Localization of endotoxin in the inner ear following inoculation into the middle ear

Sensorineural hearing loss is known to be a significant sequela of otitis media (OM). The pathophysiology of such hearing loss in OM is thought to be due to transmission of toxins and other bacterial products through the round window membrane, damaging the hair cells of the basal turn of the cochlea. Other routes, such as those involving the oval window, blood vessels and lymphatics, may also be involved. The purpose of this study was to elucidate the routes from the middle ear cavity to the inner ear and also the distribution pattern of endotoxin in the inner ear after injection of fluorescence-labelled endotoxin into the tympanic cavity and detection of fluorescence in the cochleae, vestibular end organs and facial nerves. This fluorescence was far more intense in the lower turns of the cochlea. These findings suggest that endotoxin can reach the inner ear by various routes, e. g. the round window, blood vessels or lymphatics, and/or interscala exchange, resulting in a disturbance not only of the cochlea but also of the vestibular end organs.