Advances in neuroimaging: management of partial epileptic syndromes

Structural and functional neuroimaging studies are essential in the evaluation of individuals with partial epilepsy syndromes. Magnetic resonance imaging (MRI) is important to delineate structural abnormalities underlying seizure disorders, commonly including hippocampal sclerosis or cortical dysplasias. Identification of a structural lesion is often a reliable indicator of the site of seizure onset. Magnetic resonance spectroscopy (MRS) allows us to investigate cerebral metabolites and some neurotransmitters. Reduction in various metabolite concentrations has proven to be prognostically valuable when no structural abnormality is identified. Positron emission tomography (PET) using deoxyglucose demonstrates areas of reduced glucose metabolism, which are the hallmark of epileptogenic zones and usually extend beyond the underlying anatomical region. It is useful in temporal lobe epilepsy for lateralization; however, results in extratemporal lobe epilepsy have been less favorable. More promising is the use of benzodiazepine receptor ligands, which are reduced in the epileptogenic zone in a more restricted distribution. This appears to be helpful in the localization of extratemporal seizure foci. Peri-ictal single photon emission computed tomography measures increased blood flow during the ictal event and is beneficial in patients with normal MRI studies to determine lateralization and localization of the ictal onset zone. All imaging modalities should be correlated with clinical and neurophysiological data.