Any patient known to have or suspected of having a lesion of the lateral skull base or CPA should undergo formal audiomet-ric testing. Standard testing includes air and bone conduction pure tone thresholds, speech reception threshold, and speech discrimination scores. Lesions involving the middle ear typically result in a conductive hearing loss. Audiometrically conductive hearing losses manifest as elevated air conduction thresholds compared with bone conduction threshold (air-bone gap). Sensorineural hearing loss is caused by cochlear or auditory nerve dysfunction and demonstrates air and bone conduction thresholds elevated to the same degree. Lesions that involve the auditory nerve or auditory brainstem nuclei typically result in reduced speech discrimination scores out of proportion to their effect on pure tone thresholds. Any patient found to have an asymmetric sensorineural hearing loss or reporting unilateral tinnitus should be evaluated to exclude lesions of the IAC or CPA with magnetic resonance imaging (MRI) with gadolinium enhancement.
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