Intraoperative cortico-cortical evoked potentials for language monitoring in epilepsy surgery.

OBJECTIVE To evaluate the applicability of cortico-cortical evoked potentials (CCEP) for intraoperative monitoring of the language network in epilepsy surgery under general anesthesia. To investigate the clinical relevance on language functions of intraoperative changes of CCEP recorded under these conditions. METHODS CCEP monitoring was performed in 14 epileptic patients (6 females, 4 children) during resections in the left perisylvian region under general anesthesia. Electrode strips were placed on the anterior (AL) and posterior (PL) language areas, identified by structural and functional MRI. Single-pulse electrical stimulations were delivered to pairs of adjacent contacts in a bipolar fashion. During resection, we monitored the integrity of the dorsal language pathway by stimulating either AL by recording CCEP from PL or vice versa, depending on stability and reproducibility of CCEP. We evaluated the N1 component of CCEP before, during and following resection. RESULTS All procedures were successfully completed without adverse events. The best response was obtained from AL during stimulation of PL in 8 cases and from PL during stimulation of AL in 6 cases. None of 12 patients with a post-resection N1 amplitude decrease of 0-15% from baseline presented postoperative language impairment. Decreases of 28% and, respectively, of 24% of the N1 amplitude were observed in two patients who developed transient postoperative speech disturbances. CONCLUSIONS The application of CCEP monitoring is possible and safe in epilepsy surgery under general anesthesia. Putative AL and PL can be identified using non-invasive presurgical neuroimaging. Decrease of N1 amplitude >15% from baseline may predict postoperative language deficits.