Intraoperative motor-evoked potential with tetanic stimulation changes pre- and post-hemispherotomy

Abstract

Careful examination of motor evoked potential (MEP) ndings is critical to the safety of intraoperative neuromonitoring during neurosurgery. We reviewed the intraoperative MEP ndings in a pediatric patient who had undergone hemispherotomy for refractory epilepsy. The patient was a four-year-and-two-month-old boy with extensive right cerebral hemisphere, drug-resistant epilepsy, left upper and lower extremity paralysis, and cognitive impairment. We examined intraoperative MEP results both before and after hemispherotomy. Posthemispherotomy, MEPs were successfully elicited through transcranial electrical stimulation (TES) but not via direct cortical stimulation on the right side. Furthermore, TES on the right side, following hemispherotomy, led to a reduction in the MEP ampli cation effect resulting from tetanic stimulation of the left unilateral median and tibial nerves. Conversely, we observed the effects of MEP ampli cation during TES on the left side after tetanic stimulation of these nerves. Postoperatively, the patient underwent magnetic resonance imaging and electroencephalogram examinations, con rming the anatomical and electrophysiological completeness of the dissection. Notably, the seizures disappeared, and no apparent complications were observed. Collectively, our ndings suggest that TES can still activate deep structures and elicit MEPs, even in cases where the corticospinal connections to the posterior limb of the internal capsule are entirely severed. Thalamocortical interactions may affect the MEP ampli cation, observed during tetanic stimulation. Injury to the corticospinal tracts of the white matter may be obscured on conventional MEP ndings; however, it may be identi ed by MEP changes in tetanic stimulation.