Auditory brain stem responses in patients with acoustic neuromas.

In the continuing search for methods to diagnose acoustic neuromas at an early stage, we have applied the auditory brain stem response examination to 27 patients with surgically verified acoustic neuromas. It is confirmed that the main indicator of retrocochlear versus cochlear disease is the interaural latency difference of the Jewett5 wave, the IT5. Women exhibit significantly lower latency values to J5 than men, approximately 0.25 msec. Age also has some influence, so that the J5 latency tends to increase with age, but in this investigation the trend did not reach statistical significance. We were unable to find a correlation between tumour size and IT5. Even if the audiogram shows a considerable hearing impairment at 2 kHz this technique can be used without any correction factors, when the stimulus is a 2 kHz filtered tone-pip. In the presence of an acoustic neuroma there will often be adaptation of the response and it is preferable to arrange the mode of stimulus presentation so that this phenomenon eventually becomes prominent. One patient came out with a false-negative result. We believe this to have been due to our lack of experience at that time and that today we would have recognized the presence of a tumour. If this correction is accepted, the series contains no false-negatives. Regardless of this it can be concluded that for the time being, out of the functional audiological tests, the auditory brain stem response examination is the most reliable indicator for the presence of retrocochlear lesions.