Modiolar microexostoses with neural impingement and hearing loss in guinea pigs.
Sensorineural hearing loss resulting from auditory nerve impingement due to temporal bone abnormalities may occur in patients with osteitis deformans, osteopetrosis, other osseous abiodystrophies, and aging. In experimental animals, vitamin A deficiency and normal aging may result in temporal bone abnormalities; however, these bony changes have not been associated with sensorineural hearing loss. In assessing 27 Hartley guinea pigs prior to ototoxicity studies, two 33-week-old female animals, when tested for Pryer reflex and brainstem auditory-evoked responses, were found to have severe bilateral sensorineural hearing loss. Histologic studies of temporal bones from these animals showed marked abnormalities. The cochleas demonstrated accumulations of osteoid and newly formed bone in the modioli that extended along the osseous spiral laminae with irregular bony projections appearing as microexostoses, which at times bulged into the scala tympani and involved the basilar membrane. There was also neuronal depopulation and decreased dendrites associated with the bony impingement. The findings in these guinea pigs suggest a familial disease characterized by abnormal bone formation in the cochlea resulting in neural impingement and sensorineural deafness.