Significance of spikes recorded on intraoperative electrocorticography in patients with brain tumor and epilepsy

PURPOSE: Patients with medically intractable epilepsy due to brain tumors may undergo resective surgery for treatment of both the tumor and the epilepsy. In this instance, the extent of surgical resection is sometimes guided by spikes recorded on intraoperative electrocorticography (ECoG). Whether spikes recorded by electrocorticography imply active epileptogenicity has not been addressed adequately. METHODS: We performed preresection and postresection electrocorticography on 36 patients with brain tumor and seizures. There were 31 low-grade gliomas, 4 high grade gliomas, and 1 dysembryonic neuroepithelial tumor. Patients had resection of the tumor to normal tissue margins only. No additional surgery was performed, based on electrocorticography findings. Patients were divided into 2 groups: Group I (no seizures or rare seizures after resection) and Group II (recurrent seizures). Recorded spikes were analyzed for spike distribution and spike discharge rate. RESULTS: On preresection ECoG, 85% of patients in Group I and 88% of patients in Group II had spikes. In Group I, 70% of patients had spikes over the tumor bed, and 63% of patients had spikes in the surrounding tissue. In Group II, 55% of patients had spikes over the tumor bed and 89% of patients had spikes in the surrounding tissue. Spike distribution and discharge rate did not correlate with outcome. On postresection ECoG, 60% of patients in Group I and 67% of patients in Group II had residual spikes. In Group I, 46% of patients had spikes along the margin of resection and 26% of patients had extramarginal spikes. In Group II, 50% had spikes along the margin of resection and 67% of patients had extramarginal spikes. CONCLUSIONS: The difference in spike distribution in the extramarginal area between the 2 groups was not statistically significant, but showed a trend toward a relationship between postresection spikes and seizure recurrence.