Monitoring of Short-latency Somatosensory Evoked Potentials during Surgery for Cervical Cord and Posterior Fossa Lesions

—Changes in Subcortical Components—

Abstract

Short-latency somatosensory evoked potentials (SSEPs) following median nerve stimulation were monitored intraoperatively in 23 patients with cervical cord or posterior fossa lesions. The SSEPs consisted of four subcortical potentials (P9, P11, P13, and N16) prior to the appearance of the cortical potentials. Potentials were also directly recorded from the surgical fields in some cases. Loss of components due to surgical procedures was regarded as abnormal, and the changes in SSEPs correlated well with the generating source of each component. Postoperative neurological deficits were noted in four of the nine patients who had changes in SSEPs or directly recorded potentials, but in three cases the deficits were transient. The authors conclude that monitoring of subcortical potentials is useful in detecting interruption of medial lemniscal pathways during surgery.