Scalp recorded somatosensory evoked potentials in response to cauda equina stimulation in neurosurgical operations on the spinal cord.

Somatosensory evoked potentials were recorded from the scalp in response to cauda equina stimulation in a total of 30 patients who were treated neurosurgically for spinal space-occupying lesions. Reproducible potentials could be obtained intraoperatively in 26 patients (86.7%). Preoperatively all of the four remaining patients had severe neurological deficits and an incomplete para- or tetraparesis. On the basis of an acceptable amplitude reduction of up to 50% at the end of the operation, it was possible to make an accurate statement as to the expected postoperative neurological state in all of the 26 patients in whom potentials could be obtained intraoperatively. There were no false positive or false negative findings. Our results confirm the reliability and usefulness of this invasive stimulation and non-invasive recording technique when applied intraoperatively.