Intraoperative spinal cord monitoring for intramedullary surgery: an essential adjunct.

Intraoperative monitoring of the functional integrity of the spinal cord during removal of intramedullary spinal cord lesions is an aid in intraoperative decision making and a primary tool for the prediction of neurological outcome. Motor evoked potential monitoring has become the neurophysiological monitoring technique of choice for that purpose. In the senior author's experience with over 130 pediatric patients suffering from intramedullary spinal cord tumors, the neurophysiological data of both motor and sensory evoked potentials was utilized in an integrative fashion. Motor evoked potentials, elicited with single transcranial electrical stimuli and recorded directly from the spinal cord with an electrode in the spinal epidural space, reflect the functional integrity of the corticospinal tract. Motor evoked potentials, elicited with a short train of transcranial electrical stimuli and recorded from limb muscles, reflect the functional integrity of the motor system from the cerebral cortex/white matter to beyond the neuromuscular junction. Both epidural and muscle motor evoked potentials correlated closely with postoperative neurological function. Both techniques provide fast, practical and reliable information on the functional integrity of the motor tracts of the spinal cord. No complications attributable to stimulation or recording occurred. Over time both the technique's reliable power of predicting clinical outcome and its practical versatility have altered the surgical approach in that gross total resections are more readily attempted as long as motor evoked potential data indicate the intact functional integrity of the corticospinal tract. This monitoring technique unquestionably had a favorable impact on neurological outcome.