Ictal EEG‐fMRI in localization of epileptogenic area in patients with refractory neocortical focal epilepsy

Abstract

SUMMARYPurpose: To evaluate the usefulness of ictal electroencephalography (EEG)-combined functional magnetic resonance imaging ( MRI) (EEG-fMRI) in localizing epileptogenic zone in refractory neocortical focal epilepsy. Methods: From the EEG-fMRI database of our institution including 62 adult patients, 14 (age 18-46 years) experienced some ictal event during the test. Data were segmented into 10-s blocks, and the results were analyzed by contrasting each block to the contiguous 10-s block from the onset of seizure onward, in all cases. In seizures lasting >10 s (five cases), a supplementary analysis was performed, contrasting each block to a baseline condition, in the framework of the general linear model (GLM) of analysis. Regions of activations were compared to results from the different techniques performed during presurgical evaluation, such as SISCOM, positron emission tomography (PET), and invasive subdural EEG monitoring. Key Findings: Regarding the structural MRI findings, nine cases presented some lesion, with blood oxygen leveldependent (BOLD) signal activation placed in the same location in eight of them (89%). SISCOM studies were performed in 11 patients; 5 were concordant with the increase in BOLD signal in a sublobar level, whereas in 3 cases the concordance was in a lobar level. Eleven patients underwent PET studies, being also concordant in a sublobar level in four of them and in a lobar level in four additional cases. Finally, invasive EEG evaluation was performed in three patients and all of them had the seizure-onset zone in the initial area of BOLD activation. Significance: This study adds relevant information to support the integration of EEG-fMRI in the multidisciplinary presurgical workup in patients with refractory epilepsy.

Electroencephalography/functional magnetic resonance imaging responses help predict surgical outcome in focal epilepsy

“…For practical reasons, it is not common to study seizures using fMRI; however, two patients had short electrographic seizures and one had aura during scanning. We included them because such seizures have been shown to provide valuable localization information . This makes our study representative of the fact that seizures are occasionally recorded during EEG‐fMRI studies.…”

The Role of Functional Neuroimaging in Pre-Surgical Epilepsy Evaluation

“…Nevertheless, some studies demonstrated its usefulness for better understanding the hemodynamic correlates involved in the generation and the propagation of the seizures (162, 172–175). The simultaneous recording of video-EEG during ictal fMRI may help to detect BOLD changes associated to the different phases of the seizure (176).…”

Distinct functional and structural MRI abnormalities in mesial temporal lobe epilepsy with and without hippocampal sclerosis

“…The combination of these techniques permits noninvasive simultaneous measurement of neural activity and hemodynamics and allows the study of neurovascular coupling through the variation of BOLD (blood oxygen level–dependent) signal . EEG‐fMRI can reveal hemodynamic changes related to ictal or interictal epileptiform discharges (IEDs), giving insights for the determination of the seizure‐onset zone, but it also provides concomitant pattern of hemodynamic activity of all other brain areas distant from the presumed epileptogenic zone (EZ) . Previous reports of EEG‐fMRI and TLE patients have demonstrated a consistent pattern of IED‐related BOLD responses in areas such as bilateral mesial and neocortical temporal structures but also including extratemporal regions as insula and anterior cingulate .…”