Evolution of Facial Nerve Functional Recovery after Removal of Giant Vestibular Schwannomas

Objectives: To evaluate dynamics of facial nerve (FN) functional restoration after giant vestibular schwannoma (VS) removal, and to investigate possible predictive value of the intraoperative compound action potential (CAP) in FN stimulation.

Methods: In the period from 2009 to 2012, 24 patients with VS were operated on (M:F ratio, 4:20; mean age, 46.9 years). A retrosigmoid approach was used for the total removal of the intracranial and intrameatal portions of the tumor. Average tumor size was 3.2 cm. FN anatomic integrity was restored in all cases (100%). Surgery was performed under the control of intraoperative monitoring of FN and trigeminal nerve. Recording electrodes were inserted into M. orbicularis oculi, M. orbicularis oris, and M. masseter on the ipsilateral side. FN was stimulated by a concentric probe electrode for identification and control of its anatomical integrity. Special attention was drawn to the minimal stimulus intensity for CAP from the proximal portion of FN at the end of the operation. Average minimal intensity power was 3.95 mA (range, 0.2-8 mA). Each patient was carefully evaluated using the House-Brackmann Facial Grading Scale (HB) to assess the severity of paresis of the facial muscles.

Results: Preoperative FN functions: HB I in 8 (33%) patients and HB II-III in 16 (67%); mean HB was 2.08 (±0.58). The next day after the operation, the average results were 4.88 (±1.62); 8 months after the operation, it was 3.75 (±1.65) (t-test, P < 0.05). The first facial movements were observed an average of 4.16 months (range, 1 to 8 months) after surgery. FN function was poor in five patients (21%) 8 months after the operation, so additional procedures such as substitute nerve repair were required. There was a significant correlation (R = 0.78, P < 0.000) between postoperative HB score in 8 months and minimal current intensity needed for facial nerve intraoperative CAP.

Conclusion: Severe FN dysfunction with delayed functional restoration was observed in 70.8% of patients after giant VS removal despite FN anatomical preservation. Additional nerve repair procedures were required in 21% of patients due to poor FN function. The presence of CAP from FN in minimal currency power is an important prognostic sign of functional restoration. The maximum waiting time for restoration of preserved FN function is 8 months.