Insular Lobe Epilepsy

Abstract

The insula, located deep within the Sylvian fissure, had long been inaccessible to the direct exploration of its functional roles and ictal involvement. During the era of intra-operative electrocorticography in the 1950s, Penfield and pioneering neurosurgeons identified residual spikes within the insula following temporal lobectomy and visceral as well as somatosensory symptoms upon direct electrical stimulation. However, it was not until the advent of modern stereo-electroencephalography (SEEG) technique that the intracranial electrodes could be safely and chronically implanted within the insula, thereby enabling anatomo-electro-clinical correlations during insular seizures. Since the first report of SEEG-recorded insular seizures in the late 1990s, the semiological knowledge of insular lobe epilepsy (ILE) has rapidly expanded. ILE has diverse clinical presentations due to the multifaceted functions of the insula and its rich anatomo-functional connections. They include somatosensory symptoms involving a large/bilateral cutaneous territory and/or taking on thermal/painful character, cervico-laryngeal discomfort ranging from slight dyspnea to laryngeal constriction, epigastric discomfort/nausea, hypersalivation, auditory, vestibular, gustatory, and aphasic symptoms. Importantly, these symptoms are mostly subjective and often masked by more overt symptoms of extra-insular seizure propagation, such as hyperkinetic behaviors due to frontal propagation. Therefore, a possible insular origin of seizures should be considered in non-lesional frontal/temporal/parietal epilepsies.