Abstracts

Rationale: Frontal lobe epilepsy represents approximately 30% of partial epilepsies seen in epilepsy centers and is the second most common type of epilepsy treated surgically. However, outcome after surgery has been less than satisfying. Possible explanations include the imprecise localizing value of the various seizure patterns originating from the frontal lobes and the presence of a functional network of pathways permitting rapid ictal spread within and outside the frontal lobe making precise localization of ictal onset difficult. Functional near-infrared spectroscopy (fNIRS) is a non-invasive imaging technique of potential value in the study of epileptics. Its temporal resolution (20Hz) offers the possibility to study the evolution of hemodynamic changes occurring during seizures and follow their spatial propagation over time. We report here on the hemodynamic behavior observed in a group of patients with dorsolateral frontal lobe epilepsy. Methods: Patients were diagnosed with dorsolateral frontal lobe seizures based on multimodal analysis of clinical history, video-EEG monitoring, ictal SPECT, EEG-fMRI, MEG-EEG and intracranial recordings. EEG-fNIRS recording using 19 EEG in-house electrodes (EEG video-monitoring; Compumedics, USA) combined with 60 to 140 fNIRS channels (ISS, USA) in order to cover frontal, temporal and parietal lobes bilaterally. Seizure onsets and end times were marked as the earliest and latest scalp electrographic evidence of seizure activity. Hemoglobin concentration variations were calculated and analyzed with the Homer Matlab package and viewing tools developed in-house. Results: Several electrical and electroclinical seizures were successfully recorded using EEG-fNIRS from three patients (age 13 to 43, 2 males /1 female) with refractory dorsolateral frontal lobe epilepsy. All these events were easily distinguishable by fNIRS as independent increases and decreases in fNIRS signal. A great degree of variability was observed both inter subject, and intra subject for successive ictal events. In general however, a significant increase in oxyhemoglobin concentration ([HbO]) is seen at seizure onset over bilateral dorsolateral frontal regions, slightly predominant and earlier ipsilaterally. Concomitantly, mild increases in deoxyhemoglobin concentration ([HbR]) are noted. The initial increase in [HbO] is followed by a significant decrease after a few seconds. In distant temporal and parietal regions, a rapid and sustained decrease in [HbO] is seen. Although seizures were short in duration on scalp EEG, hemodynamic changes inferred by fNIRS were systematically longer. Electrical seizures had better localizing potential than electroclinical seizures because of lesser propagation of hemodynamic changes. Conclusions: Preliminary hemodynamic observations of dorsolateral frontal lobe seizures using EEG-fNIRS suggest a) easily detected rapid changes of [HbO] and [HbR] at onset; b) generally (but not always) earliest in the region of seizure onset and; c) with rapid ipsi- and contralateral propagation, especially with electroclinical seizures as opposed to electrical seizures.