Abstracts

RATIONALE: To determine the relationship between neuroimaging (structural, functional) abnormalities and chronic subdural EEG abnormalities in children with tuberous sclerosis complex (TSC). METHODS:_: Four children (age: 1.1-9.5 year; 1 boy, 3 girls) with TSC and intractable epilepsy underwent MRI, PET with 2[F18]fluoro-2-deoxyglucose (FDG), chronic subdural EEG monitoring and subsequent resective surgery (3 Class I outcome, 1 Class III; mean follow-up 17 months). Subdural electrode location was determined on 3D MRI image volumes. Hypometabolic cortical areas were objectively defined based on 10% asymmetry with homotopic cortical areas or 10% difference with adjacent normal cortex if homotopic cortex was lesional. Electrodes (N=339) were classified as (i) tuber region (ii) hypometabolic region and (iii) normal region (normal MRI and FDG PET). Percent of electrodes showing "epileptic" activity (either ictal or frequent interictal epileptiform discharges) of total electrodes for each region type was calculated. RESULTS:_ Twenty-five percent (17/68) of electrodes in the tuber region showed "epileptic" activity; all but 4 "epileptic" electrodes were at tuber borders. Percent of "epileptic" electrodes for the hypometabolic and normal regions were 56% (55/99) and 26% (43/172), respectively. The hypometabolic regions had a higher percent of "epileptic" electrodes than the tuber (p<0.0001) and normal regions (p<0.0001). Neuropathology of normal tissue regions showing "epileptic" activity displayed either mildly hypercellular cortex with abnormal lamination or scattered hamartomatous lesions with balloon cells. CONCLUSIONS:_ Our results show that the main epileptogenic zones in TSC are the hypometabolic regions surrounding tubers. However, cortical regions with normal MRI and FDG PET adjacent to the tuber and hypometabolic zones may also be dysplastic and participate in ictal onset and frequent interictal epileptiform activity.