Transcranial electrocortical stimulation to monitor the facial nerve motor function during cerebellopontine angle surgery.
OBJECTIVE
This study was conducted to investigate the success rate of using the facial motor evoked potential (FMEP) of orbicularis oculi and oris muscles for facial nerve function monitoring with use of a stepwise protocol, and its usefulness in predicting facial nerve outcome during cerebellopontine angle (CPA) surgeries.


METHODS
FMEPs were recorded intraoperatively from 60 patients undergoing CPA surgeries. Transcranial electrocortical stimulation (TES) was performed using corkscrew electrodes positioned at hemispheric montage (C3/C4 and CZ). The contralateral abductor pollicis brevis muscle was used as the control response. Stimulation was always applied contralaterally to the affected side using 1, 3, or 5 rectangular pulses ranging from 200 to 600 V with 50 micros of pulse duration and an interstimulus interval of 2 ms. Facial potentials were recorded from needles placed in the orbicularis oculi and oris muscles.


RESULTS
FMEP from the orbicularis oris and oculi muscles could be reliably monitored in 86.7% and 85% of the patients, respectively. The immediate postoperative facial function correlated significantly with the FMEP ratio in the orbicularis oculi muscle at 80% amplitude ratio (P = .037) and orbicularis oris muscle at 35% ratio (P = .000). FMEP loss was always related to postoperative facial paresis, although in different degrees.


CONCLUSIONS
FMEPs can be obtained reliably by using TES with 3 to 5 train pulses. Stable intraoperative FMEPs can predict a good postoperative outcome of facial function. However, further refinements of this technique are necessary to minimize artifacts and to make this method more reliable.
Department of Neurosurgery, University of Tübingen, Tübingen, Germany, and Department of Neurology, University of São Paulo, São Paulo, Brazil.
Marcus André
MA
Acioly
Marina
M
Liebsch
Carlos Henrique
CH
Carvalho
Alireza
A
Gharabaghi
Marcos
M
Tatagiba
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003390:Cranial Nerve Neoplasms / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D004558:Electric Stimulation / Q000379:methods*; D005154:Facial Nerve / Q000502:physiology / Q000601:surgery*; D020220:Facial Nerve Injuries / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation / Q000379:methods*; D009464:Neuroma, Acoustic / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D055815:Young Adult