[Temporal bone histopathology of noise-induced hearing loss]

To examine the relationship between hearing and changes in the inner ear, we investigated human temporal bone specimens from 2 patients with noise-induced hearing loss and prepared audio-cytocochleograms as described by Schuknecht et al. Patient 1 was a 50-year-old male who died of thyroid cancer and had worked at a printing house for 38 years. Patient 2 was a 58-year old male who died of maxillary sinus cancer and had worked in construction for 22 years. A pure-tone audiogram showed high-tone sensorineural hearing loss with c5-dip-type hearing disorder in both ears in Patient 1, and a high-tone abrupt form of sensorineural hearing loss in Patient 2. Pathological examination of the temporal bone revealed degeneration and disappearance of the organ of Corti at the basal turn and disappearance of cochlear neurons in both patients. Audio-cytocochleograms revealed hearing disorder consistent with the changes in the inner ear in both patients. Marked degeneration and disappearance of the organ of Corti and stria vascularis were present in patient 1. It is generally known that disorders of the organ of Corti for a long period is involved in the etiology of noise-induced hearing loss. This degeneration of the organ of Corti is produced at a basilar membrane with the maximum amplitude related to exposure to noise according to a physical and mechanical factors. Moreover, animal experiments have shown that exposure to noise decrease cochlear blood flow. In Patient 1 both the organ of Corti and the stria vascularis exhibited degeneration, suggesting that not only physical and mechanical factors but a cochlear circulatory disorder related to exposure to noise was involved in the etiology of the pathological changes in the temporal bone related to noise-induced hearing loss.