Abstracts

Rationale: Determination of epileptogenic zone in planned resective surgery for focal onset seizures can be difficult. Typically spike and wave activity and fast beta activity are considered the primary features for localization of seizure onset in intracranial EEG monitoring. With the extensive use of subdural electrodes, there have been reports of electro-decrement in certain regions of the grids seen prior to the onset of the spike and wave complexes or beta activity. Our results show that attention to the region of the onset of electro-decrement can aid in determining the extent of the epileptic zone. Methods: A review was done of the intracranial EEG monitoring findings in 4 patients who presented for resective surgery, ages 4- 19. In all of these patients, electro-decrement occurred just before spike and wave complexes or fast beta activity. Results: The localization of the decrement aided in the determination of the epileptogenic zone and the extent of resection. In two patients, the extent of resection of epileptogenic zone in the first surgeries did not take into account the entire extent of the decrement prior to the spike onset. These two patients underwent 2nd surgeries with Engel 1A and 1D outcomes.* The other two patients achieved Engel 1A outcome after the initial resection. Of the two who underwent one resection, one had a right fronto-temporal resection, one underwent right medial-frontal resection. The other two were left temporal resections with subsequent extension of previous surgery.* seizures with fever/illness only & neurocutaneous disorder Conclusions: Spike and fast beta bursts (buzz) are not the only important factors in determining the seizure onset zone or epileptogenic zone in epilepsy surgery. Decrement on intracranial monitoring is a useful marker for seizure onset and determination of the epileptogenic zone, frequently suggesting either a larger zone or deeper focus, thereby aiding in surgical planning.