Histologic findings of silastic medialization in the canine model

Objectives: Examine the long-term histological effects of Silastic medializ ation using a canine model. Study Design: Prospective study evaluating the effects of Silastic medialization in six canine larynges, Methods: Two subj ect groups were evaluated. The first group of four dogs underwent recurrent laryngeal section followed by Silastic medialization on the paralyzed side and placement of a smaller implant on the mobile side. Two of the dogs wer e sacrificed at 9 months and two at 2 years. The second subject group consi sted of two additional dogs who underwent Silastic medialization followed b y removal of the implants at 7 months and were sacrificed 18 months later. The larynges were then processed, sectioned in the axial plane, and examine d microscopically. Results: Histological findings of both the mobile and pa ralyzed sides showed a thin (<0.5 mm) fibrous capsule surrounding the impla nt and minimal inflammatory response, Vocal fold mobility was maintained in all cases in which the recurrent laryngeal nerve was left intact. Capsule formation and inflammatory response were similar in all cases. Conclusions: Minimal tissue reactivity over a prolonged period of time suggests that lo ng-term results of Silastic medialization remain stable in paralyzed and mo bile vocal folds for up to 2 years. Similar tissue response in the subjects in which the Silastic block was removed also suggests that Silastic medial ization is a reversible procedure.