Abstracts

Rationale: Functional MRI (fMRI) with simultaneous EEG recording could theoretically be a good tool for detecting functional changes occurring at seizure initiation within the epileptogenic zone due to its ability to detect subtle changes in cerebral activity with a very high spatial and temporal resolution. Therefore, our working hypothesis was sequential analysis of the BOLD signal changes seizure-induced could be applied to improve the localization of the ictal onset zone and might enable investigation of the hemodynamic and metabolic correlates of epileptic seizure activity with high spatial and temporal resolution. Methods: For that purpose, we analyzed five independent focal seizures from five patients with pharmacorresistant epilepsy who experimented partial seizures during ictal-fMRI scanning as part of their presurgical evaluation. For each individual seizure, t-maps were calculated continuously, from 120 seconds before the clinical/EEG seizure onset onwards, by comparing two consecutive groups of 5 images. The time lag between each comparison was 2 seconds. Subsequently, the results were compared with those of subtraction ictal SPECT coregistered with MRI (SISCOM) and intracranial EEG in order to evaluate the utility of fMRI in the anatomic location of the seizure onset zone. Results: After sequential analysis, a well-localized and statistically significant (t-values ranging between 7-14) area of increase-signal was found on each analyzed seizure. This, invariably, preceded the clinical/electrical seizure onset in several seconds (6 to 52 seconds); was concordant with SISCOM results in all but one patient (4/5), in whom SISCOM results probably represent some degree of seizure propagation; and, perfectly matched the ictal onset zone determined by intracranial EEG (2/2). Complete resection of the preoperatively well-localized initial area of increased in signal resulted in seizure remission in 75% (3/4). Conclusions: Sequential analysis of ictal fMRI-data might be a useful tool to delineate precisely and non-invasively where the ictal onset zone is located within the brain, which is crucial in the presurgical evaluation of pharmacoresistant epileptic patients.