False lateralization of seizure onset by scalp eeg in non-lesional temporal lobe epilepsy:A surgical case report

Abstract

Temporal lobe epilepsy-TLE-often presents bilateral epileptiform discharges on an electroencephalogram (EEG). Epileptic seizures originating in the hippocampus can be propagated to the contralateral hippocampus earlier than to the ipsilateral temporal neocortex, so that careful investigation is necessary to determine the side of epileptic focus in TLE. A 35-year-old right-handed male was referred for surgical treatment of epilepsy. He started to have complex partial seizures at age 20, which were resistant to multiple antiepileptic medications. Brain MRI and interictal FDG-PET were both normal. Long-term video-EEG monitoring revealed bilateral temporal spikes interictally with ictal EEG changes starting in the right temporal region. Depth and subdural electrodes were implanted to the bilateral hippocampi and temporal neocortices to determine the laterality of the seizures. The invasive EEG revealed epileptic seizures originating in the left medial temporal structures with secondary propagation to the contralateral hippocampus. Left anterior temporal lobectomy and amygdalohippocampectomy rendered him seizure free for 12 months. Histopathological diagnosis was type-cortical dysplasia associated with mild hippocampal sclerosis. Scalp EEG occasionally presents the first ictal changes in the contralateral side to the epileptic focus in TLE. There fore careful presurgical evaluation with bilateral depth and subdural electrodes is important to determine the laterality of the epileptic focus in TLE, especially when the neuroimaging study shows no obvious abnormalities.