Abstracts

Rationale: Bilateral temporal EEG spikes are frequently observed in patients with temporal lobe epilepsy, and these may be a risk factor against successful epilepsy surgery. Fronto-temporal interictal spikes are also commonly seen in these patients. However, their clinical implications are less well known. The aim of this study is to investigate the importance of epileptiform fronto-temporal EEG features in temporal lobe epilepsy. Methods: We recorded simultaneously 26 channels of scalp EEG with sub-temporal supplementary electrodes and 46-98 channels of intracranial EEG in twelve presurgical candidates with presumed temporal lobe epilepsy who had fronto-temporal as well as temporal spikes on scalp EEG. Subdural electrodes were implanted on the anterior temporal lobe, frontal and orbitofrontal cortex in all patients. We studied the relationship of interictal and ictal discharges among frontal, orbitofrontal, and temporal lobe cortex in these patients. Results: Orbitofrontal cortical spikes that were synchronized with temporal cortical spikes were observed in ten patients. There was no apparent phase delay between orbitofrontal and temporal discharges. Temporally independent orbitofrontal interictal spikes were recorded in seven patients. Early seizure propagation from temporal to orbitofrontal cortex was observed in six patients. Independent orbitofrontal and temporal seizure foci were recorded in one patient. In this patient, seizures that originated in the orbitofrontal cortex propagated exclusively to the ipsilateral temporal lobe and masqueraded clinically as temporal lobe seizures. Conclusions: The frontal-temporal network is commonly involved in the epileptogenesis of temporal lobe epilepsy. Patients with clinical temporal lobe epilepsy who have fronto-temporal EEG spikes frequently have dependent and independent spike sources in the orbitofrontal cortex. Occasionally these patients may have an independent frontal seizure focus that clinically masquerades as a temporal lobe seizure.