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 nonhuman primate model. Design: His topathologic study. Subjects: Five macaque monkeys. Intervention: A co mmercially produced electrode array was implanted for 3 years. Results : Histologic examination demonstrated the biocompatibility of the scal a tympani electrode array. Limited soft-tissue growth and new bone gro wth were observed in the lower basal turn. There was no evidence of in tracochlear infection. Evidence of minimal insertion trauma was seen. Hair cell loss was, in general, confined to the region of the electrod e array, with normal hair cell populations toward the apex, although t here 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 th ere is substantial preservation of neural elements.