Does electrode placement influence quality of intraoperative monitoring in vestibular schwannoma surgery?

OBJECT: Continuous recording of electromyographic signals (EMG) is a standard method for intraoperative monitoring of facial nerve function in cerebello-pontine angle surgery. Subcutaneous needle electrodes in the facial muscles are used in different setups. The goal of this study was to compare two commonly used electrode setups concering sensitivity for pathological EMG activity. PATIENTS AND METHODS: A group of 10 patients undergoing vestibular schwannoma surgery were examined. Continuous EMG from facial muscles was recorded using needle electrodes in setups according to Kartush or Møller, with narrow or wide interelectrode distances, respectively. Quantity of pathological A-train activity and signal-to-noise ratios were compared between setups.
RESULTS: A-train activity was seen in all patients. On average, 37% of A-train activity was seen in the Kartush setup alone, 4% in Møller setups alone and 59% in both setups synchronously (p<0.05; ratio of median train time--Kartush:Møller 3:2). The wide interelectrode distance of the Møller setup was found to be significantly more susceptible to artefacts, especially to low frequency and power line noise. Artefacts were the main reason for the Møller setup to fail detecting A-train activity.
CONCLUSIONS: For continuous intraoperative monitoring of facial nerve function, narrow interelectrode distance should be used. © Georg Thieme Verlag KG Stuttgart · New York.