gms | German Medical Science

65th Annual Meeting of the German Society of Neurosurgery (DGNC)

German Society of Neurosurgery (DGNC)

11 - 14 May 2014, Dresden

Nervus intermedius influences continuous facial nerve EMG-monitoring

Meeting Abstract

Search Medline for

  • Julian Prell - Klinik für Neurochirurgie, Martin-Luther-Universität Halle-Wittenberg
  • Christian Strauss - Klinik für Neurochirurgie, Martin-Luther-Universität Halle-Wittenberg
  • Stefan Rampp - Klinik für Neurochirurgie, Martin-Luther-Universität Halle-Wittenberg

Deutsche Gesellschaft für Neurochirurgie. 65. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC). Dresden, 11.-14.05.2014. Düsseldorf: German Medical Science GMS Publishing House; 2014. DocMI.15.04

doi: 10.3205/14dgnc354, urn:nbn:de:0183-14dgnc3548

Published: May 13, 2014

© 2014 Prell et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.



Objective: In vestibular schwannoma surgery, facial nerve function may be monitored by quantification of A-trains, a specific pathological pattern, using the parameter traintime. However, false positive results with high traintime and comparatively mild postoperative functional deficits have been observed. This study tries to link this phenomenon to the presence of an anatomically and/or electrophysiologically identifiable Nervus intermedius (NI).

Method: In a consecutive group of 87 patients undergoing vestibular schwannoma surgery, the operative videotapes and electrophysiological data from intermittent electrical stimulation were analysed with respect to the presence/absence of a “split facial nerve”, in which the smaller portion represents the NI. The influence of this dichotomic criterion on facial nerve monitoring results, namely the correlation between traintime and postoperative facial nerve function, was scrutinized.

Results: In the majority of patients (48 out of 87), the NI was identified successfully. In those cases in which it reacted to electrical stimulation, EMG-responses were found mainly in the orbicular oris and the paranasal muscles. Statistical correlation between traintime and functional postoperative outcome was significantly better in the patient group without visible NI as compared to those patients in which the nerve was actually identified (Spearman's Rho 0.73 vs. 0.43). This inferior correlation resulted from additional pronounced A-train activity in EMG-channels covering the orbicular oris and paranasal muscles.

Conclusions: It appears that the NI contributes motor fibers to the facial muscles, targeting mainly the orbicular oris and paranasal muscles. Its presence as an identifiable structure may lead to pronounced manipulation, which in turn seems to interfere with facial nerve monitoring, producing A-train activity without significant clinical correlate.