Intraoperative monitoring with somatosensory evoked potentials in neurosurgical operations on the spinal cord

Our report deals with 24 patients who were treated neurosurgically for spinal space occupying lesions and in whom a noninvasive technique of intraoperative monitoring with somatosensory evoked potentials (SEP) was carried out. Reproducible potentials were obtained intraoperatively in each case, but only patients in whom potentials could be obtained preoperatively were included in the study. Using changes in amplitudes of up to 50% of the starting value as criteria, it was possible to make an accurate statement as to the expected postoperative neurological status in 22 patients (91.7%). We found false positive results in 2 cases (8.3%), but no false negative results were observed. In one patient, a postoperative complication caused by bleeding could be discovered in the early stages by means of postoperative SEP-monitoring. The results confirm the reliability and usefulness of this noninvasive technique when applied intraoperatively. Furthermore, the value of SEP-monitoring during the early postoperative phase in cases where the clinical judgment is limited due to anesthesia is emphasized. The secondary postoperative deterioration in the neurological status of one patient with a ventral space occupying lesion could not, however, be detected with the SEP monitoring. The use of the motor stimulation technique could be an advantageous adjunct in intraoperative and perioperative monitoring, particularly in cases where primarily motor pathways are at risk.