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

Abstract

SUMMARYPurpose: Simultaneous electroencephalography/functional magnetic resonance imaging (EEG/fMRI) recording can noninvasively map in the whole brain the hemodynamic response following an interictal epileptic discharge. EEG/fMRI is gaining interest as a presurgical evaluation tool. This study aims to determine how hemodynamic responses related to epileptic activity can help predict surgical outcome in patients considered for epilepsy surgery. Methods: Thirty-five consecutive patients with focal epilepsy who had significant hemodynamic responses and eventually surgical resection, were studied. The statistical map of hemodynamic responses were generated and coregistered to postoperative anatomic imaging. Patients were classified into four groups defined by the relative relationship between the location of the maximum hemodynamic response and the resection: group 1, fully concordant; group 2, partially concordant; group 3, partially discordant; and group 4, fully discordant. These findings were correlated with surgical outcome with at least 12-month follow-up. Key Findings: Ten patients in group 1 had the maximum t value (t-max) inside the resection; nine in group 2 had the t-max outside but close to the resection and the cluster with t-max overlapped the resection; five in group 3 had the t-max remote from resection, but with another less significant cluster in the resection; and 11 in group 4 had no response in the resection. The degree of concordance correlated largely with surgical outcome: a good surgical outcome (Engel's class I) was found in 7 of 10 patients of group 1, 4 of 9 of group 2, 3 of 5 of group 3, and only 1 of 11 of group 4. These results indicate that the partially concordant and partially discordant groups are best considered as inconclusive. In contrast, in the fully concordant and fully discordant groups, the sensitivity, specificity, positive predictive value, and negative predictive value were high, 87.5%, 76.9%, 70%, and 90.9%, respectively. Significance: This study demonstrates that hemodynamic responses related to epileptic activity can help delineate the epileptogenic region. Full concordance between maximum response and surgical resection is indicative of seizure freedom, whereas a resection leaving the maximum response intact is likely to lead to a poor outcome. EEG/fMRI is noninvasive but is limited to patients in whom interictal epileptic discharges can be recorded during the 60-90 min scan.

EEG-fMRI in the presurgical evaluation of temporal lobe epilepsy

“…This contrasts to a method we and others have used previously, in which a special emphasis was given to the BOLD cluster containing the voxel with the highest degree of statistical significance, an approach well suited, in principle, to summarise patterns can extend across multiple lobes 5 8 9. Also, in our group's previous studies, we used a type of concordance scheme that takes into account the presence of BOLD changes in the presumed (or confirmed) EZ but also in distant regions;5 8 this reflected a wish to answer broader questions related to the possible meaning of the BOLD maps associated with epileptic activity.…”

Dysfunction of Neurovascular/Metabolic Coupling in Chronic Focal Epilepsy

“…A summary of equations of the model was provided in Table I. Taking into consideration previous reports about possible dysfunctions in the hyperemic response and oxygen metabolism in epileptogenic cortices [3][4][5][6][7][8][9], parameters ε and κ are of great interest in our study. ε is an unknown parameter in the model relating neuronal activity to the CBF.…”

“…Over the last decade, EEG-fMRI technique has been progressively [3][4][5][6]. This technique offers good sensitivity (88%) and specificity (75%) in localizing epileptogenic cortices in patients with focal refractory epilepsy [7]. By using the EEG-fMRI technique, we can generate wholebrain maps of blood oxygenation level-dependent (BOLD) activations evoked by interictal epileptiform discharges (IEDs), which are useful to identify irritative zones.…”

RF Heating of Gold Cup and Conductive Plastic Electrodes during Simultaneous EEG and MRI

“…These studies include reports of high variability in the timing of hemodynamic changes relative to the timing of interictal spikes 6,7 , with the intriguing finding that, in several cases, the onset of hemodynamic changes appears to precede spike onset 8,9 . Also of note are recent findings that the concordance (or lack thereof) between the brain areas that show spike-related fMRI activation and the presumed epileptogenic zone (identified through a combination of scalp EEG, intracranial electrodes and behavioral measures) is predictive of seizure freedom following epilepsy surgery 10,11 .…”