title: The intermedius nerve as a confounding variable for monitoring of the free-running electromyogram.
abstract: OBJECTIVE
  A-trains, a facial nerve EMG-pattern, are correlated with postoperative functional impairment. However, an unknown confounder is suspected to cause false positive monitoring results. The intermedius nerve contains motor fibers targeting lower facial muscles; their significance for facial nerve monitoring is yet unknown.
  
  
  METHODS
  Intraoperative videotapes and free-running 9-channel facial nerve EMG assessed from 87 patients undergoing surgery for vestibular schwannoma were evaluated, and presence/absence of an identifiable intermedius nerve was determined. The prognostic value of train time, a quantitative measure for A-train activity, was evaluated for both the groups with and without an identifiable intermedius nerve.
  
  
  RESULTS
  Correlation between traintime and outcome (Spearman's Rho) rose to 0.73 (p<0.001) when only patients without an identified intermedius nerve were considered, and fell to 0.43 (p<0.05) with the other patient group. This difference was statistically significant (p=0.036), was more prominent in the channels monitoring perioral facial muscles, and resulted from additional A-train activity in patients with an identifiable intermedius nerve.
  
  
  CONCLUSIONS
  A separate intermedius nerve may be more prone to manipulation, leading to A-train activity without clinical correlate, thus causing false positive monitoring results.
  
  
  CONCLUSIONS
  For interpretation of the free-running EMG, the intermedius nerve needs to be taken into account as a confounder.
authors: Department of Neurosurgery, University of Halle, Ernst-Grube-Str. 40, 06097 Halle, Germany. Electronic address: julian.prell@medizin.uni-halle.de.
authors: Julian
authors: J
authors: Prell
authors: Department of Neurosurgery, University of Halle, Ernst-Grube-Str. 40, 06097 Halle, Germany.
authors: Christian
authors: C
authors: Strauss
authors: Department of Neurosurgery, University of Halle, Ernst-Grube-Str. 40, 06097 Halle, Germany.
authors: Jens
authors: J
authors: Rachinger
authors: Department of Neurosurgery, University of Halle, Ernst-Grube-Str. 40, 06097 Halle, Germany.
authors: Christian
authors: C
authors: Scheller
authors: Department of Neurosurgery, University of Halle, Ernst-Grube-Str. 40, 06097 Halle, Germany.
authors: Alex
authors: A
authors: Alfieri
authors: Department of Neurosurgery, University of Halle, Ernst-Grube-Str. 40, 06097 Halle, Germany.
authors: Kirsten
authors: K
authors: Herfurth
authors: Department of Neurosurgery, University of Halle, Ernst-Grube-Str. 40, 06097 Halle, Germany.
authors: Stefan
authors: S
authors: Rampp
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D004576:Electromyography / Q000379:methods*; D005154:Facial Nerve / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009464:Neuroma, Acoustic / Q000175:diagnosis* / Q000503:physiopathology* / Q000601:surgery; D055815:Young Adult
keywords: A-train; EMG; Neurophysiologic monitoring; Split facial nerve; Traintime; Vestibular schwannoma