DIRECT BRAIN-STEM RECORDING OF AUDITORY-EVOKED POTENTIALS DURING VESTIBULAR SCHWANNOMA RESECTION - NUCLEAR BAEP RECORDING - TECHNICAL NOTE AND PRELIMINARY-RESULTS

The usefulness of intraoperative monitoring in cerebellopontine angle surgery should be improved by obtaining faster and stronger brainstem auditory evoked potential (BAEP) responses. A new technique of direct recording at thee brainstem has been developed, which is applicable to all tumor sizes. By placing a retractor with electrodes attached to i ts tip at the cerebellomedullary junction, the authors have recorded B AEP amplitudes that are 10 times greater than those recorded using the conventional technique. Only small sampling numbers (64-256 recording s) are required and are obtained in 5 to 15 seconds. The technique has been applied successfully in 34 patients who underwent vestibular sch wannoma resections. It has also been tested in patients with intrameat al-extrameatal meningiomas and in those with vascular compressive diso rders; there have been no false results. The advantages of this new te chnique are: 1) identification of BAEP components is easier and faster ; 2) reliable BAEP responses are obtained in some cases in which conve ntional BAEP responses are lost or severely deformed; and 3) BAEP resp onse deterioration and improvement are recognized earlier than would o ccur using the conventional technique. This last advantage provides th e surgeon with a useful warning at a stage of surgery at which BAEP ch anges are still temporary and can be reversed. This method is differen t from other trials of intradural BAEP recordings in three respects: i ts use is not limited to particular tumor sizes; there is no interfere nce with the surgical process; and, most important, the obtained respo nses correlate well with those of conventional BAEP responses, probabl y because the recording site is in the vicinity of the anterior cochle ar nucleus. In conclusion, the chances of useful monitoring feedback w ith adequate adaptation of the microsurgical strategy are improved con siderably.