Abstracts

Rationale: The preservation of brain functions during surgery still poses a challenge in patients with brain tumors or epileptic lesion at or close to the eloquent areas. Although various neuroimaging and electrophysiological techniques are known to be effective for functional mapping and monitoring brain functions, difficulties are associated with identifying subcortical fibers with no clear landmarks. We herein developed the novel technique of cortical evoked potentials with subcortical stimuli (subcortical-cortical evoked potentials: SCEP) in order to identify subcortical fibers intraoperatively.Methods: After resection, a 1x4-electrode plate was placed on the floor of the removal cavity and 1-Hz alternating electrical stimuli were delivered to this electrode. A 4x5 recording electrode plate was placed on the central areas to map the pyramidal tract and temporo-parietal areas for the arcuate fasciculus. Cortical evoked potentials were obtained by averaging electrocorticograms time-locked to the stimulus onset.Results: We used this technique to identify the pyramidal tract in four patients, arcuate fasciculus in one patient and both in one patient during surgical procedures. In five out of the six patients, the subcortical stimulation within 15 mm of the target fiber induced cortical evoked potentials in the corresponding areas.Conclusions: This technique was useful for identifying subcortical fibers, which are difficult to detect with standard cortical stimulation mapping. It is expected to contribute to the effectiveness and safety of resective surgery in patients with lesions close to eloquent areas.