Predictive value of intraoperative neurophysiologic monitoring in assessing long-term facial function in grade IV vestibular schwannoma removal.
BACKGROUND
Despite routine use of intraoperative neuromonitoring in acoustic neuroma removal, its application in predicting long-term facial function is limited.


METHODS
Prospective recording of facial nerve function and subsequent review of intraoperative neurophysiologic data. Stimulation of the facial nerve was performed proximal and distal to the tumor locus after tumor removal with measurement of amplitude and latency responses in the orbicularis oculi and oris muscles. Prospective review of current facial nerve function was performed using the House-Brackmann (HB) scoring system. Good facial function was determined as HB I/II and HB III-VI was considered poor facial function. Minimum follow-up time was 15 months, and averaged 40 months.


RESULTS
Twenty-four grade IV acoustic neuromas (54 % larger than 4 cm) were completely removed from October 2008 to November 2013. Nine patients (37.5 %) had HB I/II and 15 (62.5 %) had HB III-VI. The poor prognosis group had a higher latency than the good prognosis group (p = 0.045). Lower proximal amplitude was detected in the poor prognosis group (p = 0.046). Lower proximal-to-distal amplitude ratio was also detected in the poor prognosis group (p = 0.052). Amplitude ratio cut-offs of 0.44 and 0.25 were able to predict poor prognosis with sensitivity of 0.73 and 0.4 and specificity of 0.78 and 1, respectively (p = 0.046).


CONCLUSIONS
Lower proximal amplitude and proximal-distal amplitude ratio were previously reported as predictors of poor facial function in different sizes of vestibular schwannomas. We observed that the same applies specifically for large-sized, completely removed, grade IV tumors. Additionally, we describe a difference in proximal latency time between the good and poor prognosis groups, which was not previously reported.
Faculty of Medicine, University of Porto, Rua Sto António, n°88 São Mateus, Vila Nova Famalicão, 4765-773, Porto, Portugal. sergiodcosta@outlook.com.
Sérgio
S
Duarte-Costa
Faculty of Medicine, University of Porto, Rua Sto António, n°88 São Mateus, Vila Nova Famalicão, 4765-773, Porto, Portugal.|Department of Neurosurgery, Centro Hospitalar São João, Porto, Portugal.|Neurosciences Center, Hospital Cuf Porto, Porto, Portugal.
Rui
R
Vaz
Neurophysiology Unit of the Department of Neurology, Centro Hospitalar São João, Porto, Portugal.
Débora
D
Pinto
Neurophysiology Unit of the Department of Neurology, Centro Hospitalar São João, Porto, Portugal.
Fernando
F
Silveira
Department of Neurosurgery, Centro Hospitalar São João, Porto, Portugal.|Neurosciences Center, Hospital Cuf Porto, Porto, Portugal.
António
A
Cerejo
D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000601:surgery*; D004576:Electromyography / Q000379:methods / Q000592:standards*; D005154:Facial Nerve / Q000502:physiology* / Q000503:physiopathology; D020220:Facial Nerve Injuries / Q000175:diagnosis* / Q000209:etiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring / Q000379:methods / Q000592:standards*; D008297:Male; D008875:Middle Aged; D060787:Neoplasm Grading; D009464:Neuroma, Acoustic / Q000601:surgery*; D019635:Neurosurgical Procedures / Q000009:adverse effects* / Q000379:methods; D011237:Predictive Value of Tests; D011446:Prospective Studies; D016896:Treatment Outcome
Acoustic neuroma; Facial nerve; Proximal amplitude; Proximal latency; Proximal-to-distal amplitude ratio