Intraoperative Monitoring of Facial Nerve Evoked Electromyography: Accurate Identification of the Facial Nerve during Surgery for Cerebellopontine Angle Tumors

The authors have developed an easy, effective method of monitoring intraoperative facial nerve evoked electromyography (IFeEMG) by means of direct electrical stimulation of the intracranial facial nerve. This method was applied in over 32 operations for acoustic neurinomas and other cerebellopontine (CP) angle tumors. With conventional intracranial stimulation the current readily flows through the cerebrospinal fluid and stimulates other cranial nerves, especially the trigeminal nerve, which often leads to false identification of the facial nerve. Because the new method allows both quantitative control of the stimulus and objective recording of the evoked response, it accurately distinguishes the facial muscle response from the responses of other cranial nerve muscles. Thus, IFeEMG facilitates identification and dissection of the facial nerve at the surface of tumors in the CP angle cistern and in the internal auditory canal. This method is superior to conventional techniques for identifying the facial nerve during surgery for CP angle tumors.