Magnetic Source Imaging and Epilepsy Surgery Failure
Abstract number :
2.035
Submission category :
3. Neurophysiology / 3D. MEG
Year :
2022
Submission ID :
2204487
Source :
www.aesnet.org
Presentation date :
12/4/2022 12:00:00 PM
Published date :
Nov 22, 2022, 05:25 AM
Authors :
Victoria Ros, MD – Montreal Neurological Institute, McGill University; Aura Gonzalez, MD, EEG CNSF – Neurology – Montreal Neurological Institute, McGill University; Jawata Afnan, BSc, MSc – Biomedical Engineering – Montreal Neurological Institute, McGill University; Jeffery Hall, MD, MSc, FRCS(C) – Neurosurgery – Montreal Neurological Institue, McGill University; Giovanni Pellegrino, MD – Neurology – Montreal Neurological Institute, McGill University; Christophe Grova, PhD – Biomedical Engineering – McGill University, Concordia University; Eliane Kobayashi, MD, PhD – Epilepsy Unit, Neurology – Montreal Neurological Institute, McGill University
Rationale: Post-operative seizure freedom is still low in patients with drug-resistant epilepsy (DRE), mostly due to incomplete removal of the epileptogenic tissue. MSI of interictal epileptiform discharges (IEDs) can provide localization of the focus and of activity propagated from it, shedding light on possible focal generator manifesting with bilateral synchronous, hemispheric or widespread discharges.1 Here we aimed to review the patterns of pre-surgical MSI in patients who did not achieve seizure freedom after surgery.
Methods: This is a retrospective study from a cohort of magnetoencephalography (MEG) recorded pre-surgically, as research protocol, in DRE patients who did not achieve seizure freedom after resective surgery. The distributed source model consisted of dipolar sources on every vertex of the mesh obtained from each patient’s MRI, oriented perpendicularly to the cortical surface. We applied the coherent maximum entropy on the mean (cMEM), a nonlinear probabilistic approach relying on maximizing relative entropy, as inverse solution.2,3 For each patient, similar IEDs were averaged and generated one MSI map, for which we qualitatively evaluated spatial concordance of sources with the surgical cavity from post-surgical MRI.
Results: Twelve patients were included. Six patients underwent one surgery, and 6 patients were reoperated. A single source in MSI was found in 2/12 patients, whereas more than one source was identified in 10/12 patients. In 7/12 patients, MSI showed multifocal/bilateral sources, in 3/12 patients a focal source was found but the remaining investigations indicated a widespread epileptogenicity and in 2/12 patients there was a focal source which was however not fully resected. The primary source was fully resected in only 3/12 patients (first surgery=1, reoperation=2). Resection(s) included the primary source in 6/12, the secondary but not the primary source in 1/12 and neither primary nor secondary in 5/12 patients._x000D_
Conclusions: MSI may identify a focal source in patients with otherwise evidence of a more widespread or multifocal epileptogenicity from pre-surgical workup. In these patients, resection of focal sources even when complete, does not render the patient seizure-free. Clinical indication and yield for MEG and MSI in multifocal/widespread epilepsy remains unclear, in keeping with current guidelines. When unraveled, MSI focalities in the presence of widespread epileptogenicity should be regarded with caution in the decision-making process towards resective surgery.
References:
1. Abdallah et al (2022). Clinical Yield of Electromagnetic Source Imaging and Hemodynamic Responses in Epilepsy: Validation With Intracerebral Data. Neurology.
2. Amblard C et al (2004). Biomagnetic source detection by maximum entropy and graphical models. IEEE Trans Biomed Eng.
3. Chowdhury et al (2013). MEG source localization of spatially extended generators of epileptic activity: comparing entropic and hierarchical bayesian approaches. PLoS One.
Funding: The project that gave rise to these results received the support of a fellowship from ”La Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/AA20/11820028.
Neurophysiology