Loss of evoked potentials during spinal surgery due to spinal cord hemorrhage.

The cortical somatosensory evoked potential (SEP) disappeared during corrective spinal surgery in a patient with muscular dystrophy. The patient died 18 hours after surgery. Autopsy revealed an intramedullary hemorrhage 4 mm in diameter in the posterior horn of the cervical spinal cord. Microscopically, hypoxic neurons were seen adjacent to the hemorrhagic area, implying that the lesion was at least 6 hours old. The hemorrhage corresponded to the loss of SEPs and confirms that spinal cord monitoring can detect such lesions.