gms | German Medical Science

Objective: In vestibular schwannoma (VS) surgery postoperative facial nerve (CNVII) palsy is an important stigma reducing quality of life significantly. Different intraoperative neurophysiological monitoring methods have been described: observing free-running EMG for train types or monitoring motor evoked potentials for functional integrity. However none of those are able to localize the CNVII which might be hidden in large tumors. Mapping provides that information yet is an intermittent method where the surgeon has to stop surgery to take the stimulation probe. Recently we have introduced a continuous mapping method in supratentorial surgery. The objective of this study was to adapt that method to VS surgery.

Methods: Additionally to standard neurophysiological techniques, continuous mapping was performed in a series of large VS (01/2015 to 04/2017). A surgical suction aspirator was modified to be used simultaneously for surgical dissection and continuous monopolar stimulation (Figure 1 [Fig. 1]). Stimulation was performed with intensity from 1.5 mA - 0.05 mA depending on the surgical step; 0.3msec cathodal pulse duration and 2.0Hz rate. Recordings were done from orbicularis oculi, levator labialis, orbicularis oris and mentalis muscle. Postoperative CN VII outcome was assessed by the House-Brackmann-Score (HBS) one day, one week and 3 months after surgery.

Results: The method was performed in 21 patients with Koos III (n=6; 29%) and Koos VI (n=15; 71%) VS. Preoperative HBS was 1 in 19 and 2 in 2 patients. Direct after surgery 7 and one week later 6 patients presented worsening in HBS. At 3 months follow-up 3 patients (14%) still had an impairment of CN VII (HBS 3; 3 and 4).

Conclusion: The continuous dynamic mapping method using an electrified surgical suction device might be a valuable additional tool in surgery of large VS. It might provide a real-time feed-back of the remaining distance and course of the CN VII.