Association of EEG-fMRI Responses and Outcome After Epilepsy Surgery

Abstract

Objective:To assess the utility of EEG-fMRI for epilepsy surgery, we evaluated surgical outcome in relation to the resection of the most significant EEG-fMRI response.Methods:Patients with post-operative neuroimaging and follow-up of at least one year were included. In EEG-fMRI responses, we defined as “primary” the cluster with the highest absolute t-value located in the cortex, and evaluated three levels of confidence for the results. The threshold for low confidence was t ≥ 3.1 (p < 0.005); the one for medium confidence corresponded to correction for multiple comparisons with a false discovery rate of 0.05; and a result reached high confidence when the primary cluster was much more significant than the next highest cluster. Concordance with the resection was determined by comparison to post-operative neuroimaging.Results:We evaluated 106 epilepsy surgeries in 84 patients. An increasing association between concordance and surgical outcome with higher levels of confidence was demonstrated. If the peak response was not resected, the surgical outcome was likely to be poor: for the high confidence level, no patient had a good outcome; for the medium and low levels, only 18% and 28% had a good outcome. The positive predictive value remained low for all confidence levels, indicating that removing the maximum cluster did not ensure seizure freedom.Conclusion:Resection of the primary EEG-fMRI cluster, especially in high confidence cases, is necessary to obtain a good outcome, but not sufficient.Classification of Evidence:This study provided Class II evidence that failure to resect the primary EEG-fMRI cluster is associated with poorer epilepsy surgery outcomes.

Not a Slam-Dunk: Assessing the Role of EEG/fMRI in the Presurgical Evaluation

“…The previous study by the same group (some of the participants of that study are likely included in the current report) included 35 patients with lesional or non-lesional epilepsy who successfully underwent EEG/fMRI and had focal fMRI activation identified (out of 47 who participated). 1 , 8 In this earlier study, the degree of concordance between the BOLD peaks and surgical outcomes was similar to the present study. The other conclusion of that study was that partial concordance or partial discordance of the EEG/fMRI results and resection site were best considered inconclusive in regards to the post-surgical outcome prediction while the highly concordant and discordant results had high value for predicting favorable or unfavorable outcomes, respectively.…”

“…While the authors clearly indicate that after division into three groups the number of participants per group was smaller, the N of 84 EEG/fMRI patients and N of 106 surgeries is very respectable. 1 This underscores the two important aspects of this line of research. One is that large numbers of participants are necessary to address the important surgical outcome questions, and the second is that it takes a very long time to collect such data by a single center (here 13 years).…”

“…Also important are meticulous data collection and handling methods and a clear description of the process that is provided in sufficient detail in the manuscript. 1 The drawback is that this multimodality technique, beyond few very limited and fortuitous studies, rarely captures ictal events and the data analyses need to rely, for the most part, on BOLD signal changes related to interictal epileptiform discharges (IEDs). This is because it would be virtually impossible (or at least impractical) to keep collecting EEG/fMRI data until a seizure had occurred because of the scanner time needed as well as because of the motion artifact generated by seizure events that would make the data useless.…”

“…One is that large numbers of participants are necessary to address the important surgical outcome questions, and the second is that it takes a very long time to collect such data by a single center (here 13 years). 1 How does this study compare to some of the other EEG/fMRI surgical outcome studies? The previous study by the same group (some of the participants of that study are likely included in the current report) included 35 patients with lesional or non-lesional epilepsy who successfully underwent EEG/fMRI and had focal fMRI activation identified (out of 47 who participated).…”

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Association of EEG-fMRI Responses and Outcome After Epilepsy Surgery 1 Andreas Koupparis, Nicolás von Ellenrieder, Hui Ming Khoo, Natalja Zazubovits, Dang Khoa Nguyen, Jeffery A Hall, Roy W R Dudley, Francois Dubeau, and Jean Gotman. Neurology 2021;97(15):10. doi: 10.1212/WNL.0000000000012660

Objective

To assess the utility of EEG-fMRI for epilepsy surgery, we evaluated surgical outcome in relation to the resection of the most significant EEG-fMRI response.

Methods

Patients with post-operative neuroimaging and follow-up of at least 1 year were included.

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