Time course and histology of urethrocutaneous fistula formation in a porcine model of urethral healing

Abstract

Objective: Urethrocutaneous fistula is a well-known complication of hypospadias surgery and is reported in 5-10% of repairs. Using a previously described juvenile pig model, we present a histological analysis of the healing of the ventral aspect of the urethral repair and describe the histological mechanism of fistula formation. Materials and Methods: Twelve juvenile pigs underwent ventral, longitudinal urethral incision and closure over a 5-French feeding tube. The ventral aspect was closed in running fashion using two closure techniques and three suture types in each animal. Three animals were sacrificed on postoperative day 3, three on day 5, three on day 12, one on day 14, and two on day 21. Closure was one-layered incorporating urethral mucosa in the animals sacrificed on days 3, 5, and 21. An extra-mucosal suture technique was used in the group sacrificed on day 12. Sections of the penis were cut, paraffin embedded, and treated with Hematoxylin and Eosin staining. Results: Fistulae were seen in 12 specimens and in association with each suture type. Fewer sections of the extra-mucosal technique showed fistulization. Fistulae lined with immature epithelium were seen by day 5. Mature fistulae were observed by day 12. Skin epithelium and urethral mucosa migrated along suture tracts. By days 12 and 21, in addition to mature fistulae, several sections showed well-healed ventral repairs with clearly extramucosal suture tracts. Conclusions: Fistula formation begins early in the healing process after ventral urethral repair. Incorporation of urethral mucosa in the ventral repair is a substrate for fistula formation with rapid migration of urethral mucosa and skin epithelium into suture tracts. The importance of a multi-layered repair and extra-mucosal suture technique are thus emphasized with respect to urethral repair. Whether the mucosal or dermal migration along suture tracts can be attenuated or prevented by changing the biochemical environment awaits further investigation. © 2003 Elsevier B.V. All rights reserved.