[Cochlear implants: histological data].

We have performed a histological examination of the pars petrosa of 13 implanted patients. Morphological data were confronted with the clinical findings. The results of this study show that the nerve elements stimulated by the electrode are the cells of the spiral ganglion, and that a small number of ganglionic cells, as few as 10% of the normal figure, is compatible with auditory perception by electrical stimulation. Furthermore, all the implanted pars petrosa were the seat of a fibrosis and neo-ossification reaction around and sometimes even beyond the tip of the electrode. The trauma caused by the insertion of the electrode into the cochlea involved the sensorial cells of the organ of Corti and the dendritic populations in the lamina spiralis, but the cells of the spiral ganglion were spared. Prolonged electrical stimulation (14 years in 1 case) does not appear to have any deleterious effect on the survival of the spiral ganglion, of the cochlear nerve or of the cochlear nucleus.