Monitoring Cortico-cortical Evoked Potentials Using Only Two 6-strand Strip Electrodes for Gliomas Extending to the Dominant Side of Frontal Operculum During One-step Tumor Removal Surgery

Resection of the dominant side of gliomas extending to the frontal operculum has a high-risk of permanent language dysfunction. Here, we report recording cortico-cortical evoked potentials (CCEP) using only two 6-strand strip electrodes to monitor language-related fibers intraoperatively. We examined whether this simple procedure is useful for removing gliomas extending to the dominant side of frontal operculum. This study included five cases of glioma extending to the left frontal operculum. The frontal language area (FLA) was first identified by functional mapping during awake craniotomy. Next, a 6-strand strip electrode was placed just above the FLA, while on the temporal lobe side, an electrode was placed so as to slide parallel to the Sylvian fissure toward the posterior language area. Electrical stimulation was performed using the electrode on the frontal side, and CCEPs were measured from the electrode on the temporal side. CCEPs were detected in all cases. Immediately after surgery, all patients demonstrated language dysfunction to varying degrees. CCEP decreased up to 10% in one patient, who recovered language function after 24 months. CCEP decreased slightly up to 80% in one, and in the three other cases, CCEPs did not change. These four patients soon recovered language function within 2 weeks to 1 month. This study confirmed the utility of CCEP monitoring using only two 6-strand strip electrodes during one-step surgery. We believe this simple method helped in monitoring intraoperative language function and aided predicting its postoperative recovery, in patients with gliomas extending to the dominant side of frontal operculum.