Definition and localization of the epileptogenic zone Definition of the epileptogenic zone in a patient with non-lesional temporal lobe epilepsy arising from the dominant hemisphere

Pharmacoresistant epilepsy arising from the dominant temporal region in patients with intact memory and normal anatomical imaging, presents major challenges in the preoperative definition of the epileptogenic zone, and the planning of the extent of the surgical resection. We report on the case of a 42-year-old, right-handed male who presented with recurrent daily seizures that were resistant to antiepileptic drugs. Multiple, non-invasive (scalp) video-EEG evaluations revealed focal epilepsy arising from the left fronto-temporal region. Multiple high resolution MRIs that were performed at multiple Epilepsy Centers failed to show any abnormality. Fluoro-deoxyglucose PET scan showed extensive, left antero-mesial temporal hypometabolism, and ictal SPECT showed increased perfusion in the left insula in addition to the left mesial and anterior temporal pole. Neuropsychological testing and intracarotid methohexital testing revealed excellent memory to the left, dominant side. A two-stage invasive evaluation with subdural grid electrodes followed by depth electrode recordings allowed the localization of the epileptogenic region to the temporal pole. A selective resection of the left temporal pole (that spared the hippocampal formation) resulted in a seizure-free outcome (one year follow-up) with no significant consequences on memory function. We conclude that targeted, invasive recording techniques should be used for the accurate localization and delineation of the extent of the epileptogenic zone in cases of suspected, non-lesional, dominant hemisphere, temporal lobe epilepsy with preserved memory function. The use of the staged invasive approach may increase the chances for memory (function) sparing through tailored, temporal resection.