Insular epilepsy: similarities to temporal lobe epilepsy case report

Abstract

-Insular epilepsy has been rarely reported and its clinical and electrographic features are poorly understood. The electrographic study of the insula is difficult since it is hidden from the brain surface by the frontal and temporal lobe. A 48 years-old woman started having simple partial autonomic and complex partial seizures with automatisms and ictal left arm paresis 8 years prior to admission. Seizure's frequency was 1 per week. Pre-operative EEG showed a right temporal lobe focus. Neuropsychological testing disclosed right frontotemporal dysfunction. MRI showed a right anterior insular cavernous angioma. Intraoperative ECoG obtained after spliting of the sylvian fissure showed independent spiking from the insula and temporal lobe and insular spikes that spread to the temporal lobe. The cavernous angioma and the surrounding gliotic tissue were removed and the temporal lobe was left in place. Post-resection ECoG still disclosed independent temporal and insular spiking with a lower frequency. The patient has been seizure-free since surgery. Insular epilepsy may share many clinical and electroencephalographic features with temporal lobe epilepsy.KEY WORDS: epilepsy, insula, electrocorticography, cavernous angioma.Epilepsia insular: similaridades à epilepsia do lobo temporal -relato de caso RESUMO -A epilepsia insular tem sido raramente relatada e suas características clínicas e eletrencefalográficas são pobremente conhecidas. O estudo eletrográfico da ínsula é difícil já que ela se encontra recoberta pelos lobos frontal e temporal. Uma paciente, de 48 anos, começou a ter crises parciais simples autonômicas e crises parciais complexas com automatismos e paresia crítica de membro superior esquerdo 8 anos antes desta internação. A frequência de crises era de 1/semana . O EEG pré-operatório mostrou foco temporal direito. Testagem neuropsicológica demonstrou disfunção fronto-temporal direita. RMN demonstrou cavernoma insular anterior direito. A eletrocorticografia intraoperatória obtida após a abertura da fissura sylviana demonstrou a presença de espículas independentes na ínsula e no lobo temporal, além de descargas que se originavam na ínsula e espraiavam ao lobo temporal. O angioma cavernoso e a área gliótica ao seu redor foram removidos e o lobo temporal foi deixado em seu lugar. A eletrocorticografia após a ressecção ainda demonstrou a presença de descargas nestas regiões, em menor frequência. A paciente está sem crises desde a cirurgia. A epilepsia insular pode compartilhar diversos aspectos clínicos e eletrográficos com a epilepsia do lobo temporal. PALAVRAS-CHAVE: epilepsia, insula, eletrocorticografia, angioma cavernoso.Insular epilepsy has been rarely described in the literature. The insula is one of the five cerebral lobes and its cortex is situated deeply within each hemisphere. It is overlayed by the frontal and temporal neocortex and this explains how difficult it should be to get reliable EEG sampling

Localization of Abnormal Discharges Causing Insular Epilepsy by Magnetoencephalography

“…Scalp electroencephalography (EEG) is relatively insensitive to detect neuronal activity in the insula because of this deep location, so insular epilepsy is rarely reported (Fiol et al 1988;Cukiert et al 1998). Furthermore, the insular cortex has multiple connections with the adjacent cerebral cortex, especially with the temporal lobe (Penfield and Faulk 1955;Augustine 1996), so that insular epilepsy shares similar clinical features with temporal lobe epilepsy (TLE), including nausea, abnormal throat sensation, epigastric discomfort, chewing, and lip smacking (Fiol et al 1988;Roper et al 1993;Cukiert et al 1998;Ostrowsky et al 2000). Scalp EEG localizes the epileptic discharges of both TLE and insular epilepsy in the anterior temporal lobe.…”

“…Scalp EEG localizes the epileptic discharges of both TLE and insular epilepsy in the anterior temporal lobe. Therefore, insular epilepsy may be misdiagnosed as TLE, unless a structural lesion is identified within the insula (Roper et al 1993;Cukiert et al 1998) or epileptic discharge is detected within the insula by invasive EEG monitoring using intracranial electrodes (Roper et al 1993;Isnard et al 2000).…”

Insular epilepsy surgery under neuronavigation guidance using depth electrode

“…Because of its location deep within the sylvian fissure, scalp electroencephalography is relatively insensitive to the electrical activity within the insulae [17]. Chronic implantation of the insular with subdural electrodes requires stable placement of strip electrodes within a narrow space, which is hindered by middle cerebral branches and sylvian veins [3]. With stereotactic depth electrode insertion through the sylvian fissure, implantation must be carefully performed to protect the middle cerebral artery branches [3].…”

“…The insular cortex hidden by the frontal or temporal operculum can be an epileptic zone [3,14,15]. Seizures originating in the insular cortex used to be confused with frontal, temporal, or frontotemporal lobe seizures.…”

“…Unacceptable morbidity and mortality occur with insular cortex removal because of neurovital structures and the associated vasculature [11,18,21,22]. Because of its location deep within the sylvian fissure, scalp electroencephalography is relatively insensitive [3,24]. The implantation of subdural electrodes, such as transsylvian or stereotactic depth electrodes, perpendicular to the midsagittal plane by the transopercular route can be used for limited monitoring of the wide insular cortex [3,14].…”