Abstracts

Rationale: Mesial temporal lobe epilepsy (mTLE) typically involves the amygdalo-hyppocampal system. However, quantitative techniques of neuroimaging are able to demonstrate more widespread damage. Interictal spikes identified in patients with mTLE probably arise from the mesial structures but neocortex also may play a role in the generation of the discharges. The objective of this investigation was to explore structural and neurophysiological features of the temporal neocortex in patients with mTLE using cortical thickness analysis and dipole source imaging techniques.Methods: Ten patients with mTLE with unilateral hippocampal sclerosis (HS) ipsilateral to interictal discharges were selected. MRI: All patients and a control group of 20 healthy individuals (11 women, mean age 32 7 years) were submitted to 3 Tesla MRI. Volumetric sequence was used for structural analysis. Cortical thickness analysis was performed with Freesurfer image analysis suite. Images were submitted to quality improvement, tessellation of white/gray matter boundaries, registration and reconstruction with creation of cortical thickness maps. FInally, these maps were smoothed with a 10mm FWHM filter. Statistical analysis was conducted using general linear model. Patients with right and left mTLE were grouped and compared to controls. Statistical level selected was a p < 0.05. EEG: Exams were recorded with 10-20 system of electrode placement using Nihon-Kohden system with Silverman s electrodes and with sampling rate of 1000 Hz. All patients presented at least one exam with typical temporal lobe spikes. Source localization was conducted using BESA software. Spikes were selected, centered and averaged. Equivalent dipole and CLARA algorithms were applied for source localization. Principal component analysis was used to select the onset fit interval in the ascending portion of the averaged discharge.Results: Right mTLE: 5 patients (4 women, mean age 37 12 years) and 318 discharges (63 61) investigated. Dipole source analysis showed onset of the discharges in the superior temporal gyrus in two patients, inferior frontal gyrus in two patients and insula in one patient. Discharge propagation was observed in 4 patients. Cortical thickness was reduced mainly in the middle temporal gyrus (value 4.0, size 470mm2, Tal x = 58 y = -20 z = -14, p < 0.0001). Left mTLE: 5 patients (4 women, mean age 44 9 years) and 274 discharges (54 49) investigated. Dipole source analysis showed onset of the discharges in the superior temporal gyrus in two patients and inferior frontal gyrus in three patients. Discharge propagation was observed in 3 patients. Cortical thickness was reduced in the supramarginal gyrus (value 5.3, size 360mm2, Tal x = -50 y = -45 z = -23, p < 0.00001).Conclusions: This investigation supports the importance of the neocortex in the mechanisms of temporal spikes generation. Neuroimaging and EEG source analysis showed similar findings demonstrating extra-hippocampal involvement in mTLE. It was also disclosed a different neuroanatomical involvement in patients with right or left HS.