[Intra- and perioperative acoustic evoked brain stem potentials in cerebellopontile angle operations]

From a series of 35 cases with intraoperative monitoring of acoustic evoked brainstem responses 4 cases with cerebellopontine angle surgery are presented in detail. The aim of neuromonitoring is to provide the surgeon with an additional instrument to assess the functional state of the hearing pathway with objective neurophysiological criteria during dissection near the eighth nerve and brainstem. Thus, a near total loss of potential during a neurovascular decompression of the trigeminal nerve could be reversed by modifying the surgical procedure. In 2 cases of acoustic neurinoma with preserved wave I this peak was obtainable throughout the procedure with a good postoperative result. Transient amplitude attenuation and latency increase was seen with a meningioma, which normalized before the end of operation with good postoperative hearing and brain-stem function. The relationship between intraoperative BAEP changes and postoperative brain-stem and eighth nerve function, and the value of neuromonitoring are discussed with regard to surgery around the internal auditory meatus and the eighth nerve.