CONTINUOUS RETROGRADE MONITORING OF THE FACIAL-NERVE - PRELIMINARY EXPERIENCE DURING ACOUSTIC NEUROMA SURGERY

Continous electromyographical (EMG) monitoring of the facial nerve is widely used during acoustic tumor surgery. Mechanical stimulation of t he facial nerve is capable of eliciting synchronous and asynchronous E MG responses alerting the surgeon to damaging maneuvers performed on t he nerve. Mechanical stimulation, however, elicits EMG responses only when the nerve has been injured by the underlying pathology or previou s surgical maneuvers, and the technique is sensitive to administration of muscular blockers. In addition, EMG is unable to furnish quantitat ive information about the damage. The present paper illustrates an alt ernative technique for intraoperative facial nerve monitoring, that is , the recording of facial nerve antidromic potentials (FNAPs). Eleven subjects operated on by acoustic neuroma surgery via a retrosigmoid ap proach (tumor sizes ranging from 12 to 28 mm) participated in the inve stigation. Bipolar electrical stimulation of the marginalis mandibulae was performed to elicit FNAPs. Stimulus intensity ranged from 2 to 6 mA with a delivery rate of 7/second. A silver-wire electrode positione d on the proximal portion of the acoustic-facial bundle was used to re cord action potentials. Changes in latency and amplitude of FNAPs were analyzed as a function of the main surgical steps. FNAP monitoring pr ovided quantitative real-time information about damaging maneuvers per formed on the nerve and allowed prediction of postoperative facial fun ction.