P503: Intraoperative language network monitoring by means of cortico-cortical evoked potentials

Abstract

Objective: In order to establish a new intraoperative monitoring for preservation of subcortical language pathways, we applied technique of cortico-cortical evoked potentials (CCEP) during brain surgery. Methods: Subjects were 17 patients with brain tumors located close to the arcuate fasciculus (AF) in the language-dominant left hemisphere. Af- ter craniotomy, electrodes were placed over frontal and parieto-temporal perisylvian areas. Single-pulse stimuli were applied to several pairs of electrodes in the frontal area to record CCEP from the parieto-temporal area. Under general anesthesia, the anterior perisylvian language area (AL) was first defined by CCEP connectivity patterns, and also by presurgical neuroimaging findings. We then monitored the integrity of the language network by stimulating AL and recording CCEPs from the posterior peri- sylvian language area (PL) consecutively during both general anesthesia and awake condition. In the awake condition, language assessment with batteries was also sequentially performed throughout surgical procedures. To confirm language function in AL, high-frequency electrical stimulation (ES) was performed during awake craniotomy in nine patients, who had neither cognitive impairment nor aphasia preoperatively. Results: In all, the CCEP connectivity pattern delineated perisylvian lan- guage network between AL and PL even under general anesthesia. CCEP amplitude declined in two patients (≤32%) during surgical procedures. Two patients had transient language impairment postoperatively. One patient who showed 32% decrease of CCEP amplitude presented phonemic para- phasia during and after operation. Another patient who did not showed decrease of CCEP amplitude developed language impairment immediately after surgery because of brain edema. Language function recovered within a few months in both patients. In all, CCEP monitoring successfully prevented persistent language impairment. In all nine patients who were awakened fully, high-frequency ES confirmed language impairment at AL. Conclusions: Although further accumulated cases will be warranted for establishing the sensitivity and specificity, intraoperative CCEP delineated the perisylvian or dorsal language network and would be useful for online monitoring of subcortical language pathways.