected with power of 80% Planned enroll period (year) 1 1.5 2 2.5 3 Enroll-able n per group 60 90 120 150 180 Enroll-able total sample size 120 180 240 300 360 Minimum % decrement to be detected 93.33% 78.70% 68.70% 62.70% 58.00% Expected p2 1.0% 3.2% 4.7% 5.6% 6.3%
The aim of this animal study is determining the technical feasibility of the novel flower-type covered self-expandable metal stent (F-CSEMS) and investigating whether the novel flower-type covered self-expandable metal stent (F-CSEMS) could prevent cholecystitis and pancreatitis, comparing with conventional covered self-expandable metal stent (C-CSEMS).