Development of Biliary Self-Expandable Metal Stents for Pancreatic Cancer and Cholangiocarcinoma

The axial force and the radial force are important parameters of metal stents. An axial force is the strength that acts to return a self-expandable metal stent placed in a bent position to a straight position, and radial force is the strength with which the stent expands a bile-duct stricture in the centrifugal direction. In general, stents with weak axial force and strong radial force are considered ideal. Four types of stents are used to treat pancreatobiliary diseases: (1) distal bile-duct stenosis, (2) hilar bile-duct stenosis, (3) pancreatic pseudocyst, and (4) endoscopic ultrasound-guided hepaticogastrostomy. (1) Distal biliary obstruction is the most common indication, for which many types of stents are available. (2) Stent-in-stent and side-by-side placement of dedicated metal stents are used for hilar biliary obstruction. (3) Lumen-apposing metal stents, with a large-diameter lumen, are used for pancreatic pseudocyst and for endoscopic necrosectomy. (4) Stents dedicated to EUS-guided hepaticogastrostomy have also been developed and some have features that prevent their migration into the peritoneal cavity.