Functional distribution of the extratemporal facial nerve; evoked electromyographic investigation

Abstract

Functional distribution of the extratemporal portion of the facial nerve was investigated in man using intraoperative evoked electromyograghy of the facial muscle. The investigation was performed on the patients who received the parotid tumor surgery of the partial selective neurectomy for the facial spasms. The extratemporal facial nerve was carefully dissected until the fourth branching was identified. An electrical stimulation (the intensity: 2 volts, the duration: 0.1msec) was given first to the facial nerve trunk and then each discrete branch. Using bipolar needle electrodes the evoked EMG was recorded from the frontalis, orbicularis oculi, orbicularis oris and depressor labii inferioris muscles, respectively. The nerve fibers innervating the frontalis muscle existed only in the upper major branch, and the nerve fibers innervating the depressor labii inferioris muscle only in the lower major branch. The orbicularis oris muscle was innervated by both upper and lower branches. The orbicularis oculi muscle was innervated only by the upper branch in six patients, while in other five patients that was innervated by both upper and lower branches. The branches in the parotid gland innervated several facial muscles. These findings gave important bases on the repair of the extratemporal facial nerve in the parotid surgery.