26 In addition, covered stents in the gastrointestinal tract may be more susceptible to food impaction while, in the bile duct, biofilms may develop in a similar way to those in plastic stents. Stents inserted into the bile duct to overcome biliary obstruction can be composed of either plastic or metal. Plastic stents become obstructed by biofilms after 2–6 months but can be readily exchanged. SEMS facilitate bile flow for a longer period but cause pressure necrosis

and pseudo-epithelialization over time and become buried within the bile duct wall.28 Because of this, the stent is very difficult to extract once it has been inserted.29 With covered stents, there have also learn more been concerns about the frequency of migration and the frequency of complications such

as cholecystitis and pancreatitis. Risks for migration are minimized by the use of stents with uncovered ends. Cholecystitis and pancreatitis can be caused by obstruction of the cystic duct and main pancreatic duct, respectively, but clinical studies indicate similar frequencies of these complications with covered stents as with uncovered stents.30 The physical properties and characteristics of biliary metal stents, colonic metal stents and gastroduodenal stents are outlined in Tables 1–3. Various esophageal stents are shown Talazoparib in Fig. 1. The Wallstent for the esophagus is made from cross-hatched stainless steel wire and exerts a strong radial force. Two models are currently available, Wallstent II and Flamingo Wallstent. The Wallstent II is covered with silicon polymer except for 2 cm on both ends while the Flamingo Wallstent is designed for use in the lower esophagus and is partially covered with polyurethane.22 The enteral Wallstent TTS (through-the-scope) has been developed for use in patients

with malignant strictures of the stomach and duodenum. Stents MCE have a length of 60–90 mm with an internal diameter of 20–22 mm. These stents have sharp metal ends and are uncovered without flares. More recently, a WallFlex enteral duodenal stent, composed of nitinol, has become available for the management of malignant strictures of the pylorus, duodenum and large intestine. The stent has blunt ends, a mid-body diameter of 25 mm and can be inserted through endoscopes with a working channel of larger than 3.7 mm. Wallstents used in the biliary system include a stainless steel uncovered stent and a nitinol stent covered with silicon. With the uncovered stent, there is substantial shortening at the time of insertion and exposed wires have the potential to damage the duodenal wall. Although tightly woven wires may limit tumor ingrowth, stents become obstructed after 4–5 months in 20–40% of patients.31,32 Whether tumor ingrowth can be further impeded by nitinol stents covered with silicon has not been determined. The Ultraflex stent used in the esophagus (Fig.