Mapping the insula with stereo‐electroencephalography: The emergence of semiology in insula lobe seizures

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Objective

Insula epilepsy is rare and can be evaluated effectively by Stereotactic intracerebral EEG (SEEG). Many previous studies of insulo‐opercular seizures have been unable to separate insular and opercular onset. With adequate sampling of the insula, this study shows this is possible.

Methods

We analysed intra‐insular dynamics and extra‐insular propagation in twelve patients with “pure” insula epilepsy (n = 9) or insular and only deepest opercular involvement (n = 3) at seizure onset. Review of semiology defined clinical groups, agglomerative cluster and principal component analysis of semiological features was performed. Quantitative epileptogenicity, intrainsular and extrainsular propagation was computed via time frequency analysis and epileptogenicity mapping.

Results

Seizure onset patterns were heterogeneous, the seizure onset zone was focal. Seizure onset and first ictal change within insula functional subdivision correlated with aura and reflex component. No paninsular spread occurred, contralateral insular spread was very early. Whilst the discharge was intrainsular, clinical signs related to aura or vegetative signs. Extra‐insular propagation was early and related to emergence of majority of clinical signs. Cluster analysis found an anterior, intermediate and posterior insula seizure onset group. The largest principle component separated anterior insula manifestations including early hypermotor signs, early recovery and no aura from posterior insula features of early dystonia, early tonic motor features and sensorimotor aura.

Interpretation

Aura is vital to identifying seizure onset and relates to insula functional subdivision. Seizures are heterogenous, extra‐insula propagation occurs early accounting for most of the semiology. With adequate sampling ‘pure insula’ epilepsy can be identified and focal curative resection is possible.

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