Attenuation of somatosensory evoked potentials during positioning in a patient undergoing suboccipital craniectomy for Chiari I malformation with syringomyelia.

Intraoperative electrophysiologic monitoring can diminish the risk of neurologic injury by enabling the detection of injury at a time when it can be reversed or minimized. This report describes a 14-year-old girl with a Chiari's malformation type I and syringomyelia who underwent a suboccipital decompression and dural patch grafting with concurrent somatosensory evoked potentials. When the patient was turned into the prone position and the neck was flexed, the left-sided somatosensory evoked potential deteriorated. After the patient's neck was repositioned, the left median nerve potential improved but did not return to baseline. Postoperatively, the patient had decreased proprioception of her left arm, which completely resolved at 2-week follow-up. This single case report does not establish the need for routine somatosensory evoked potential monitoring. Nevertheless, deterioration of the potential in this case led directly to a change in the surgical positioning, which may have significantly reduced the chances of a permanent neurologic injury.