Local epileptogenic networks in tuberous sclerosis complex: a case review

OBJECTIVE: Cortical tubers are a pathognomonic finding in some patients with tuberous sclerosis complex (TSC), and are believed to be epileptogenic foci. Surgery is an effective option in selected patients with TSC who are refractory to medical therapy. This article describes three patients with TSC who underwent three-stage epilepsy surgery at our center, with the intention of examining local electrophysiological changes after each stage of the procedure. METHODS: Magnetic resonance images were obtained after initial implantation of electrodes and after resection and electrode reimplantation. These images were co-registered and overlaid. The intracranial grids were overlaid in a similar procedure and manually traced, and then added to the volumetric image. Mean spike counts were obtained for each patient and expressed in spikes per minute. Statistical analysis was performed on spike counts prior to and after resection. RESULTS: All three patients displayed intense spiking in the regions around the dominant epileptogenic tuber. On tuber removal, spike counts diminished significantly. In each case, new areas of spiking emerged in regions remote from the tuber periphery after tuber resection, with the emergence of secondary ictal onset zones in the resection margin. CONCLUSION: This retrospective study highlights some common electrophysiological features among the patients examined. The observed epileptogenic activity and regions of ictal onset suggest that it may be the region of brain tissue surrounding the tuber that is responsible for the majority of epileptogenic activity in these patients.