title: Covered, retrievable, expandable urethral nitinol stent: feasibility study in dogs.
abstract: OBJECTIVE
  To evaluate the feasibility of using a retrievable urethral stent and to evaluate whether granulation tissue resolves after stent removal in a canine urethra.
  
  
  METHODS
  Polyurethane-covered retrievable 0.10-mm-thick (n = 11) or 0.15-mm-thick (n = 10) nitinol wire stents were placed in the urethras of 20 dogs. In one dog, a second stent was placed in the urethra because of complete migration of the first stent into the urinary bladder. The stents were removed with retrieval hook wires 4 weeks (n = 10) and 8 weeks (n = 10) after placement. Fourteen dogs were sacrificed just after stent removal, and the other six dogs were sacrificed 2 weeks after stent removal. Information concerning procedure success, stent migration, and tissue response was obtained.
  
  
  RESULTS
  Stent placement was technically successful in all dogs. Follow-up urethrograms showed partial (n = 4) or complete (n = 1) stent migration. Stent removal failed in two dogs due to partial or complete migration. Granulation tissue was observed at both ends of the stent in 17 dogs. Urethrograms and urethral specimens obtained 2 weeks after stent removal showed diminished granulation tissue and decreased thickness of the papillary projections of the epithelium compared with results obtained immediately after stent removal.
  
  
  CONCLUSIONS
  Although some design modifications are necessary to reduce current complications, the polyurethane-covered retrievable nitinol stent seems feasible for use in the urethra. Stent-induced granulation tissue formation improved after stent removal.
authors.affiliation: Department of Radiology, University of Ulsan College of Medicine, 388-1, Poongnap-Dong, Songpa-Ku, Seoul 138-736, Korea.
authors.forename: Gi-Young
authors.initials: GY
authors.lastname: Ko
authors.forename: Gab-Cheol
authors.initials: GC
authors.lastname: Kim
authors.forename: Tae-Seok
authors.initials: TS
authors.lastname: Seo
authors.forename: Tae-Hyung
authors.initials: TH
authors.lastname: Kim
authors.forename: Jin-Oh
authors.initials: JO
authors.lastname: Lim
authors.forename: Jong-Heon
authors.initials: JH
authors.lastname: Lee
authors.forename: Ho-Young
authors.initials: HY
authors.lastname: Song
mesh_terms: D000497:Alloys; D000818:Animals; D004285:Dogs; D004867:Equipment Design; D005240:Feasibility Studies; D015607:Stents; D014521:Urethra
chemical_list: D000497:Alloys; C013616:nitinol