Chifaou Abdallah1,2, Tanguy Hedrich3,4, Andreas Koupparis2, Jawata Afnan3,2, Jeffrey Alan Hall2, Jean Gotman2, Francois Dubeau2, Nicolas von Ellenrieder2, Birgit Frauscher2,4, Eliane Kobayashi2, Christophe Grova3,2,5. 1. Multimodal Functional Imaging Lab, Biomedical Engineering Dpt, McGill University, Montreal, Canada chifaou.abdallah@mcgill.ca. 2. Montreal Neurological Institute and Hospital, Neurology and Neurosurgery Dpt, McGill University, Montreal, Canada. 3. Multimodal Functional Imaging Lab, Biomedical Engineering Dpt, McGill University, Montreal, Canada. 4. Analytical Neurophysiology Lab, McGill University, Montreal, Canada. 5. Multimodal Functional Imaging Lab, PERFORM Centre, Department of Physics, Concordia University, Montreal, Canada.
Abstract
OBJECTIVES: Accurate delineation of the seizure-onset zone (SOZ) in focal drug-resistant epilepsy often requires stereo-electroencephalography (SEEG) recordings. We aimed at: (1) proposing a truly objective and quantitative comparison between electro-encephalography/magnetoencephalography (EEG/MEG) source-imaging (EMSI), EEG/functional MRI (EEG/fMRI) responses for similar spikes with primary-irritative zone (PIZ) and SOZ defined by SEEG and (2) evaluating the value of EMSI and EEG/fMRI to predict postsurgical outcome. METHODS: We identified patients with drug-resistant epilepsy who underwent EEG/MEG, EEG/fMRI, and subsequent SEEG at the Epilepsy Service from the Montreal Neurological Institute and Hospital. We quantified multimodal concordance within the SEEG channel-space, as spatial overlap with PIZ/SOZ and distances to the Spike-onset, Spike-maximum-amplitude and Seizure-core intracerebral channels, by applying a new methodology consisting of converting EMSI results into SEEG electrical potentials (EMSIe-SEEG) and projecting the most significant fMRI response on the SEEG channels (fMRIp-SEEG). Spatial overlaps with PIZ/SOZ (AUCPIZ, AUCSOZ) were assessed by using the area under the receiver operating characteristic curve (AUC). Here, AUC represents the probability that a randomly picked active contact exhibited higher amplitude when located inside the spatial reference than outside. RESULTS: Seventeen patients were included. Mean spatial overlaps with the primary-irritative zone and seizure-onset zone were 0.71 and 0.65 for EMSIe-SEEG, and 0.57 and 0.62 for fMRIp-SEEG. Good EMSIe-SEEG spatial overlap with the primary-irritative zone was associated with smaller distance from the maximum EMSIe-SEEG contact to the Spike-maximum-amplitude channel (median distance 14 mm). Conversely, good fMRIp-SEEG spatial overlap with the seizure-onset zone was associated with smaller distances from the maximum fMRIp-SEEG contact to the Spike-onset and Seizure-core channels (median distances 10 mm and 5mm respectively). Surgical outcomes were correctly predicted by EEG/MEG in 12/15 (80%) patients and EEG/fMRI in 6/11(54%) patients. CONCLUSIONS: Using a unique quantitative approach estimating EMSI and fMRI results in the reference SEEG channel-space, EEG/MEG and EEG/fMRI accurately localized the seizure-onset zone as well as the primary-irritative zone. Precisely, EEG/MEG more accurately localized the primary-irritative zone, whereas EEG/fMRI was more sensitive to the seizure-onset zone. Both neuro-imaging techniques provide complementary localization that can help guiding SEEG implantation and selecting good candidates for surgery.
OBJECTIVES: Accurate delineation of the seizure-onset zone (SOZ) in focal drug-resistant epilepsy often requires stereo-electroencephalography (SEEG) recordings. We aimed at: (1) proposing a truly objective and quantitative comparison between electro-encephalography/magnetoencephalography (EEG/MEG) source-imaging (EMSI), EEG/functional MRI (EEG/fMRI) responses for similar spikes with primary-irritative zone (PIZ) and SOZ defined by SEEG and (2) evaluating the value of EMSI and EEG/fMRI to predict postsurgical outcome. METHODS: We identified patients with drug-resistant epilepsy who underwent EEG/MEG, EEG/fMRI, and subsequent SEEG at the Epilepsy Service from the Montreal Neurological Institute and Hospital. We quantified multimodal concordance within the SEEG channel-space, as spatial overlap with PIZ/SOZ and distances to the Spike-onset, Spike-maximum-amplitude and Seizure-core intracerebral channels, by applying a new methodology consisting of converting EMSI results into SEEG electrical potentials (EMSIe-SEEG) and projecting the most significant fMRI response on the SEEG channels (fMRIp-SEEG). Spatial overlaps with PIZ/SOZ (AUCPIZ, AUCSOZ) were assessed by using the area under the receiver operating characteristic curve (AUC). Here, AUC represents the probability that a randomly picked active contact exhibited higher amplitude when located inside the spatial reference than outside. RESULTS: Seventeen patients were included. Mean spatial overlaps with the primary-irritative zone and seizure-onset zone were 0.71 and 0.65 for EMSIe-SEEG, and 0.57 and 0.62 for fMRIp-SEEG. Good EMSIe-SEEG spatial overlap with the primary-irritative zone was associated with smaller distance from the maximum EMSIe-SEEG contact to the Spike-maximum-amplitude channel (median distance 14 mm). Conversely, good fMRIp-SEEG spatial overlap with the seizure-onset zone was associated with smaller distances from the maximum fMRIp-SEEG contact to the Spike-onset and Seizure-core channels (median distances 10 mm and 5mm respectively). Surgical outcomes were correctly predicted by EEG/MEG in 12/15 (80%) patients and EEG/fMRI in 6/11(54%) patients. CONCLUSIONS: Using a unique quantitative approach estimating EMSI and fMRI results in the reference SEEG channel-space, EEG/MEG and EEG/fMRI accurately localized the seizure-onset zone as well as the primary-irritative zone. Precisely, EEG/MEG more accurately localized the primary-irritative zone, whereas EEG/fMRI was more sensitive to the seizure-onset zone. Both neuro-imaging techniques provide complementary localization that can help guiding SEEG implantation and selecting good candidates for surgery.
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