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  • The Electrocorticogram and Connectivity Dynamics Before and After Corpus Callosotomy follows Lateralization of Seizure Foci

    Final Number:

    Victor Du MD; Pierre Megevand; Erin Yeagle BS; Jose Herrero PhD; Miklos Argyelan MD; Ashesh Mehta MD, PhD

    Study Design:

    Subject Category:

    Meeting: 2016 ASSFN Biennial Meeting

    Introduction: Rapidly propagating frontal lobe seizures that are difficult to lateralize may do so after corpus callosotomy. We performed callosotomy using laser interstitial thermal therapy (LITT) in three patients who were undergoing stereoelectroencephalography (SEEG) and examined both the electrocorticogram electrophysiology and neuroimaging connectivity measures.

    Methods: SEEG electrodes were placed three patients with suspected underlying laterization. All three patients underwent anterior corpus callosotomy using stereotactic laser interstitial ablation with electrodes in place (e.g. Fig.1). Resting fMRI, diffusion tractography were obtained one week before electrode implantation and one week after. In addition, the resting electrocorticogram and corticocortical evoked potential mapping were performed before and after the callosotomy procedure using the same electrodes that were rigidly held in place with skull bolts, resulting in minimal electrode migration after callosotomy.

    Results: All patients had marked lateralization of both interictal activity (Figure 3) as well as seizure onset (Figure 4). Alterations in interhemispheric connectivity was reliably demonstrated using DTI and resting fMRI. This was paralleled by a similar changes in resting electrocorticography and corticocortical evoked potentials over areas with projections to the area of the callosum that was lesioned. Both intrahemispheric connectivity as well as interhemispheric connectivity beyond the callosotomy were relatively maintained as reflected by electrocorticographic- and MRI-based measures.

    Conclusions: Callosotomy using LITT may be used in conjunction with SEEG to accurately identify ictal onset in cases where seizure lateralization is difficult. Our results further confirm the correspondence of MRI- and electrophysiological-based connectivity measures by showing that alterations of function connectivity occur using both methods after surgical disconnection.

    Patient Care: We aim to establish functional connectivity studies such as cortico-cortical evoked potentials (CCEPs) as a useful adjunct to planning clinical interventions such as disconnection surgeries and other ablative procedures.

    Learning Objectives: To recognize the role of functional connectivity studies as a useful adjunct to anatomical connectivity studies in both normal and pathological brain states.

    References: Iwasaki, M. (2016). ‘Clinical profiles for seizure remission and developmental gains after total corpus callosotomy’, Brain and Development, vol. 38, no. 1, pp. 47-53 Yaffe, R. (2015). ‘Physiology of functional and effective networks in epilepsy’, Clinical Neurophysiology, vol. 126, no. 2, pp. 227-236 Keller C. J. (2014). 'Mapping human brain networks with cortico-cortical evoked potentials', Philosophical Transactions of the Royal Society B, 369 Keller, C. J. (2014). 'Corticocortical evoked potentials reveal projectors and integrators in human brain networks', The Journal of Neuroscience, vol. 34, no. 27, pp. 9152-9163 Enter, L. (2014). ‘Evoked effective connectivity of the human neocortex’, Human Brain Mapping, vol. 35. no. 12, pp. 5736-53

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