Insular Epilepsy: Semiology and Noninvasive Investigations

Abstract

In this review, authors discuss the semiology and noninvasive investigations of insular epilepsy, an underrecognized type of epilepsy, which may mimic other focal epilepsies. In line with the various functions of the insula and its widespread network of connections, insular epilepsy may feature a variety of early ictal manifestations from somatosensory, visceral, olfactory, gustatory, or vestibular manifestations. Depending on propagation pathways, insular seizures may also include altered consciousness, dystonic posturing, complex motor behaviors, and even autonomic features. Considering the variability in seizure semiology, recognition of insular epilepsy may be challenging and confirmation by noninvasive tests is warranted although few studies have assessed their value. Detection of an insular lesion on MRI greatly facilitates the diagnosis. Scalp EEG findings in frontocentral and/or temporal derivations will generally allow lateralization of the seizure focus. Ictal single-photon computed tomography has moderate sensitivity, whereas positron emission tomography has lower sensitivity. Among newer techniques, magnetoencephalography is highly beneficial, whereas proton magnetic resonance spectroscopy currently has limited value.

Pilot Study of Voxel-Based Morphometric MRI Post-processing in Patients With Non-lesional Operculoinsular Epilepsy

“…Because of the wealth of insular connections to surrounding lobes, the clinical manifestations of operculoinsular seizures are diverse (7,28). Therefore, the localization of the seizure onset zone in some cases can be quite difficult and this is also a major reason of some surgery failures (29)(30)(31).…”

“…Although operculoinsular epilepsy is relatively rare, it accounts for a non-negligible proportion of drug-resistant epilepsy surgical candidates and sometimes it can be difficult to be recognized (4)(5)(6). Because of the complex physiology and the rich connections to surrounding and remote structures, the clinical manifestations of operculoinsular seizures can be diverse (7). It is reported that operculoinsular epilepsy can have semiology similar to temporal lobe seizures, frontal lobe seizures or parietal lobe seizures (8)(9)(10)(11)(12)(13).…”

The Insula and Its Epilepsies

“…Genetic defects have been reported in operculo-insular epilepsy cases, including mutations in the CHRNB2 and CHRNA4 genes in 2 patients with sleep-related hypermotor seizures (functional testing under way). 24 A subtle insular focal cortical dysplasia was reported in a patient with familial focal epilepsy associated with DEPDC5 mutation. 25 Finally, Nguyen and colleagues 26 described an epileptogenic network involving the temporo-insular region in a family with reflex bathing epilepsy associated with a Q555X mutation of synapsin 1 on chromosome Xp11-q21.…”

Cortical thickness analysis in operculo-insular epilepsy

“…The wide spectrum of insular connectivity-related functions accounts for the diverse ictal manifestations observed in operculo-insular epilepsy (OIE). Insular seizures may present with various seizure manifestations including visceral, affective, autonomic and sensory auras, motor and non-motor seizure types that can mimic parietal, frontal or temporal lobe seizures and render the clinical recognition of OIE arduous ( Nguyen et al, 2009 ; Obaid et al, 2017 ). Moreover, non-invasive electrophysiological and imaging investigations including scalp electroencephalography (sEEG), ictal single-photon emission computed tomography (SPECT), positron emission tomography (PET) often fail to reveal the precise epileptic origin, eventually requiring invasive EEG monitoring to confirm the location of the epileptic focus ( Gras-Combe et al, 2016 ; Isnard et al, 2000 ; Mohamed et al, 2013 ; Ostrowsky et al, 2000 ; Ryvlin et al, 2006 ; Weil et al, 2016 ).…”

“…For those reasons, OIE remains a diagnostic challenge and probably under-recognized condition. In patients with drug-resistant OIE epilepsy, accurate identification may lead to successful epilepsy surgery while failure to recognize it may lead to resection of the wrong area and poor post-operative seizure outcome( Nguyen et al, 2009 ; Obaid et al, 2017 ; Surbeck et al, 2010 ; Alomar et al, 2017 ; Bouthillier and Nguyen, 2017 ; Freri et al, 2017 ; Malak et al, 2009 ).…”