Morphological imaging of the hippocampus in epilepsy

The hippocampus is a structure frequently involved in epilepsy, especially in partial drug-resistant forms. In addition, some hippocampal pathologies are associated with specific types of epilepsy presenting specific clinical courses and requiring specific treatments. Considering these major implications for treatment, morphological investigations of the hippocampus are crucial for epileptic patients. Indeed, discovery of hippocampal sclerosis may (depending on the clinical and electrophysiological findings) lead to the diagnosis of mesial temporal lobe epilepsy (MTLE). If the diagnosis of MTLE is retained in a case of drug-resistance, surgery may be proposed without invasive phase II investigations such as stereoelectroencephalograpy. In other instances, hippocampal abnormalities may be associated with epilepsy, but without the same value for localizing the ictal onset zone. Hippocampal dysgenesis is a strong argument for non-temporo-mesial ictal onset ipsilateral to the malformation. We describe here the specific MRI modalities adapted for hippocampal investigations and the radiological signs of hippocampal pathologies associated with epilepsy (especially hippocampal sclerosis and hippocamal dysgenesis). Hippocampus morphological investigations in epilepsy require specific MRI modalities and appropriate knowledge of the specific signs of each pathology. Careful analysis is crucial since the results may have a major impact on the therapeutic management of epileptic patients.