Abstracts

Rationale: Magnetic source imaging (MSI) with magnetoencephalography (MEG) is used in epilepsy presurgical work-up to aid in the identification of epileptogenic cortex and its extent (1,2). MEG has been specifically useful in the diagnosis of insular epilepsies which are notorious for imitation of frontal, temporal, parietal lobe epilepsies due to reciprocal connections in the orbitofrontal, anterior cingulate, supplementary motor areas, parietal and temporal cortices (3). However, the relatively recent adoption of MEG in the clinical workflow has also led to some clinical equipoise regarding the significance of the presence of regional MEG spikes and benign variants. Current MEG practice to localize epileptic spikes recommends reporting on sources generating at least 5 spikes (4). A common representation of spikes is utilizing spike dipole clusters (DC) demonstrating the extent of MEG dipoles in any given region of the brain. However, the significance of MEG DC in locations other than a primary regionalized DC has not been fully established. In this setting, understanding the importance of MEG DC in the insular region for epilepsies otherwise presumed to be localized to the non-insular cortex has not been previously reported. We identify patients with MEG based insular involvement in refractory epilepsy and describe their clinical and MSI characteristics. Methods: The database for magnetic source imaging (MSI) studies for patients with refractory focal epilepsy completed at Baylor College of Medicine affiliated St. Luke’s Hospital and Texas Children’s Hospital from 2015-2018, was retrospectively evaluated. All patients with MEG insular DC, including a subset of patients who underwent subsequent epilepsy surgery with a minimum follow up of 6 months were evaluated. Data obtained included age, sex, seizure semiology, age of seizure onset, seizure frequency, magnetic resonance imaging (MRI) brain, electroencephalogram (EEG) and MEG findings (primary vs secondary cluster), surgical approach- (stereotactic EEG (SEEG)/ subdural grids), inclusion of insular coverage and presence of insular spikes on intracranial EEG (ictal and interictal), region of resection/laser ablation and seizure frequency post-operatively. Results: A total of 36 out of the 319 (11.28 %) patients had MEG DC localized to the insula (among other regions). Nineteen (52.77%) patients had primary insular DC and 17 (47.22%) had secondary insular DC. Twenty (55.55%) were adults and 16 (44.44%) were children (age18). Mean age was 2213.44 years with 17 (47.22%) females and 19 (52.77%) males. Twenty-four (66.66%) patients had some form of surgical intervention, while twelve (33.33%) were in the pre-surgical evaluation phase at the time of this review. Sixteen patients had intracranial epilepsy surgical evaluation (14 SEEG and 2 subdural grids). Out of the 14 SEEG, 11 had targeted insular coverage while 3 did not. Ten (90.90%) of the 11 patients with insular coverage by SEEG electrodes had interictal insular spikes during intracranial electrocorticography monitoring (4/11 had primary insular MEG DC, 6/11 had secondary insular MEG DC). In five (45.45%) of these 11 patients, the insula was identified to be part of the ictal onset zone based on intracranial EEG data (2/5 had primary MEG DC and 3/5 had secondary MEG DC). Tables 1 and 2. describes Engel class seizure outcomes among patients who underwent any form of therapeutic surgical intervention. Conclusions: Targeted intracranial evaluation of the insula with SEEG should be strongly considered in patients identified to have insular involvement (including primary and secondary DC) on MEG to further establish and better understand the role of insula in the primary or secondary epileptogenic networks in each individual patient. The presence of insular MEG DC (primary or secondary) may not definitively imply a primary insular onset epilepsy but may reflect the extent of epileptogenicity within the ictal network. Funding: No funding