ABNORMAL ELECTROCOCHLEOGRAPHY AFTER EXCISION OF ACOUSTIC NEUROMA

Pre-, per- and post-operative ECoG findings obtained from a 43-year-ol d woman with an acoustic neuroma were studied. Although CAP presented a normal waveform in response to click during the whole process of the operation, it was transformed into an abnormally broadened negative w aveform in shape with a mild hearing exacerbation, and has remained un changed up to the present. This broad response was considered to be a receptor potential, because it showed no adaptational amplitude reduct ion. Additionally, postoperative ECoG to tone burst stimuli demonstrat ed an increase in DC potential following the stimulus envelope. Conseq uently, the broad negative response to click was considered to be main ly composed of an enlarged negative SP. The generation mechanism under lying the phenomenon of an abnormally increased negative SP found afte r the excision of an acoustic neuroma is discussed, with reference to several items in the literature. Similar responses in the postoperativ e ECoG of patients with acoustic neuromas obtained by us in the past w ere given as additional examples. CAP as an indicator for intraoperati ve monitoring can hardly predict postoperative auditory function. It i s to be hoped that a more reliable auditory monitoring method during t he operation will be established.