W3 Intraoperative monitoring: Spinal cord

Abstract

Surgery at and around the spinal cord places the cord at risk from ischemic, thermal or mechanical injury. The most feared injuries cause motor loss, e.g., paraplegia. Somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) are used for spinal cord intraoperative monitoring (IOM). SEPs are easiest to monitor and were first to gain widespread acceptance. SEP IOM reduced postoperative paraplegia by more than 60%. In the SEP technique, spinal cord pyramidal tract integrity is inferred from SEP posterior column monitoring. Correlations were good, yet some discrepancies occurred between posterior column function and motor outcome. SEPs during myelotomy for spinal cord tumors did not predict motor deficits well. In contrast, MEPs monitor pyramidal tracks directly. Transcranial or direct electrical cortical stimulation produces corticospinal (pyramidal) D and I waves recordable directly from the spinal cord. Limb muscle MEPs can and should bemonitored too. These techniquesmore confidently warn surgeons, and predict and prevent intraoperative injury to the spinal motor pathway. Combining D wave spinal recording with muscle MEPs is a reliable technique. D wave without muscle MEPs has shown false positive changes when assessed in scoliosis surgery, possibly due to recording electrode movement during spinal column distraction. Many users now combine SEP and types of MEP, tailored to the particular patient’s condition, surgery and anesthesia regimen. Further development of IOM techniques could map dorsal and lateral columns of the exposed spinal cord, new tools better to prevent intraoperative spinal injury.