Researchers at the University of Calgary and Alberta Children's Hospital, Canada studied histochemically frozen sections of 10 brain resections from 7 epileptic children (ages 2 months to 17 years). None had mitochondrial disease; 1 had tuberous sclerosis and 2 hemimegalencephaly. Preop EEG and intra-operative ECoG defined foci refractory to AEDs. Increased mitochondrial respiratory chain enzymes were demonstrated in individual neurons of hippocampal and neocortex epileptic foci. These intensely staining neurons may indicate functional hypermetabolism and represent a metabolic marker of an epileptic focus. Alpha-B-crystallin was also strongly reactive, demarcating the epileptic focus as a wide field. [1]

COMMENT. Metabolic tissue markers of epileptic foci help define a total excision of brain tissue in the surgical management of refractory epilepsies. Increased mitochondrial respiratory chain enzymes and/or intense a-B-crystallin reactivity at the periphery of resected brain tissue may indicate incomplete removal of a focus and an increased risk of seizure recurrence [2]. These novel tissue markers add immunohistochemistry to EEG telemetry, ECoG, and MRI as tools to determine the extent of resection of epileptic foci of brain tissue.

Epileptic networks in focal cortical dysplasia revealed by EEG and fMRI. Of 23 patients with focal cortical dysplasia and epilepsy undergoing presurgical evaluation with intracranial EEG (icEEG) and simultaneous EEG-fMRI, 12 had interictal discharges (IED) during recording, and 11 of 12 had IED-related hemodynamic changes. The fMRI results were concordant with the seizure onset zone (SOZ) on icEEG in 5 of 11 patients. Four of 5 had >50% reduction in seizure frequency following resective surgery. The remaining 6 had discordant IED-related fMRI signal change. Five of 6 had a poor surgical outcome. Discordant regions of IED-related hemodynamic change are associated with a widespread seizure onset zone and poor surgical outcome. [3]