Skull Base 2011; 21 - A073
DOI: 10.1055/s-2011-1274248

Intraoperative Transcranial Motor-Evoked Potential Monitoring of the Facial Nerve during Cerebellopontine Angle Tumor Resection

Maura Cosetti 1(presenter), Ming Xu 1, Andrew Rivera 1, Maggie Kuhn 1, John G. Golfinos 1, J. Thomas Roland 1
  • 1New York, USA

Background: Intraoperative monitoring of the facial nerve (FN) by continuous electromyography (EMG) and direct stimulation is routine and has been shown to improve FN outcome during cranial base surgery. However, direct stimulation requires identification of the FN and implies functional integrity only between the site of stimulation and the recording electrodes. In contrast, motor-evoked potential (MEP) monitoring of the FN using transcranial stimulation of the motor cortex does not require direct nerve stimulation and yields information regarding the full facial nerve pathway. This novel method has shown initial utility in surgery of skull base tumors involving the facial nerve.

Objective: The purpose of this study was to determine whether intraoperative transcranial MEP monitoring of the FN during cerebellopontine angle (CPA) tumor resection can predict both immediate and long-term postoperative FN function.

Methods: Intraoperative transcranial facial MEPs were obtained using corkscrew scalp electrodes placed at C3, C4, and Cz with paired recording needle electrodes placed in the orbicularis oris. Multipulse stimulation was employed with an interstimulus interval of 0.4 milliseconds, duration of 0.2–0.5 milliseconds, rate of 1.0 Hz, train rate of 250–45 Hz, train count of 3, and stimulation of 100–250 V. Baseline, final, and ratio of final-to-baseline facial nerve MEP, as well as preoperative, immediate, and long-term postoperative facial nerve function using House-Brackmann (HB) grade, were recorded and analyzed.

Results: Intraoperative FN MEP data and immediate and long-term facial nerve outcome were available for 55 patients undergoing CPA tumor resection. The ratio of final-to-baseline facial nerve MEP correlated significantly (P < 0.05) with both immediate and long-term facial nerve outcome.

Conclusion: Intraoperative transcranial MEP of the facial nerve can be a valuable adjunct to conventional facial nerve EMG during resection of tumors at the CPA. Final-to-baseline MEP ratio can predict both immediate and long-term facial nerve outcome.