Usefulness and pitfalls of intraoperative spinal motor evoked potential recording by direct cortical electrical stimulation

Objective. The aim of this study is to investigate the usefulness and probl ems with spinal motor evoked potential (MEP) recording, especially the reas ons for failed recording. We report our personal experience over the last 8 years in patients with lesions adjacent to the primary motor cortex. Methods. MEP records of 50 consecutive patients were retrospectively review ed. MEP was recorded by a catheter electrode inserted in the cervical epidu ral space. Stimulation electrodes were placed on the cortical surface durin g surgery. SEP recording was also performed in 29 of 50 patients. Results. MEP was obtained in 40 cases, and SEP was recorded in all 29 cases . The central sulcus was identified in 93% of patients in whom both MEP and SEP were performed, whereas in only 86% of patients who underwent only MEP . The main reason for MEP failure were inadequate exposure of the motor cor tex, pre-existing hemiparesis and technical errors. Postoperative deteriora tion of motor function was closely related to intra-operative MEP changes. Conclusion. MEP is a useful tool to determine the motor cortex and to predi ct postoperative motor function. However, precise pre-operative craniotomy planning and combination with intraoperative SEP is essential to reduce the MEP failure.