1H-MRS Imaging in Patients with Non-Lesional Insular Cortex Epilepsy Characterized by Depth Electrode Recordings (P01.058)

Abstract

Objective: Identifying insular metabolic abnormalities using proton magnetic resonance spectroscopy imaging (1H-MRSI) during the presurgical evaluation of non-lesional insular cortex epilepsy (ICE). Background Seizures arising from the insular cortex can generate a wide variety of ictal symptoms potentially leading to a false diagnosis of temporal, frontal or parietal lobe epilepsy. In non-lesional ICE, standard non-invasive investigations such as video-EEG, SPECT and PET are often non-localizing or false-localizing potentially leading to inaccurate localization of the epileptogenic zone. Design/Methods: Using voxel-based 1H-MRSI, we studied 16 patients with suspected non-lesional ICE, 13 of which subsequently underwent insular and peri-insular depth electrode recordings, as well as 16 age-matched controls. Four voxels (8 ml each) were positioned to include bilateral anterior and posterior insular regions. Spectral analysis was performed to quantitate N-acetylaspartate (NAA) and creatinine (Cr). Comparisons of the NAA/Cr ratios between the normal and affected insula and between patients and controls were made using a one-way ANOVA. An asymmetry index (AI) was also calculated to evaluate intra-individual metabolic variations. Results: Insular interictal spikes (IIS) were recorded in 12 of 13 patients on intracerebral EEG recordings. Insular seizures were recorded in 6 of those patients (ICE). Ipsilateral and contralateral NAA/Cr ratios were found to be similar in all the groups. No difference in NAA/Cr ratios was found between ICE patients, IIS patients and healthy controls (2.05 ± 0.20, 2.16 ± 0.21 and 2.01 ± 0.16 respectively, P=0.06). Mean AIs in ICE and IIS patients were non-significant when compared to controls (P=0.17). Lateralization of the AI to the epileptic insular cortex was found in only one of 1 of 6 (17%) ICE patients. Conclusions: 1H-MRSI failed to identify significant metabolic abnormalities in patients with insular spikes and/or seizures and is hence unlikely to be useful during the presurgical evaluation of suspected ICE. Supported by: Quebec Bio-Imaging Network (QBIN) and the Savoy Foundation. Disclosure: Dr. Gibbs has nothing to disclose. Dr. Boulanger has nothing to disclose. Dr. Gilbert has nothing to disclose. Dr. Leroux has nothing to disclose. Dr. Bouthillier has nothing to disclose. Dr. Nguyen has nothing to disclose.