Subdural electrodes in focal epilepsy surgery at a typical academic epilepsy center

To assess the use of subdural intracranial EEG (iEEG) on postoperative outcomes at an epilepsy center.

Ninety-one epilepsy patients underwent iEEG. Array design was compared with noninvasive EEG with over 1 year of outcome. Patient demographics, implanted brain sites, electrodes, contacts/site, and surgical location were correlated with outcome. Fisher exact test and logistics regression were used to evaluate significance (P ≤ 0.05).

Of ninety-one women, 55 (mean age, 32.3 years; range, 11-60) underwent tailored iEEG. Seventy of ninety-one (76.9%) resections (70% temporal) yielded 24/91 (26.4%) seizure free (SF). Strips (57.1%), grids (5.5%), or both (37.4%) for iEEG use was commonly bilateral (58.2%; 65.3% bitemporal) but did not predict outcome (P = NS). A lesion (28/91) did predict a SF outcome (42.9%). The iEEG localized 45.7% of seizures beyond scalp EEG and changed the localization or lateralization in 75.7% of resected patients. Electrode design, localization, lateralization, and site of resection did not correlate with outcome (P = NS). Overall, iEEG use portended a non-SF outcome (P ≤ 0.0001).

The use of iEEG selected 46% additional patients for surgery, yet only 26% became SF. A magnetic resonance imaging lesion predicted a SF or seizure-improved outcome. Although iEEG changed the localization and lateralization of scalp ictal EEG in three quarters of patients, its use was a negative predictor for a favorable outcome. Preoperative counseling should emphasize expectations for seizure reduction in patients requiring iEEG.