Abstracts

Rationale: Gliomas are highly epileptogenic tumors, resulting in seizures that are refractory to medications in 30-50% of cases, and adversely affecting patients' quality of life. While complete surgical resection is known to be a predictor of improved seizure control, less well studied is the role in seizure outcome provided by electrophysiological identification of epileptogenic tissue at the time of tumor resection. Methods: We retrospectively analyzed data from 1910 tumor resections in 1640 patients from 2004 to 2014, dividing them for purposes of analysis into three groups: (1) glioneuronal tumors, (2) low-grade gliomas, and (3) high-grade gliomas. We examined the number and frequency of seizures and anti-epileptic drugs (AEDs) before and after resection, and compared these data between groups. We studied the occurrence of seizures based on the natural history of the tumor, in some cases over the course of multiple resections and oncological treatments. In cases of post-operative seizure freedom, we looked at time to AED withdrawal wherever applicable. We also examined pre-operative EEG, or extraoperative or intraoperative electrocorticography (ECoG), and compared post-operative seizure outcomes in patients with or without ECoG. Results: Our cohort consisted of 46% men and 54% women, with 1502 high-grade gliomas, 347 low-grade gliomas, and 61 glioneuronal tumors. 83% of glioneuronal tumors, 79% of low-grade gliomas, and 69% of high-grade gliomas had seizures prior to resection. Seizure reduction at 6 and 12 months after resection was 88% and 80% for high-grade gliomas, while 13% had an increase in seizures post-operatively (usually with recurrence of disease). For low-grade gliomas, seizure reduction at 6 and 12 months was 100% and 95% with 10% having increased or new-onset seizures. Mean duration of follow-up for low-grade gliomas was 4 years, while it was 3 years for high-grade gliomas. 28% of patients with low-grade gliomas who became seizure free after tumor resection were able to discontinue AEDs. However none of the patients with high-grade gliomas were able to discontinue AEDs after resection. Less than 10% of patients in the low-grade group, and less than 5% in the high-grade group, had electrocorticography preoperatively or intraoperatively for the purpose of identifying potentially epileptogenic tissue. Conclusions: Seizures are often the presenting symptom of glioma, or the harbinger of recurrence. Our findings support that seizures are more common in glioneuronal tumors and low-grade gliomas, and suggest that short-term post-operative seizure control is improved in low-grade gliomas. Very few surgical resections were guided by the use of neurophysiological methods to determine localization of epileptogenic zone. There is little evidence from the studies to date on whether pre-operative epilepsy evaluation or intraoperative ECoG guiding tumor resection improves post-operative seizure outcome, however we intend to discover whether there is a significant improvement in seizure outcomes post-operatively for those patients who have a pre-operative epilepsy evaluation or intraoperative ECoG to assist in resection planning.