Insular Cortex Epilepsy: Exploring the Treasure Island of Reil

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Excerpt

The role of the insular cortex in partial epilepsy was largely neglected until very recently. Even nowadays, the insula is barely mentioned in major epilepsy textbooks. I came upon the insula years ago while browsing the literature to understand what could possibly explain the peculiar but terrifying sensation of choking experienced by one of my patients during her seizures. Increasingly aware of the various faces of insular seizures, we and other centers eventually broadened our indications for insular cortex sampling with intracerebral electrodes. To the untrained eye, insular seizures might be easily mistaken for seizures originating from other lobes; however, with accumulating data and experience, we and others came to recognize that insular seizures also have their own specificities and form a distinct type of epilepsy.
The present topical issue aims to provide a comprehensive overview of the current knowledge on insular epilepsy. The insula remains little known in comparison to the other brain lobes, but it has emerged as a very “hot” topic in neuroscience over the past years, thanks to the advances in neuroimaging. In the first article of this topical issue, the structure, connectivity, and functions of the insula are reviewed by Uddin et al. These anatomic and functional notions will greatly help understand subsequent articles. Then, Mazzola, Mauguière, and Isnard will share their 18-year experience with the electrical stimulation of the insula. Understanding the type of responses is the first step in understanding the earliest symptoms of insular seizures, whereas knowing their topography helps focus localization.
Although some patients have seizures confined to the insula or with limited extension to one or more opercula (operculo-insular epilepsy), others have “temporal plus epilepsy” with a primary temporal epileptogenic zone extending to the neighboring regions such as the insula (temporo-insular or temporo-perisylvian subgroup), the orbito-frontal cortex (temporo-orbito-frontal subgroup), and the temporo-parieto-occipital junction (temporal–parietal–occipital subgroup). Obaid et al will review the semiology of operculo-insular epilepsy and the value of noninvasive tests to recognize it, whereas Barba et al will have the hard task of discussing temporo-insular/perisylvian epilepsy, the most common type of temporal plus epilepsy. Although noninvasive tests may sometimes provide enough evidence for direct surgery, invasive EEG is still often required to confirm insular seizures, especially in nonlesional cases. Ryvlin and Picard will guide us through this process. Identifying an insular focus would be useless if one cannot intervene in that particular area to stop seizures. Hence, in the last segment of the issue, Von Lehe and Parpaley will discuss considerations for neurosurgery of the insula.
Over the last century, research on temporal lobe epilepsy has translated to significant scientific and clinical advances, from the understanding of the normal structure and function of the temporal lobe, the pathophysiological basis of temporal lobe epilepsy to methods for imaging temporal lobe pathology and strategies for managing patients with temporal lobe epilepsy. The time has come to shed light on insular epilepsy. I hope that with the present topical issue, clinicians will be better equipped to consider, recognize, and treat insular seizures in patients suffering from this long-neglected type of epilepsy. By improving the detection of insular epilepsy and increasing its understanding, better epilepsy surgery outcomes will be achieved.

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