The Insula and Its Epilepsies

Abstract

Insular seizures are great mimickers of seizures originating elsewhere in the brain. The insula is a highly connected brain structure. Seizures may only become clinically evident after ictal activity propagates out of the insula with semiology that reflects the propagation pattern. Insular seizures with perisylvian spread, for example, manifest first as throat constriction, followed next by perioral and hemisensory symptoms, and then by unilateral motor symptoms. On the other hand, insular seizures may spread instead to the temporal and frontal lobes and present like seizures originating from these regions. Due to the location of the insula deep in the brain, interictal and ictal scalp electroencephalogram (EEG) changes can be variable and misleading. Magnetic resonance imaging, magnetic resonance spectroscopy, magnetoencephalography, positron emission tomography, and single-photon computed tomography imaging may assist in establishing a diagnosis of insular epilepsy. Intracranial EEG recordings from within the insula, using stereo-EEG or depth electrode techniques, can prove insular seizure origin. Seizure onset, most commonly seen as low-voltage, fast gamma activity, however, can be highly localized and easily missed if the insula is only sparsely sampled. Moreover, seizure spread to the contralateral insula and other brain regions may occur rapidly. Extensive sampling of the insula with multiple electrode trajectories is necessary to avoid these pitfalls. Understanding the functional organization of the insula is helpful when interpreting the semiology produced by insular seizures. Electrical stimulation mapping around the central sulcus of the insula results in paresthesias, while stimulation of the posterior insula typically produces painful sensations. Visceral sensations are the next most common result of insular stimulation. Treatment of insular epilepsy is evolving, but poses challenges. Surgical resections of the insula are effective but risk significant morbidity if not carefully planned. Neurostimulation is an emerging option for treatment, especially for seizures with onset in the posterior insula. The close association of the insula with marked autonomic changes has led to interest in the role of the insula in sudden unexpected death in epilepsy and warrants additional study with larger patient cohorts.

Semiologic subgroups of insulo‐opercular seizures based on connectional architecture atlas

“…A variety of subjective and objective signs have been recorded through SEEG insular explorations, including viscerosensory, somatosensory, and auditory sensations; autonomic symptoms; gestural motor behaviors; and elementary motor signs 2‐6 . The diversity of insular seizures reflects distinctive propagation pathways including perisylvian, temporal, and frontal patterns 7,8 ; as such, insular seizures are great mimickers of seizures originating from elsewhere in the brain 9 . On the other hand, seizures arising from other lobes also often involve insulo‐opercular cortex, such as temporal‐plus epilepsy 10 .…”

Indications, Techniques, and Outcomes of Robot-Assisted Insular Stereo-Electro-Encephalography: A Review

“…A major breakthrough occurred in 2000, when Isnard et al using stereo-electro-encephalography (SEEG), demonstrated that some failures of temporal lobectomy could be related to seizures originating in the insular cortex ( 5 ). Since then, the role of the insula in surgically focal epilepsy has been extensively investigated ( 6 ), showing first that insular (or insulo-opercular) cortex epilepsy may mimic temporal, frontal, or parietal epilepsy, and second that the insula can be part of widely extended epileptogenic zones such as in the case of temporal “plus” epilepsies ( 7 ). Overall, the complexity of focal epilepsies involving the insula makes the precise determination of the ictal topographical culprit of paramount importance, especially when a surgical treatment is envisioned.…”

Ictal semiology, functional anatomy and multimodal diagnostic in patients with insular epilepsies

“…SEEG can detect simultaneous insular-opercular seizure onset in patients with sleep related paroxysmal motor behaviours [17]. In MRI normal cases extensive individual sampling also of extrainsular regions to which the insula is closely connected should be performed [28].…”