Communication du Docteur MICHEL au XXVIIIème Congrès du GRAL
Epileptic activity in the brain is increasingly considered as the dysfunction of a neuronal network of cortical and sub-cortical brain structures, rather than a single pinpoint source. The advent of structural Magnetic Resonance Imaging (MRI) has revolutionized the exploration of epilepsy. Emerging imaging data suggest that anomalies extending beyond the lesion may negatively impact outcome and challenge the conventional model of focal epilepsy and revive the concept of distributed neural networks. The corpus callosum is the main band of interhemispheric axonal fibers in the human brain. Corpus callosum agenesis has widely varying symptoms, mainly associated with epilepsy, cognitive failure, and neuropsychiatric disorders. The limbic system has always been considered as complex arrangement of transitional structures between cortical and subcortical structures. So, its involvement in white matter disease is logical. The subcortical limbic structures are amygdala, mammilkary bodies, hypothalamus, some thalamic nuclei and ventral striatum (nucleus accubens). The cortical components of the limbic system include areas of increasing complexity, separated into limbic and para-limbic zones. Functionnaly, the paralimbic areas contribute to the activity of three distinct networks: 1°) The hippocampal-diencephalic limbic circuit and the parahippocampal retrosplenial network; 2°) The temporo-amygdala-orbito-frontal network; 3°) The dorso-medial default-mode activity network. Among limbic syndromes, lesions of hippocampal-diencephalic limbic circuit and the parahippocampal retrosplenial, have been reported as responsible of epilepsy. Damage to the limbic white matter tracts, such as the fornix, the incinate fasciculus is reported in patients with unilateral temporal lobe epilepsy. This damage is diffuse and often extends controlateraly. Memory deficits are associated with epilepsy (delayed recall). In children with temporal lobe epilepsy, associate with abnormal lesions of temporal and frontal white matter we can observe mental retardation associated with epilepsy (Geschwind’s syndrome). The emergence of psychotic symptoms in temporal lobe epilepsy is associated with white matter changes of frontal lobes. The lateralization of MRI according to the epileptogenic zone enable the observation of specific abnormalities of each type of epilepsy. But the implications of white matter abnormalities observed in epileptic patients remain unknown. In approximately 20-30% of epileptic patients drug resistant, the apparent lesions responsible for epileptogenesis are not visible on conventional MRI.DTI technique enables clinicians to select ROI and correlate white matter alterations with clinical signs. It could explain the coexistence of epilepsy with behavioral disorders.