Local Tissue Response to Cochlear Implant Device Housings

Objective: To determine whether cochlear device housing can be a source of local tissue response in human implant recipients. Study Design: Prospective case series. Methods: Connective tissue that covered and encapsulated cochlear implants was obtained during reimplantation procedure for electronic device failure and underwent histologic analysis. Results: Fifteen devices were explanted in 10 male and 5 female subjects who had been between 15 months and 41 years of age (mean, 119.7 mo) at the time of the initial implantation. The interval between the initial and revision surgery ranged from 3 months to 11 years. Pseudocapsular formation with various degrees of chronic inflammatory reaction was present in all 15 specimens, and dystrophic microcalcifications were found in 3 of them. Foreign body birefringents were found in 9 of the 15 specimens, of which, 7 had a typical giant cell foreign body inflammatory reaction. The time between the initial and revision operations in these latter 7 patients ranged between 3 months and 8 years. All the specimens demonstrated similar histologic features in terms of pseudocapsular formation and microcalcifications, foreign body reaction, and birefringents independently of the manufacturer and type of device housing (silicone versus ceramic). Conclusion: Cochlear implants are artificial devices that can interact with the surrounding tissue in the recipient's skull. Even when the reaction to these foreign bodies is not clinically apparent, the implanted material is not absolutely innocent to the patients.