SIGNIFICANCE OF SPIKES RECORDED ON INTRAOPERATIVE ELECTROCORTICOGRAPHY IN PATIENTS WITH BRAIN-TUMOR AND EPILEPSY

Purpose: Patients with medically intractable epilepsy due to brain tum ors may undergo resective surgery for treatment of both the tumor and the epilepsy. In this instance, the extent of surgical resection is so metimes guided by spikes recorded on intraoperative electrocorticograp hy (ECoG). Whether spikes recorded by electrocorticography imply activ e epileptogenicity has not been addressed adequately. Methods.-We perf ormed preresection and postresection electrocorticography on 36 patien ts with brain tumor and seizures. There were 31 low-grade gliomas, 4 h igh grade gliomas, and 1 dysembryonic neuroepithelial tumor. Patients had resection of the tumor to normal tissue margins only. No additiona l surgery was performed, based on electrocorticography findings. Patie nts were divided into 2 groups: Group I (no seizures or rare seizures after resection) and Group II (recurrent seizures). Recorded spikes we re analyzed for spike distribution and spike discharge rate. Results: On preresection ECoG, 85% of patients in Group I and 88% of patients i n 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 residua l spikes. In Group I, 46% of patients had spikes along the margin of r esection and 26% of patients had extramarginal spikes. In Group II, 50 % had spikes along the margin of resection and 67% of patients had ext ramarginal spikes. Conclusions: The difference in spike distribution i n the extramarginal area between the 2 groups was not statistically si gnificant, but showed a trend toward a relationship between postresect ion spikes and seizure recurrence.