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PURPOSE: Ictal single-photon emission computed tomography (SPECT) may help localize the seizure-onset zone (SOZ) by detecting changes in regional cerebral blood flow induced by epileptic discharges. This imaging method also reveals hyperperfusions in areas of seizure propagation, including the hemisphere contralateral to the SOZ. We have studied the occurrence, the topography, and the clinical value of such contralateral ictal hyperperfusion areas (HPAs). METHODS: We examined data from presurgical evaluations of 36 consecutive patients with pharmacoresistant partial epilepsy of various localizations. Ictal and interictal SPECT examinations were made with 99mTc-ECD, and the scans were processed for coregistration, normalization, subtraction, and merging with MRI images. RESULTS: Contralateral HPAs were observed in 72% of the patients: 50% of mesiotemporal epilepsy cases with hippocampal sclerosis, 85.7% of the other mesiotemporal epilepsies, 85.7% of neocortical lateral temporal epilepsies, and 87.5% of extratemporal epilepsies. Contralateral HPAs were usually symmetrical to the SOZ, forming a mirror image, observed in 57.1% of the patients. They could be slightly asymmetrical in mesiotemporal epilepsies, perhaps because of the particular anatomic pathways linking temporal lobes. In neocortical epilepsies, they were located in the cortex homotopic to the SOZ. CONCLUSIONS: We show that the symmetrical nature of the mirror image usually does not disturb SPECT interpretation. It can confirm the location of the SOZ (11 patients) and even occasionally improve the precision of its definition (nine patients) by restraining several potential SOZ-related HPAs to a single one or by permitting a restricted localization of the SOZ in a large HPA.

International audience; PURPOSE: Different lines of evidence suggest that the insular cortex has many important functional roles. Direct electrical stimulation (ES) of the human insular cortex during surgical procedures for epilepsy, functional imaging techniques, and lesion studies also occasionally induces clinical responses. METHODS: In this study, we evaluated 25 patients with drug-refractory focal epilepsy by stereotactically implanting at least one electrode into the insular cortex using an oblique approach (transfrontal or transparietal). One hundred twenty-eight insular sites (each situated between two contiguous contacts within the same electrode) were examined within the gyral substructures. We located each stimulation site by fusing preimplantation three-dimensional (3D) magnetic resonance imaging (MRI) images with the postimplantation 3D computed tomography (CT) scans that revealed the electrode contacts. RESULTS: Sixty-seven stimulations induced at least one clinical response. Stimulation from within the insular cortex evoked 83 responses, without evidence of afterdischarge in the insular or extrainsular regions. We classified the principal responses as sensory (paresthesias and localized warm sensations), motor, pain, auditory, oropharyngeal, speech disturbances (including speech arrest and reduced voice intensity) and neurovegetative phenomena, such as facial reddening, generalized sensations of warmth or cold, hypogastric sensations, anxiety attacks, respiratory accelerations, sensations of rotation, and nausea. CONCLUSIONS: These findings may indicate a functional specificity for the insular gyri and show the need for exploring this structure during invasive presurgical evaluation of epileptic patients according to seizure manifestations.

International audience; PURPOSE: The determination of epileptogenic structures in partial epilepsy is crucial in the context of epilepsy surgery. In this study we have quantified the "epileptogenicity" of mesial temporal lobe structures (M), lateral neocortical regions (L), and extratemporal perisylvian structures (ET) in patients with temporal lobe epilepsy (TLE), in order to classify the brain networks involved in seizure generation. METHODS: Thirty-four patients having TLE investigated by intracerebral recordings using stereotactic electroencephalography (EEG) (SEEG) were selected. Epileptogenicity of M, L, and ET structures was quantified according to the "epileptogenicity index" (EI), a new way to quantify rapid discharges at seizure onset, ranging from 0 (no epileptogenicity) to 1 (maximal epileptogenicity). RESULTS: Automatic clustering using EI values from M, L, and ET separated patients into four classes: mesial group (max EI in M), lateral group (max EI in L), mesiolateral group (high EI in both M and L) and temporoperisylvian group (TPS) (high values in ET). The median number of highly epileptogenic structures (defined by EI >0.3) was four, a result confirming that most TLE is organized as "epileptogenic networks." We found that the duration of epilepsy was correlated with the number of epileptogenic structures and that surgical prognosis was also related to the extent of the epileptogenicity in the brain. CONCLUSIONS: Several distinct epileptogenic networks are involved in seizure generation in TLE. Findings advocate for a progressive recruitment of epileptogenic structures in human brain with time.