gms | German Medical Science

Objective: There is an increasing demand for real-time functional feedback in skull-base surgery involving the oculomotor (CN III) and abducens (CN VI) nerve. Yet until now no standard technology is available to monitor intraoperatively the oculomotor system. The goal of this study was to investigate the feasibility of three modalities (free running electromyogram (EMG), corticobulbar motor evoked potential monitoring (CBT MEP) and direct nerve stimulation (DNS)) and to correlate intraoperative signal changes to postoperative outcome.

Method: A surgical series of sphenoid wing meningioma with involvement of CN III and CN VI was included from 2013-2015. EMG recording was performed via needle electrodes placed in the lateral (CN VI) and inferior (CN III) rectus muscle. CBT MEP were elicited by transcranial electrical stimulation with a train of 4-5 stimuli, 0.5-0.8 msec pulse duration and 2-4 msec ISI. DNS was performed with a bipolar concentric probe at 3 Hz with a 0.01 mA to 1 mA stimulation intensity. Intraoperative changes were correlated to postoperative outcome of CN III and CN VI nerve function.

Results: The above mentioned protocol was performed in 20 cases. One patient (5%) presented a postoperative CN VI palsy. EMG of the CN III and CN VI was successfully recorded in all cases. One patient presented intraoperative long persisting EMG train activity and CBT MEP loss of CN VI; this patient had a postoperative CN VI palsy. Another patient presented a progressive CBT MEP motor threshold increment of CN III and CN VI but both nerves could still be activated by DNS; this patient had no postoperative deficit. In one patient no CBT MEP of CN VI could be recorded since baseline. The remaining 17 patients had stable CBT MEP (n = 11) or unspecific (n = 6) changes, all patients presented no postoperative deficit.

Conclusions: We could demonstrate that intraoperative monitoring of CN III and CN VI is a feasible and reliable tool to predict postoperative outcome.