• Stefan Rampp, Jörg Illert, Katja Krempler, Christian Strauss, and Julian Prell.
• Department of Neurosurgery, University Hospital Halle (Saale), Ernst-Grube-Str. 40, 06120 Halle (Saale), Germany. Electronic address: Stefan.rampp@uk-halle.de.
• Clin Neurophysiol. 2019 May 1; 130 (5): 722-726.

ObjectiveEMG "A-train" activity correlates with postoperative facial palsy after vestibular schwannoma (VS) surgery. An intermedius nerve separate from the facial nerve increases A-trains without significant impact on function. We investigate occurrence of A-train "clusters", A-trains over a majority of channels within a short time frame.MethodsData from 217 patients with first surgery for VS were evaluated retrospectively. Continuous EMG recorded with 9 channels was evaluated for A-train patterns. "Clusters" of A-trains were identified, i.e. A-trains within 3 seconds over a majority of channels. Relation to a separate intermedius, tumor size and facial palsy was evaluated.ResultsCorrelations between A-trains and postoperative facial palsy were higher in patients without separate intermedius (r = 0.562 versus r = 0.194). Clusters were identified in 107 patients (49.3%), separate intermedius in 109 (50.2%), with significant association of both (p < 0.001, Chi-Square test). Excluding clusters slightly increased correlation of A-trains to facial nerve function.ConclusionsA-train clusters have limited relevance for predicting postoperative paresis. However, they should be regarded as warning signs, suggesting the presence of a separate intermedius nerve.SignificanceA-train "clusters" are a sign of hyperactivity of the facial nerve due to a separate intermedius nerve and may confound intraoperative monitoring during VS surgery.Copyright © 2019 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

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