Establishment of the criteria to evaluate intraoperative changes of brainstem auditory evoked potentials during microvascular decompression and acoustic neurinoma excision

Although monitoring of brainstem auditory evoked potentials (BAEP) is helpful to preserve hearing during operations in the cerebellopontine angle such as microvascular decompression and excision of an acoustic neurinoma, criteria for what and when changes in BAEP should be communicated to the surgeon have nor been well established. An exhaustive review was, therefore, conducted of the English and Japanese literature on this topic. Analysis of the results of this literature review led to the conclusion that during a microvascular decompression procedure, the surgeon should be warned as soon as progressive prolongation of the latency of wave V of the BAEP exceeds 1.5msec. It is reasonable to apply stricter criteria in acoustic neurinoma excision; prolongation of wave V latency even less than 0.5msec should be regarded as the warning sign to the surgeon who is trying to preserve hearing. Whenever BAEP monitoring is performed, it is crucial that changes in the BAEP are evaluated in light of the particular surgical procedure in progress and that the person who evaluates these changes is well versed in the conduct of the surgical procedure.