Somatosensory-Evoked Potential Asymmetry in Medullary Ischemia During Cervical Spine Surgery

This report describes how somatosensory-evoked potentials (SEPs) can detect acute medullary ischemia during cervical spine surgery. This article describes how asymmetric SEP intraoperative monitoring changes can localize medullary ischemia. Localization of change was validated by postoperative magnetic resonance imaging (MRI). A 68-year-old man underwent cervical posterior fusion with monitoring of bilateral SEPs of the upper and lower extremities. The SEPs disappeared during initial exposure of the C1 lamina. Changes were asymmetric in degree and duration. Brain MRI postoperatively demonstrated bilateral posterior inferior cerebellar artery (PICA) territory infarcts involving the left lateral medulla. This illustrates how intraoperative SEP monitoring can provide important information on the functional integrity of brainstem structures even during cervical surgery. A knowledge of medullary anatomy and vascular territories is necessary for interpreting SEP changes. In cervical surgery, SEPs incidentally monitor the integrity of the brainstem while monitoring the spinal cord. The asymmetry of SEP change seen here was consistent with medullary level impairment, where the vascular territory is lateralized in contrast to the symmetric anterior spinal artery territory.