Abstracts

Rationale: Although epileptogenic cortical dysplasias (CD) usually appear as discrete MRI lesions, resective surgery reduces seizures significantly in only 67% (Bingaman and Catalepe, 2001). To investigate this discrepancy, pre-operative EEGs of 50 consecutive patients who underwent resective surgery for CD-related intractable focal epilepsy were reviewed. Methods: The entry criterion was demonstration of one or more types of CD disclosed by histological review of resective specimens. Sufficiently congruent data for seizure localization from semiology, EEG and MRI were required for surgical candidature. Archived EEG reports were scrutinized for localization of epileptiform (ictal and interictal) and non-epileptiform abnormalities. Results: Several EEG abnormalities reflected widespread cortical dysfunction: 1) independent bi-hemispheric abnormalities (spikes, delta, theta) in 25 (50%), 2) EEGs of 22/25 (88%) had focal spikes in each hemisphere , and 3) 14/50 (28%) had spike-waves (SWs) or other bisynchronous epileptiform patterns. Abnormalities were more widespread in extra-temporal (ET) than temporal (T) patients: 1) greater average number of lobes with focal spikes (mean= 3.14 (ET) vs.2.14 (T); p=0.02), and 2) higher incidence of SWs (5/23=22% for ET vs. 0/15 for T). Conclusions: Multifocal and bilateral EEG abnormalities, common among patients undergoing resective surgery for CD-based intractable epilepsy, may underlie less than expected surgical effectiveness.