Association of EEG-fMRI Responses and Outcome After Epilepsy Surgery.

Koupparis, Andreas; von Ellenrieder, Nicolás; Khoo, Hui Ming; Zazubovits, Natalja; Nguyen, Dang Khoa; Hall, Jeffery A; Dudley, Roy W R; Dubeau, Francois; Gotman, Jean

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.