Spiral Ganglion Cell Loss Is Unrelated to Segmental Cochlear Sensory System Degeneration in Humans

Objective: To demonstrate that contrary to what occurs in animals, neuron loss in the human spiral ganglion is not in proportion to organ of Corti hair or supporting cell loss. Study Design: Histopathological review of archival temporal bone histological sections. Setting: Nonprofit research facility. Methods: Four temporal bones, from an archival collection of 1,448 temporal bones, were found that had a total loss of hair and supporting cells limited to the basal segment of the cochlea and a hearing loss of 3 or more years (range, 3-28 yr). Cochlear reconstructions were conducted to demonstrate the populations of hair and supporting cells, peripheral processes (dendrites), spiral ganglion cells, and the amount of surviving stria vascularis in different cochlear segments. Results: The total loss of hair and supporting cells of the organ of Corti in the base of the cochlea is not accompanied by a proportional loss of spiral ganglion cells in the modiolar base. Conclusion: A long-term loss of hearing in frequencies greater than 2 kHz, and corresponding hair cell loss, does not result in a subsequent loss of spiral ganglion cells in humans, in contrast to what has been reported in association with animals. These findings suggest that the poor performance of cochlear implant in patients after prolonged deafness is not caused by ongoing degeneration of ganglion cells.