The simultaneous use of electrocochleogram, brainstem auditory evoked potential and facial muscle EMG in cerebellopontine angle tumor removal.

In six cases of acoustic neurilemmoma, electrocochleogram (ECOchG), brainstem auditory evoked potentials (BAEP) and facial muscle electromyograms (EMG) were recorded to monitor facial nerve and brainstem function. Under isoflurane and nitrous oxide anesthesia, we recorded ECOchG from the tympanic membrane, BAEP from the scalp needle, and facial muscle EMG from the mentalis muscle. During surgery, the body temperature was kept above 36.5 degrees C, and PaCO2 above 30 mmHg. In all cases, the peak N1 of ECOchG and wave I of BAEP had identical latencies throughout the monitoring period. The response was faster and the amplitude was higher in the ECOchG recordings. For calculation of the I-III or I-V interpeak latency of BAEP, the wave I of BAEP could be confirmed more quickly and precisely by the peak N1 of ECOchG. During tumor removal, the embedded facial nerve pathway in the tumor was identified by electric stimulation of the intracranial facial nerve, followed by evoked facial muscle EMG. Facial nerve function was confirmed by nerve traction or direct electric stimulation after total removal of the tumor. No facial palsy or other neurologic sequelae was found after the operations.