Intraoperative Monitoring of Motor Evoked Potential for the Facial Nerve Using a Cranial Peg-Screw Electrode and a “Threshold-level” Stimulation Method

Abstract

Transcranial motor evoked potential (MEP) for the facial nerve (facial MEP) has been recognized as a good method for quantitative monitoring of facial nerve function in skull base surgery. To improve the feasibility and safety of facial MEP monitoring, a peg-screw electrode and a "threshold-level" method were investigated. From 2007 to 2009, intraoperative facial MEP monitoring with the peg-screw electrode and threshold-level method was successfully achieved in 26 of 29 patients who underwent surgery for the posterior fossa extra-axial tumor. The relationship between the change in the facial MEP threshold level and the postoperative function of the facial nerve was analyzed in 23 patients who had no facial palsy preoperatively. There were no complications associated with facial MEP monitoring. Nine patients who had stable facial MEP threshold had no facial palsy. Fourteen patients who had worsened but measurable facial MEP threshold had mild palsy at discharge. Two of three patients who had severely worsened and unmeasurable facial MEP threshold had severe facial palsy. The change in the facial MEP was well correlated with the postoperative facial function. The peg-screw electrode and threshold-level method are good options for facial MEP monitoring.

Facial nerve motor evoked potentials during skull base surgery to monitor facial nerve function using the threshold-level method

“…5 There is one report of FNMEP threshold monitoring in the literature. 9 We report here a series of surgeries in which FNMEPs were analyzed by the threshold-level method to monitor facial nerve function intraoperatively. With this approach we obtained a sensitivity of 88% and a specificity of 82%, which is in the range of values reported by other authors.…”

“…Several criteria have been proposed to distinguish between corticobulbar and peripheral stimulation. [2][3][4][7][8][9]12 Ideally, a corticobulbar FNMEP response should oc cur after a latency of about 10 msec and it should be polyphasic. Furthermore, it has been claimed that a corticobulbar response requires stimulation by a train of several pulses, and response to a single pulse is due to peripheral stimulation.…”

“…Also, high FNMEP stimulation intensity is needed to achieve maximal FNMEP response already at baseline so that subsequent response deterioration can be assessed. Inspired by promising findings in IONM of motor function during surgery at the level of the spine, 5 the cortex, 17 the brainstem, 16 and the facial nerve, 9 we propose here to monitor the increase in stimulation threshold needed to elicit FNMEPs to communicate with the surgeon and to predict postoperative facial nerve function.…”

Potencial evocado motor facial durante cirurgias para tumores da base de crânio e do ângulo ponto-cerebelar

“…Acioly MA, Telles C, Aguiar PHP, Tatagiba M -Potencial evocado motor facial durante cirurgias para tumores da base de crânio e do ângulo ponto-cerebelar: uma revisão sistemática dos critérios eletrofisiológicos de prognóstico da função facial resultados e dIscussão A busca eletrônica do banco de dados PubMed detectou 82 estudos, dos quais apenas 9 artigos, a envolver 436 pacientes, foram passíveis de inclusão. 1,3,4,8,9,11,13,25,41 Todos os estudos foram nível III de evidência. A tabela 1 promove uma discussão detalhada dos estudos publicados sobre os critérios eletrofisiológicos de prognóstico da função facial baseados nos resultados do PEMF, a incluir os seguintes aspectos: o desenho do estudo, o número de pacientes, a histologia dos tumores, o protocolo de estimulação, o número de canais de monitorização, os critérios eletrofisiológicos de interpretação, assim como os resultados obtidos.…”

Comparison of effectiveness between cork-screw and peg-screw electrodes for transcranial motor evoked potential monitoring using the finite element method

“…Some authors reported that peg-screw electrodes screwed into the skull can more effectively conduct current to the brain compared to subdermal cork-screw electrodes screwed into the skin. [114] The stimulus currents from the peg-screw pass more effectively through the high-resistance skull. Furthermore, direct cortical electrodes produce higher electric fields than transcranial electrodes of either type.…”