Transtympanic electrocochleography in the diagnosis of retrocochlear tumours.

Transtympanic electrocochleography has been used as a diagnostic procedure in over 250 adult patients with sensorineural deafness. No complications have been encountered. Among these patients vestibulocochlear Schwannoma (acoustic neuroma) has been confirmed in 56 ears while 11 other ears have been found to be affected by other space-occupying lesions. As a result of our observations in these patients, we would like to propose that there are at least three separate criteria to be considered in reaching or strongly suspecting a diagnosis of such pathology. These are broadening of the action potential (loss of P1), observation of a clear microphonic response, and preservation of the action potential even when using stimulus intensities which are not audible in the patients' affected ears. The merits of each of these criteria are discussed and compared with other clinical and operative findings. With the electrocochleographic techniques now employed in searching for acoustic neuromas, false negative results are rare though false positive results are still obtained.