Electrocochleography in deaf subjects.

Electrocochleography using the transtympanic electrode technique was performed on 86 deaf ears. Auditory nerve action potential was detected in 9 ears, in 5 of which deafness was caused by cerebellopontine angle tumor or surgery. A low threshold of the cochlear microphonics' response was also observed in some of the cases with deafness caused by mumps or cerebellopontine angle tumor. Various pathophysiological states of the inner ear can be observed, even in cases showing the same total deafness when measured by audiometer.