Abstracts

Focal cortical dysplasia (CD) is a common cause of focal epilepsy amenable to surgical resection. Complete resection of the dysplastic tissue will result in seizure freedom in a high proportion of patients. The preoperative localization of the epileptogenic zone may require an invasive subdural grid evaluation (SGE). We recently showed that patients undergoing SGE for cortical dysplasia had worse outcomes than expected, compared to patients not undergoing SGE. The goal of our study is to determine the variables that contributed to the poor outcome. The charts and SGE data from thirty-nine patients with isolated CD who underwent SGE-guided epilepsy surgery between 1990 and 2002 were retrospectively reviewed. The success of the surgery was determined by the Engel score at the latest follow-up date. The details of the SGE evaluation were studied: they included the number of grids and electrodes, localization of eloquent cortex and its relationship to ictal and interictal electrodes. The presence of bilateral noninvasive features, diffuse or multifocal onset were also identified. When available postoperative MRI and EEG data were reviewed. Using a multiple regression analysis model, a poor surgical outcome was associated with the following features: postoperative surface EEG interictal epileptiform activity (p=0.0032), [gt]1 grid ictal onset zones (p=0.044), the presence of interictal epileptic activity within eloquent cortex (p=0.00037), a previous SGE (p=0.0041) and bilateral features (on EEG, MRI and/or PET) in the noninvasive evaluation (p=0.0195). A diffuse grid ictal onset, the number of grids used, number of electrodes with interictal or ictal activity (outside eloquent cortex), a non-lesional MRI, and the number of clinical seizure types were not associated with poor surgical outcome. Absence of residual CD on postoperative MRI (when available) did not predict a successful outcome. The occurrence of perioperative complication(s) did not affect the seizure outcome. Careful selection of surgical candidates should result in better postoperative outcomes. The presence of epileptic cortex within eloquent areas, and/or the identification of multifocal/widespread epileptogenicity are associated with worse postoperative outcome. The identification of various predictors of surgical outcome may assist in the risk and benefit counseling of patients in the preoperative period.