Abstracts

Cortical tubers are the hallmark of tuberous sclerosis complex (TSC) and are usually associated with overlying and surrounding gray matter on MRI. In the present study, we have quantitatively analyzed ictal electrocorticography (ECoG) data using subdural and depth electrodes to determine whether epileptic seizures originate more frequently from glucose hypometabolic cortex surrounding a tuber than normometabolic cortex. Secondly, we asked whether epileptic seizures are generated by a cortical tuber itself or the cortex surrounding a tuber in children with TSC. We studied a series of 16 children with TSC and uncontrolled seizures (age: 5 months to 16 years; 11 boys), who underwent MRI, glucose metabolism PET and prolonged intracranial ECoG recording for subsequent cortical resection. The location of electrodes was derived from planar X-rays and displayed on the 3D brain surface reconstructed from MRIs showing the location of tubers and also hypometabolic areas from co-registered PET scans (Muzik et al, Neurology 2000). For each seizure event, the center of ictal discharges was objectively defined as the electrode showing the maximal increase of ECoG magnitude specific to an ictal onset in a seizure consisting of continuous rhythmic activity or the electrode showing the maximal spike magnitude in a seizure consisting of periodic spike activity or a single spike followed by fast wave bursts (Asano et al, Epilepsia 2005 [in press]). We performed a one-sample t-test to determine whether the center of ictal discharges was located more frequently in glucose hypometabolic regions than normometabolic regions, and whether the center of ictal discharges was located more frequently in the cortex surrounding a tuber than the cortical tuber itself. A total of 70 seizures were objectively analyzed in the subjects where subdural electrodes but not depth electrodes were placed on the presumed epileptic hemisphere. In 57 out of the 70 seizures, the center of ictal discharges was located in the glucose hypometabolic cortices. Ictal discharges arose more frequently from the glucose hypometabolic cortex than from normometabolic cortex (p[lt] 0.001). In a single subject where a depth electrode was inserted into a tuber, no spontaneous seizures were captured and we were not able to determine the location of ictal onset zones. These results suggest that most of the epileptic seizures in children with TSC may be generated by glucose hypometabolic regions associated with either the dysplastic cortex surrounding a tuber or the tuber itself. Further studies of patients with depth electrodes are required to determine whether epileptic seizures are generated by a cortical tuber itself or the cortex surrounding a tuber in children with TSC. (Supported by NIH: K23NS047550.)