Cochlear histopathologic characteristics following long-term implantation. Safety studies in the young monkey.

OBJECTIVE: To evaluate the safety of cochlear implantation in children 2 years of age or younger using a non-human primate model. DESIGN: Histopathologic study. SUBJECTS: Five macaque monkeys. INTERVENTION: A commercially produced electrode array was implanted for 3 years. RESULTS: Histologic examination demonstrated the biocompatibility of the scala tympani electrode array. Limited soft-tissue growth and new bone growth were observed in the lower basal turn. There was no evidence of intracochlear infection. Evidence of minimal insertion trauma was seen. Hair cell loss was, in general, confined to the region of the electrode array, with normal hair cell populations toward the apex, although there was evidence of hair cell preservation adjacent to the array. At least 20% of spiral ganglion cells were preserved even in regions with a smaller proportion of hair cells. CONCLUSIONS: Even after extended periods of implantation, the electrode array is well tolerated, and there is substantial preservation of neural elements.