gms | German Medical Science

64th Annual Meeting of the German Society of Neurosurgery (DGNC)

German Society of Neurosurgery (DGNC)

26 - 29 May 2013, Düsseldorf

Facial nerve motor-evoked potentials during skull base surgery to monitor facial nerve function by the “threshold-level” method

Meeting Abstract

  • Johannes Sarnthein - Klinik für Neurochirurgie, UniversitätsSpital Zürich, Switzerland; Center for Integrative Human Physiology, Universität Zürich, Switzerland
  • Nader Hejrati - Klinik für Neurochirurgie, UniversitätsSpital Zürich, Switzerland
  • Marian Christoph Neidert - Klinik für Neurochirurgie, UniversitätsSpital Zürich, Switzerland
  • Alexander Huber - Klinik für Ohren-, Nasen-, Hals- und Gesichtschirurgie, UniversitätsSpital Zürich
  • Niklaus Krayenbühl - Klinik für Neurochirurgie, UniversitätsSpital Zürich, Switzerland

Deutsche Gesellschaft für Neurochirurgie. 64. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC). Düsseldorf, 26.-29.05.2013. Düsseldorf: German Medical Science GMS Publishing House; 2013. DocMI.10.06

doi: 10.3205/13dgnc362, urn:nbn:de:0183-13dgnc3629

Published: May 21, 2013

© 2013 Sarnthein 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: During surgeries that put the facial nerve (FN) at risk of injury, FN function can be continuously monitored by transcranial FN motor evoked potentials (FNMEPs) in FN target muscles. Despite their advantages, FNMEPs are not yet widely used. While most authors use a 50% reduction of FNMEP response amplitudes as a warning criterion, our approach was to keep the response amplitude constant by increasing the stimulation intensity and to establish a warning criterion based on the “threshold-level” method.

Method: We included 31 consecutive adult patients (median age 46 years) where FNMEPs were monitored. A threshold increase >20mA for eliciting FNMEPs in the most reliable FN target muscle was considered a prediction of reduced postoperative FN function and subsequently a warning was issued to the surgeon. Pre-and early postoperative function was documented using the House-Brackmann (HB) grading system.

Results: FNMEP monitoring was feasible in all 31 surgeries in at least one FN target muscle. The mentalis muscle yielded best results. HB grade deteriorated in 14/31 patients (45%). The warning criterion was reached in 16/31 patients (52%), which predicted an 81% risk of HB deterioration. Sensitivity amounted to 93% (CI 66%-100%) and specificity to 82% (CI 57%–96%). FNMEP deterioration and deteriorated HB grade showed a high degree of association (p<0.001). The impact of FNMEP monitoring on surgical strategy is exemplified in one illustrative case.

Conclusions: In surgeries that put the facial nerve at risk, the intraoperative increase in FNMEP stimulation threshold was closely correlated to postoperative facial nerve dysfunction. FNMEP monitoring is a valid indicator of FN function in skull base surgery. It should be used as an adjunct to direct electrical FN stimulation and continuous EMG monitoring of FN target muscles.