Extratemporal epilepsies mimicking temporal mesial epilepsy

Abstract

Among patients with focal seizures of mesial temporal semiology, approximately 30 % experience persistent seizures after anterior temporal resections. The causes are multiple, including unrecognized extratemporal seizure onset. We report six patients from three tertiary care centres for drug-resistant epilepsy whose clinical semiology was mesial temporal but who were found to have an extratemporal seizure onset confirmed by stereoelectroencephalography (SEEG). Three patients were non-lesional, and three had mesial parietal lesions. In three patients (two lesional, one non-lesional), the conclusion of the non-invasive data was mesial parietal epilepsy, based on video-electroencephalograms (EEG) in two patients and a positron emission tomography (PET)-scan in one patient. In two non-lesional patients, the combined non-invasive data led to the hypothesis of temporal epilepsy. In the sixth patient, the main hypothesis was left temporal epilepsy, based on the video-EEG and PET-scan, despite a probable mesial parietal focal cortical dysplasia. SEEG finally led to the diagnosis of mesial parietal epilepsy in five patients and fronto-polar in the sixth. The mechanism of rapid temporal involvement is certainly not unique. Careful analysis of non-invasive data can correct a misdiagnosis of mesial temporal epilepsy but may not be able to do so in our cases, as in the literature. The systematic use of mesial parietal and mesial frontal electrodes, notably cingulate, in the investigation of non-lesional temporal lobe epilepsy with SEEG should be implemented in a prospective study.

Keywords: Adults; Children; Epilepsy surgery; Posterior cingulum; Stereoelectroencephalography.