Monitoring Auditory Evoked Potentials During Cerebellopontine Angle Tumor Surgery: Relative Value of Electrocochleography, Brainstem Auditory Evoked Potentials, and Cerebellopontine Angle Recordings

Abstract

Recording short-latency auditory evoked potentials continuously throughout cerebellopontine angle (CPA) tumor surgery with electrocochleography (ECochG) and brainstem auditory evoked potentials (BAEP) monitors the status of the cochlea, auditory nerve peripheral to the tumor, and neural activity central to the tumor. ECochG is a nearfield potential and provides rapid feedback, whereas BAEP are farfield potentials and their feedback is slower. Whenever the later components (wave V) of the BAEP are detectable, an electrode positioned within the CPA can usually record a negative potential due to neural activity central to the tumor. This recording technique will often detect a positive component from the generator of N1, but no cochlear potentials. The nearfield negative potential can provide much more rapid feedback than wave V, but it has the same predictive value for hearing as wave V: when present it predicts useful hearing, but when undetectable hearing outcome cannot be predicted. By contrast, when neural activity is present in the ECochG, hearing outcome cannot be predicted, but when it is undetectable, hearing is always lost. There is a fundamental limitation of electrophysiological monitoring: when neural activity can be detected peripheral to the tumor but not central to the tumor, the electrophysiological data cannot predict postoperative hearing.