Facial nerve motor-evoked potential monitoring during skull base surgery predicts facial nerve outcome

Abstract

Intraoperative FNMEP monitoring can be useful for predicting facial nerve function after skull base surgery. This new method is a valuable adjunct to conventional facial nerve monitoring.

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

“…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. 2,4,7,8 With the warning criterion at 20 mA, an intraoperative warning was associated with a risk of PPV of 83% (CI 59%-96%) of postoperative deterioration of facial nerve function. A high NPV of 88% (CI 62%-98%) indicates that the absence of an intraoperative warning predicts good postoperative facial nerve function.…”

“…13 More recently, the indication for MEP monitoring has been extended to also monitor the function of the corticobulbar tract, and, in particular, facial nerve function. 4,7 Most authors consider a reduction in FNMEP response amplitude of more than 50% as a warning criterion [1][2][3][4]7,8,12 as widely accepted for MEPs in supratentorial surgery. 15,19 The threshold-level method was first proposed for monitoring spinal cord function.…”

“…Most authors use the decrease in FNMEP response amplitude as a warning criterion. [1][2][3][4]8,12 However, FNMEP responses have inherent variability and are hard to quantify. Also, high FNMEP stimulation intensity is needed to achieve maximal FNMEP response already at baseline so that subsequent response deterioration can be assessed.…”

Intraoperative Transcranial Motor-Evoked Potential Monitoring of the Facial Nerve during Cerebellopontine Angle Tumor Resection

“…Although optimal stimulation parameters for TCMEP of the FN remain unknown, current data support previously published techniques using multipulse stimulation of 3 to 5 trains, duration 0.2 to 0.5 milliseconds, and interstimulus interval of 4 milliseconds. [20][21][22]24 These parameters successfully minimized peripheral FN activation yet were able to overcome anesthesia-induced suppression of MEP. In addition to stimulation parameters, many factors are known to affect TCMEP monitoring, including anesthesia, use of muscle relaxants, number and type of recording electrodes, and individual patient variation.…”

“…[20][21][22][23][24][25][26] Studies indicate that TCMEP of the facial nerve is feasible and may predict immediate postoperative outcome. Long-term functional data and the relationship between TCMEP and facial nerve function beyond the immediate postoperative period is lacking.…”