Combined motor and somatosensory evoked potential monitoring for intramedullary spinal cord tumor surgery: correlation of clinical and neurophysiological data in 17 consecutive procedures

Abstract

The primary objective of neurophysiologic monitoring during surgery is to prevent permanent neurological sequelae. We prospectively evaluated whether the combined use of somatosensory- and motor-evoked potential (SEP/MEP) for intramedullary spinal cord tumor (IMSCT) surgery may be beneficial. Combined SEP/MEP monitoring was attempted in 20 consecutive procedures for IMSCT operations. Trains of transcranial electric stimulation over the motor cortex were used to elicit MEPs from limb target muscles. The tibial and median nerves were stimulated to record SEP. The operation was paused or the surgical strategy was modified in every case of significant SEP/MEP changes. Combined SEP/MEP recording was successfully achieved in 17 of 20 (85%) operations. In 3 of 17 operations, SEP and MEP were stable, and all patients remained neurologically intact after surgery. Significant MEP changes were recorded in 12 operations (70%). In 7 of these 12 operations, MEP recovered to some extent after surgical intervention, and these patients showed no neurological changes. In the remaining 5 operations, MEP did not recover and the patients had a transient (n = 2) or a permanent (n = 1) motor deficit. Significant SEP changes with stable MEP were related to a transient hypesthesia. Combined SEP/MEP monitoring provided higher sensitivity, and higher positive and negative predictive value than single-modality techniques. Detection of MEP changes and adjustment of surgical strategy may prevent irreversible pyramidal tract damage.

Key words:

• Motor-evoked potentials
• somatosensory evoked potentials
• intraoperative neurophysiologic monitoring
• spinal cord surgery