[The promontory test and electrocochleography with reference to indications for cochlear implant]

A successful cochlear implant demands a functioning auditory nerve. A subjective and qualitative recording can be obtained by promontory testing (PT) whereas cochlear microphonics (CM) give information about the status of the hair-cells in the inner ear. The results of both tests together show different patterns: in sensory deafness in which a cochlear implant is indicated, no CM and no compound action potentials (CAP) can be obtained, whereas the patient reports hearing sensations (PT positive) in response to promontory testing. Deafness caused by lesions close to the second neurone of the auditory pathways can be localized by preserved CM and CAP, but there is no response to promontory testing. A ganglionic deafness ie. of the first neurone can be distinguished by preserved CM, absent CAP and a negative PT. The combined results of electrocochleography and promontory testing help in deciding whether a cochlear implant is indicated, and in localising the origin of the deafness, eg. neural or sensorineural. The possible results are illustrated by examples.