gms | German Medical Science

Objective: To determine whether transcranial motor-evoked potential monitoring of the facial nerve (FNMEP) during eloquent tumor resection is feasible in children and can predict both immediate and postoperative FN or pyramidal tract function.

Method: We included 24 consecutive procedures involving 21 patients (median age 5.5 y, range 5 mo - 15 y, 8 female) that were operated on with FNMEP monitoring in 2013 and 2014. During surgery, we maintained a constant response amplitude by increasing the stimulation intensity and aimed to establish a warning criterion based on the "threshold-level" method. A threshold increase of greater than 20 mA for eliciting the FNMEP in the most reliable facial nerve target muscle was considered to be a prediction of reduced postoperative facial nerve function and consequently, a warning was given to the surgeon. The preoperative and early postoperative function was documented using the House-Brackmann (HB) grading system and general motors outcome for the extremities.

Results: Monitoring of the FNMEP was feasible in all the surgeries in at least one facial nerve target muscle. The orbicularis oris muscle yielded the best result (95% of the trials), followed by the mentalis (87%) and orbicularis oculi muscles (86%). The median stimulation threshold was initially 65 mA (range 40-110 mA) for the FNMEP and 60 mA (15-220 mA) for the MEP of the thenar muscles. The FNMEP deterioration showed a sensitivity of 100% for HB deterioration and specificity of 74%. More experience with FNMEP led to increase in resection rate through continues stable neuromonitoring especially after longer surgeries compared to standard MEP.

Conclusions: FNMEP monitoring provides valid evidence for FN function in eloquent and pediatric skull base surgery and seems more reliable for general motor outcome compared to standard MEP measurements in longer pediatric surgeries.