gms | German Medical Science

68th Annual Meeting of the German Society of Neurosurgery (DGNC)
7th Joint Meeting with the British Neurosurgical Society (SBNS)

German Society of Neurosurgery (DGNC)

14 - 17 May 2017, Magdeburg

Modified motor threshold criterion for intraoperative corticobulbar MEPs for prediction of postoperative facial nerve outcome

Meeting Abstract

  • Tobias Greve - Klinikum der Ludwig-Maximilians-Universität München, Neurosurgical Clinic, Campus Grosshadern, München, Deutschland
  • Liang Wang - Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
  • Jörg-Christian Tonn - Klinikum Grosshadern, Klinikum Grosshadern, Neurochirurgische Klinik und Poliklinik, München, Deutschland
  • Walter Rachinger - University of Munich, Neurochirurgische Klinik und Poliklinik, Dept. of Neurosurgery, München, Deutschland
  • Christian Schichor - Klinikum der Ludwig-Maximilians-Universität München, Neurosurgical Clinic, Campus Grosshadern, München, Deutschland
  • Andrea Szelényi - Klinikum der Ludwig-Maximilians-Universität München, Neurosurgical Clinic, Campus Grosshadern, München, Deutschland

Deutsche Gesellschaft für Neurochirurgie. Society of British Neurological Surgeons. 68. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC), 7. Joint Meeting mit der Society of British Neurological Surgeons (SBNS). Magdeburg, 14.-17.05.2017. Düsseldorf: German Medical Science GMS Publishing House; 2017. DocMO.26.01

doi: 10.3205/17dgnc155, urn:nbn:de:0183-17dgnc1550

Published: June 9, 2017

© 2017 Greve et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at



Objective: Intraoperatively, facial nerve (FN) function is assessed with direct electrical stimulation, observation of spontaneous activity and corticobulbar Motor Evoked Potentials (FN-coMEP). MEP-amplitude decrement and increase in motor threshold (MT) serve as warning criteria. A novel threshold criterion for extremity MEP additionally compared MT-increments to the non-operated side (bilateral final-to-baseline motor threshold level, BFB-MT). We applied BFB-MT for FN-coMEP with regard to postoperative FN-function.

Methods: 47 patients (26f; 46 ± 18yrs., 28 vestibular schwannoma (VS), 12 meningeoma, 2 metastasis, 1 medulloblastoma, 1 lipoma, 1 chordoma, 1 epidermoid cyst, 1 teratoma) undergoing posterior fossa tumor surgery were analysed. FN-function was assessed as per House-Brackmann score (HB) pre- and postoperatively at day 1 (1d), 7 (7d), 3 months (3m) and grouped in mild (HB score increase ≤1) or marked deterioration (HB score increase ≥2). FN-coMEP were elicited with anodal transcranial electric stimulation at C4; C3 referenced to Cz, and recorded from bilateral orbicularis oris and mentalis muscles. A BFB-MT difference of >20% (operated vs. non-operated side) was regarded as significant. Increase of MT on the operated side of ≥20mA served as reference criteriion (RefC). Risk factor analysis for postoperative FN deterioration was performed (patient characteristics, tumor size, extent of resection, BFB-MT and RefC)

Results: At 1d, 15% of the patients (7/47) showed mild HB deterioration, 36% (17/47) marked. At 7d, 12 patients showed mild deterioration (25%), 10 marked (19%). 3m follow-up in 40 patients (85%) showed recovery in 31 patients (78%). 5 patients (13%) showed mild and 4 (10%) marked deterioration (HB 3 (1), HB 4 (2); HB 6 (1)), the latter suffered from giant VS (2), recurrent tumor (1) or NF II (1). FN-coMEP changes according to RefC occurred in 10 patients (39.5±17.2mA) and BFB-MT in 11 patients (35.2±20.6mA), whereas mean threshold increase being 6±7.8mA on the unaffected side. 3/4 patients with FN-coMEP loss showed signs of recovery in their HB score at 3m, but didn’t reach preoperative status. BFB-MT and RefC correlated significantly with FN function at 1d,7d and 3m(p < 0.001). The correlation was stronger using the BFB-MT (spearman correlation: 1d: p = 0.683; 7d: p= 0.741; 3m: p = 0.616) compared to the RefC (spearman correlation: 1d: p = 0.620; 7d: p = 0.564; 3m: p = 0.684). The multivariate analysis revealed BFB-MT to be an independent predictor of postoperative FN deterioration at all 3 time points (1d: p = 0.017; 7d: p < 0.001; 3m: p = 0.002) - despite the low incidence of FN deterioration at 3m.

Conclusion: An increase of BFB-MT of more than >20% between the affected vs. unaffected side serves as a better predictive indicator for postoperative FN function than the RefC. Further, it was identified as an independent variable for postoperative FN-function at 1d, 7d and 3m.