Abstracts

Rationale: Refractory epilepsy is amenable to surgery for seizure freedom. Focal cortical dysplasia (FCD) is a common pathological substrate in MRI negative epilepsy and is difficult to delineate by conventional MRI. Voxel based morphometric (VBM) analysis is an MRI post processing technique and can be utilized to identify hidden epileptogenic lesion on conventional MRIs. Morphometric analysis Program (MAP) is used to perform VBM and has shown utility in identifying FCD in MRI negative refractory epilepsies. However there are no prospective studies suggesting a direct ictal onset zone within the MAP area during invasive monitoring with SEEG. We present pilot data from our ongoing prospective study with currently studied 30 patients with refractory epilepsy to understand direct utility of this technique to identify epileptogenic lesions and determine its role in helping epileptologist in presurgical decision making. Methods: Patients (age range 18-70) undergoing presurgical evaluation at University of Alabama Birmingham for refractory focal epilepsy and required invasive monitoring for further establishment of epileptogenic lesion (in the absence of MRI lesion or if discrepancy between imaging, clinical semiology and EEG) were included in this study. Patients that had failed a prior epilepsy surgery were included if a pre-op MRI was available for analysis. MAP analysis (to identify cortical abnormalities as dysplasia) and FLAIR analysis (modality available in MAP tool) ( to identify hippocampal sclerosis (HS) not identified on conventional MRI) was performed. This data was presented during patient management conference and decision to target MAP lesion (with SEEG electrode) was taken in conjunction with information from other modalities as MEG, PET, and EEG.  Results: Of the 30 patients with refractory epilepsy, MAP lesion was identified in 17 patients (57%) and targeted with a SEEG electrode in 16 patients. Of the 17 patients, 3 had electrodes close to but not within the MAP area. A clear ictal onset zone was identified during SEEG from the MAP lesion in 11 patients (64%) (cingulate, insula, frontal operculum, parahippocampal gyrus, temporal pole, temporooccipital junction, fusiform gyrus, superior and middle temporal gyrus, perisylvian region). 3 patients (10% of total) (one orbitofrontal, superior temporal, cingulate) did not show ictal onset within the MAP lesion (one appeared to have multifocal electrodes involved, one with possible cingulate and 1 clear hippocampal ictal onset). FLAIR analysis showed HS in 8/30 patients, of these 6 patients also had additional MAP lesions. The finding of HS with FLAIR analysis tool showed significant association with ictal onset zone in all 8 patients (100%). Ictal onset zone was identified within the MAP area in 64% of patients with identifiable MAP abnormality, this number increased additionally when FLAIR analysis datasets were combined (8/30). Some patients underwent RNS (for >1 area of ictal onset, eloquent cortex, memory risk) and few (total 5) underwent surgical resection of MAP lesion (an example figure 1) with sustained seizure freedom of 3 -18 months (pathology FCD). For 3 patients post surgical follow up is awaited. Conclusions: VBM analysis helps identify potential epileptogenic areas as FCD in at least 50% of MRI negative refractory epilepsy patients in combination with FLAIR analysis modality to identify hippocampal sclerosis and has good reliability of at least 80%. However further data with higher number of patients is needed to ascertain clear sensitivity and specificity. Funding: No funding