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Continuous dynamic mapping to avoid accidental injury of the facial nerve during surgery of large vestibular schwannomas
Author(s): ,
K. Seidel
Affiliations:
Inselspital, Bern University Hospital, Department of Neurosurgery, Bern, Switzerland
,
M. Biner
Affiliations:
University of Bern, Bern, Switzerland
,
I. Zubak
Affiliations:
Inselspital, Bern University Hospital, Department of Neurosurgery, Bern, Switzerland
,
J. Rychen
Affiliations:
Inselspital, Bern University Hospital, Department of Neurosurgery, Bern, Switzerland
,
J. Beck
Affiliations:
Inselspital, Bern University Hospital, Department of Neurosurgery, Bern, Switzerland
A. Raabe
Affiliations:
Inselspital, Bern University Hospital, Department of Neurosurgery, Bern, Switzerland
EANS Academy. Seidel K. Oct 21, 2018; 225726; EP4121
Assoc. Prof. Kathleen Seidel
Assoc. Prof. Kathleen Seidel
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Abstract
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Objective
In vestibular schwannoma (VS) surgery postoperative facial nerve (CN VII) palsy is an important stigmatism. Electromyography and intermittent mapping with a separate stimulation probe is used to localize CN VII during surgery. The objective of this study was to adapt the technique of continuous dynamic mapping to surgery of large VS and to investigate whether this method is reliable to warn the surgeon about close vicinity of the hidden nerve fibers .

Methods
Continuous dynamic mapping was performed additionally to standard neurophysiological monitoring techniques using a combined suction and stimulation probe as described earlier. Monopolar stimulation was performed with intensities from 0.25 - 2 mA (0.3 msec cathodal pulse duration, 2.0 Hz rate). Recordings were done from orbicularis oculi, levator labialis, orbicularis oris and mentalis muscle. Postoperative CNVII outcome was assessed using House-Brackmann-Score (HBS) 3 months after surgery.

Results
Continuous dynamic mapping was applied in 20 patients with 18 Koos VI (90%) and 2 Koos III (10%) vestibular schwannomas. Preoperative HBS was 1 in 19 and 2 in 1 patient. Mean tumor volume was 16.4 cm3; mean resection rate was 92%. Mapping reliably indicated presence of CN VII within 2-10 mm depending on the stimulation intensity. At 3 months follow-up 17 patients had intact CV II function (HBS 1) and 3 patients (15%) moderate impairment (HBS 3 and 4). Despite a general strategy of planned near total resection, facial nerve deficit rate was zero only in the subgroup of patients where any attempt to separate the adherent nerve from the capsule was avoided.

Conclusion
The continuous dynamic mapping method using an electrified surgical suction device reliably indicates the presence of the facial nerve within 2-10 mm depending on the stimulation intensity and helps to avoid accidental injury to the nerve.
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