Direct Cortical Motor Evoked Potentials Versus Transcranial Motor Evoked Potentials for the Detection of Cortical Ischemia During Supratentorial Craniotomy: Case Report

Transcranial motor evoked potential (TCMEP) and direct cortical motor evoked potential (DCMEP) paradigms have historically been used contemporaneously or independently for supratentorial craniotomies. DCMEP provides focal stimulation to the cortical surface, whereas TCMEP stimulation is more variable and may be activating structures deeper than those at risk during a supratentorial craniotomy. We present the case report for a 65-year-old female who underwent a supratentorial craniotomy for the clipping of a right-sided unruptured middle cerebral artery (MCA) aneurysm. DCMEP recordings of the upper extremity degraded after the parent vessel was temporarily occluded with a clip. The recordings returned once the clip was released. The DCMEP lower extremity recordings did not deviate from their established baseline. TCMEP recordings (upper and lower extremities) also did not deviate from their established baselines. The permanent clip was placed without incident, and the patient awoke neurologically intact. This case study demonstrates the specificity and sensitivity of DCMEP vs. TCMEP. DCMEP activates the corticospinal tract more superficially; therefore, it was evident by the loss of the upper extremity DCMEPs without the loss of lower extremity DCMEPs that the temporary vessel occlusion caused an ischemic event focal to the cortical area perfused by the MCA. This ischemic event was not detected by TCMEP.