Clinical Usefulness of Intraoperative Motor-Evoked Potential Monitoring during Temporal Lobe Epilepsy Surgery

Abstract

Background and purpose: We aimed to determine the effectiveness of intraoperative neurophysiological monitoring focused on the transcranial motor-evoked potential (MEP) in patients with medically refractory temporal lobe epilepsy (TLE).

Methods: We compared postoperative neurological deficits in patients who underwent TLE surgery with or without transcranial MEPs combined with somatosensory evoked potential (SSEP) monitoring between January 1995 and June 2018. Transcranial motor stimulation was performed using subdermal electrodes, and MEP responses were recorded in the four extremity muscles. A decrease of more than 50% in the MEP or the SSEP amplitudes compared with baseline was used as a warning criterion.

Results: In the TLE surgery group without MEP monitoring, postoperative permanent motor deficits newly developed in 7 of 613 patients. In contrast, no permanent motor deficit occurred in 279 patients who received transcranial MEP and SSEP monitoring. Ten patients who exhibited decreases of more than 50% in the MEP amplitude recovered completely, although two cases showed transient motor deficits that recovered within 3 months postoperatively.

Conclusions: Intraoperative transcranial MEP monitoring during TLE surgery allowed the prompt detection and appropriate correction of injuries to the motor nervous system or ischemic stroke. Intraoperative transcranial MEP monitoring is a reliable modality for minimizing motor deficits in TLE surgery.

Keywords: intraoperative monitoring; motor-evoked potentials; temporal lobe epilepsy.

Fig. 1. MEP changes during epilepsy surgery in case 8. A: The early waves of MEP and SSEP before craniectomy are shown. Left and right MEP are in upper panel. Left median, right median, left posterior tibial, and right posterior tibial nerve SSEP (from left to right) are in lower panel. Waves in green are real-time acquired data, while those in black are baseline one. B: In MEP monitoring, the waves in right lower extremity disappeared for 17 minutes during temporal lobe epilepsy surgery (arrowhead). No significant changes in SSEP occur throughout the operation. The photo shows the operative field in right ATL+AH. ADQ: abductor digiti quinti, AH: abductor halluces, APB: abductor pollicis brevis, ATL: anterior temporal lobectomy, LT: left, MEP: motor-evoked potential, RT: right, SSEP: somatosensory evoked potential, TA: tibialis anterior.

Fig. 2. Stack images of MEP changes during epilepsy surgery in case 8. A: In left MEP monitoring, no significant wave changes of right upper and lower extremities are observed during the surgery. B: In right MEP monitoring, MEP disappears for 17 minutes (open arrow) and recovers after releasing cerebral retraction (closed arrow). ADQ: abductor digiti quinti, AH: abductor halluces, APB: abductor pollicis brevis, Lt: left, MEP: motor-evoked potential, Rt: right, TA: tibialis anterior.