Abstracts

Simultaneous subdural grid and intracerebral depth electrode recordings offer a precise method of seizure localization in patients with temporal lobe epilepsy undergoing evaluation for surgical resection. However, the clinical significance and association with pathologic findings remains to be defined. We reviewed data from all temporal lobectomy patients at the University of Maryland Medical Center who underwent simultaneous grid and depth electrode monitoring. All patients required intracranial monitoring either for language mapping or for further localization of seizure onset. We reviewed all electrophysiologic data and correlated localization of seizure onset with subsequent pathologic findings on resected tissue. We analyzed 63 temporal lobectomy patients with simultaneous grid and depth electrode monitoring. Adequate pathology and EEG data were available for 41 patients. Intracranial subdural grid and intracerebral depth electrode monitoring revealed mesial onsets in 27 patients (66%) and lateral onsets in 9 patients (22%). 5 patients had both lateral and mesial onsets (12%). On pathology, 35 patients (85%) were found to have mesial temporal abnormalities, and 6 patients (15%) had normal mesial temporal pathology. Mesial temporal onset on electrophysiologic evaluation was seen with subsequent mesial pathology in 25 of 27 patients (93%). Lateral temporal onset was associated with no mesial pathology in 3 of 9 patients (33%). Although a higher percentage of patients with mesial temporal pathology had mesial seizure onset, this was not statistically significant. Findings of mesial EEG onset and mesial pathology were predictive of seizure freedom and were seen in 18 of 25 patients (72%). Patients with mesial pathology were more likely to be seizure free with 22 of 35 (63%) having Engel Class I outcomes. Also, patients with mesial temporal onsets were more likely to be seizure free (70%) than other patients (43%). Mesial temporal pathology was found in 85% of temporal lobectomy patients who underwent combined subdural grid and intracerebral depth electrode recording. Although a higher percentage of patients with mesial seizure onsets had mesial pathology, this did not reach statistical significance. Patients with mesial EEG onsets had the best outcomes. Different pathologists performed the analyses over several years, and this may have limited our pathologic correlations. Still, the results of combined subdural grid and intracerebral depth electrode monitoring are promising, providing a method of precise localization of seizure onset and prediction of clinical outcomes.