Coated v noncoated ureteral metal stents: An experimental model

Purpose: The purpose of the present study was to compare the standard metal stents with internally and externally coated metal stents in the pig model . Materials and Methods: In nine female pigs weighing between 25 and 30 kg, t he metal stents were randomly placed in either the right or left ureter, fo r a total of 18 stented ureters. Six ureters were stented with a Wall-stent (Schneider, Zurich, Switzerland), six with a Passager stent (Boston Scient ific, Natick, MA, USA), and six with a Corvita endoluminal graft (CEG) (Bos ton Scientific, Natick, TMA, USA). Patency was examined by nephrostotomogra phy 24 hours and 21 days after the initial procedure. Results: Free flow of urine through the stents into the bladder was reveale d in all ureters with the exemption of four cases where a Passager stent mi grated into the bladder, jeopardizing ureteral patency. The Wall-stent gene rated mild inflammation with metaplasia of the urothelium; the CEG a more p ronounced inflammatory response in the adjacent ureter; and the Passager st ent severe inflammatory reaction with necrosis of the urothelium. The secti ons of the Wall-stents revealed the presence of a mild polypoid reaction ad herent to the internal surface of the devices. The coated stents showed no tissue ingrowth through the lining material into the ureteral lumen, and th us, the urothelium was compressed beneath the prostheses. Conclusions: Our experimental results suggest that the standard Wall-stent generates less inflammation of the surrounding tissues than coated stents. The coated stents have the advantage of minimal tissue ingrowth but have a tendency to migrate toward the bladder.