Correlates of Facial Nerve Outcomes after Acoustic Neuroma Surgery: Results of A Consecutive Series at a Tertiary Care Center

Introduction: Preservation of facial nerve function is an important goal after acoustic neuroma resection. Multiple variables have been studied for their association with satisfactory facial nerve function following the three classic approaches to this tumor. Tumor size, preoperative radiation, experience of the surgical team, intraoperative nerve continuity, and evoked responses have consistently been associated with postoperative facial nerve outcomes. Our goals, in this first phase study, are to substantiate facial nerve outcomes and their correlates after acoustic neuroma surgery.

Methods: This is a retrospective consecutive chart review study, over a seven-year period at a single tertiary care center. A substantial number of patients did not have complete information and were excluded. The study consists of the remaining 192 eligible patients.

Results: All patients were operated on by the same neurosurgeon (JJM), in association with neurotologists. Our population was largely Caucasian (92%), and the majority were female (56%). Mean follow-up was 34 months. Mortality was 0%. More tumors (60%) were resected from the right side. Patients underwent a retrosigmoid (63.5%), translabyrinthine (32.3%) or middle fossa approach (3.7%). One-quarter of the surgeries were performed on tumors proven to have enlarged. Prior treatment was assessed: 10% had prior radiation and 3% prior resection. Gross total (100% volumetric resection) or Near-Total resection (95–99% volumetric resection) was achieved in most (88%) cases. Tumor size was inversely correlated with extent of resection (p < 0.001). Facial nerve function was assessed using the House-Brackmann (HB) scale immediately post-operatively and then at final follow-up. Facial nerve outcomes were stratified as good (HB I-II) or poor (HB III-VI). 39% of patients had some facial weakness immediately postop, yet 49% of them improved to HB I at final follow-up, resulting in a total of 88% of patients having good facial nerve function at last follow-up. The surgical approach was not significantly associated with facial nerve function. A significant correlation was found between the amplitude required to stimulate the facial nerve proximally at end of resection and the final HB grade (p < 0.0001). Interestingly, surgeon’s impression of an abnormal appearing facial nerve intra-operatively was associated with HB score immediately following surgery (p = 0.0006). Hearing outcomes, surgical complications, volumetric resection details and other parameters will be reported at the time of presentation. Recurrence or progression requiring additional treatment was seen in 7% of patients for whom at least 2 years of follow-up data was available. These recurrences occurred in patients with an initial mean volumetric tumor resection of 93%.

Conclusion: Immediate facial nerve weakness after aggressive surgical resection of acoustic neuromas is common, yet the majority of patients will improve, leading to a close to 90% HB I-II at final outcome. Facial nerve outcomes correlate with tumor size, surgical appearance of facial nerve, extent of resection, and intraoperative brainstem exit zone stimulation. These results justify the continued policy of intention for gross total resection, modified by intraoperative judgment based on monitoring and facial nerve appearance.