Overview
Where the Problem Sits
Sound must travel through the external canal, tympanic membrane, ossicles, middle ear space, cochlea, cochlear nerve, and central auditory pathways.
Sound must travel through the external canal, tympanic membrane, ossicles, middle-ear space, cochlea, cochlear nerve, and central auditory pathways. The location of the lesion determines both the audiogram and the next clinical decision. Conductive hearing loss results from reduced transmission through the outer or middle ear. Cerumen impaction, a foreign body, otitis media with effusion, acute otitis media, tympanic membrane perforation, otosclerosis, and cholesteatoma are examples. The cochlea may still detect sound normally; the problem is getting sound to it. Sensorineural hearing loss results from injury to inner-ear hair cells, the cochlear nerve, or central auditory pathways. Presbycusis usually produces gradual, bilateral high-frequency loss. Noise exposure commonly damages cochlear hair cells and may produce a 4-kHz audiometric notch. Congenital causes, sudden idiopathic loss, and ototoxic exposure can produce other patterns. A mixed hearing loss has both components. For example, a patient with presbycusis who develops middle-ear effusion may have elevated bone-conduction thresholds as well as an air-bone gap. | Feature | Conductive loss | Sensorineural loss | |---|---|---| | Main site | Outer or middle ear | Cochlea, cochlear nerve,...