Abstract
Object: Intraoperative transcranial motor-evoked potential (TCMEP) monitorings are widely performed during neurosurgical operations. Alarm points for TCMEP were examined in our series. Methods: TCMEP monitorings were performed during 300 neurosurgical operations. Transcranial stimulations at 100〜600V were delivered by screw electrodes placed in the scalp and electromyographic responses were recorded with surface electrodes on the affected muscles. To exclude the effects of muscle relaxants on TCMEP, compound muscle action potential (CMAP) by supra-maximum stimulation of the peripheral nerve immediately after transcranial stimulation was recorded in 266 operations. Among these 266 patients, 241 patients including 77 cerebral aneurysms, 94 spinal operations, 26 brain tumors, 26 extracranial-intracranial bypass operations, 15 carotid endoarterectomies, 2 intracerebral hematomas, and a arterio-venous malformation, had no preoperative motor palsy. Results: Among 229 patients who had had no preoperative and postoperative definitive motor palsy, the amplitudes of TCMEP compensated by CMAP after peripheral nerve stimulation decreased less than 20% in 4 patients, thus the specificity was 98.3%. Two false negative findings were recognized in 12 patients who had had postoperative newly progressed motor palsy and the sensitivity was 83.3%. Although the threshold for postoperative motor palsy is 80% compensated relative amplitude reduction in both brain tumor and spinal surgery, the alarm point for the operator is considered to be a 70% reduction in all neurological surgery including aneurismal surgeries. Conclusions: Intraoperative TCMEP monitoring is a significantly reliable method to prevent postoperative motor palsy in cranial surgery. A seventy percent reduction of the compensated amplitude is considered to be the alarm point in all neurological surgeries.
