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  • Functional Network Analysis in Surgical Epilepsy Patients Using Magnetoencephalography

    Final Number:

    Dario J. Englot MD, PhD; Robert C. Knowlton MD; Edward F. Chang MD; Heidi E. Kirsch; Srikantan S. Nagarajan Ph.D.

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2015 Annual Meeting

    Introduction: Intractable focal epilepsy is a devastating disorder with profound effects on cognition and quality of life. Epilepsy surgery can lead to seizure freedom in patients with focal epilepsy, however, sometimes it fails due to an incomplete delineation of the epileptogenic zone (EZ). Brain networks in epilepsy can be studied with resting-state functional connectivity (RSFC) analysis, yet previous investigations using functional MRI or electrocorticography have produced inconsistent results. Magnetoencephalography (MEG) allows noninvasive whole-brain recordings, and can be used to study both long-range network disturbances in focal epilepsy and regional connectivity at the EZ.

    Methods: In MEG recordings from presurgical epilepsy patients, we examined: i) global functional connectivity maps in patients vs. controls, and ii) regional functional connectivity maps at the region of resection, compared to the homotopic non-epileptogenic region in the contralateral hemisphere.

    Results: Sixty-one patients were studied, including 30 with mesial temporal lobe epilepsy and 31 with focal neocortical epilepsy. Compared to a group of 31 controls, epilepsy patients had decreased RSFC in widespread regions, including peri-sylvian, posterior temporo-parietal, and orbitofrontal cortices (p < 0.01, FDR-corrected). Decreased mean global connectivity was related to longer duration of epilepsy and higher frequency of consciousness-impairing seizures (p < 0.01, linear regression). Furthermore, patients with increased regional connectivity within the resection site (n = 24) were more likely to achieve seizure post-operative seizure freedom (87.5% with Engel I outcome) than those with neutral (n = 15, 64.3% seizure free) or decreased (n = 23, 47.8% seizure free) regional connectivity (p < 0.02, chi-square).

    Conclusions: Widespread global decreases in functional connectivity are observed in patients with focal epilepsy, and may reflect deleterious long-term effects of recurrent seizures. Furthermore, enhanced regional functional connectivity at the area of resection may help predict seizure outcome and aid surgical planning.

    Patient Care: Functional connectivity analysis in focal epilepsy patients may lead to a better understanding of brain network dysfunction in this disorder, and help guide surgical planning and outcome prediction.

    Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe global alterations in functional connectivity in surgical epilepsy patients, and relate these disturbances to severity of illness, and 2) Understand how focal patterns of functional connectivity at the epileptogenic zone relate to post-operative seizure outcome.


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