Intraoperative neurophysiological monitoring to protect the facial nerve during microsurgery for large vestibular schwannomas.

OBJECTIVE: Microsurgery is the preferred treatment for large vestibular schwannomas (VSs). However, anatomical and functional preservation of the facial nerve (FN) remains a challenge during this surgery. The aim of this study was to determine whether it is beneficial to the preservation rates of the FN during microsurgical treatment of large VSs using intraoperative neurophysiological monitoring (IONM).

METHODS: We retrospectively reviewed 53 patients with large VSs that underwent microsurgical resection via the retrosigmoid approach in our department during April 2009 to March 2016. IONM was used in 29 cases. Postoperative FN function was evaluated using the House-Brankmann (HB) FN grading scale at 2 weeks and 3 and 6 months after surgery.

RESULTS: There were two cases (8.3%) of subtotal resection in the monitored group, compared with one case (3.4%) among the controls (p>0.05). The anatomical integrity rate for FNs was 100% in the monitored group, which was significantly different from 83.3% in the controls (p<0.05), which included four cases the FN was injured, mostly around the internal auditory foramen. Functional preservation of the FN in the monitored group differed significantly from that in the controls at 2 weeks and 3 and 6 months postoperatively (p<0.05).

CONCLUSIONS: IONM contributes to FN anatomical integrity and functional preservation rates during microsurgery of large VSs. It has no significant effect on differences in the total VS resection rates.