Imaging of the epilepsies.

Imaging of epilepsy patients is challenging, since epileptogenic lesions (defined as structural lesions causally related to the epilepsy syndrome) may be small and often do not change during life. Prior clinical information about the epilepsy syndrome and the semiology of the seizures is needed in order to plan the examination properly. The effort to detect an epileptogenic lesion is directed to partial (focal) epilepsy syndromes whereas--by definition--no lesion is identified in idiopathic epilepsies. Most patients with partial epilepsies suffer from mesial temporal lobe epilepsies. In these patients, 2- to 3-mm-thick T2-weighted and fluid-attenuated inversion-recovery (FLAIR) fast spin echo slices along or perpendicular to the temporal lobe length axis have the highest diagnostic efficacy. In contrast, in patients with extratemporal lobe epilepsies perpendicular FLAIR slices through the anatomic region, from which, due to clinical and EEG criteria, the seizures are likely to originate, are preferred. The imaging features of common epileptogenic lesions (hippocampal sclerosis, long-term epilepsy-associated tumours, focal cortical dysplasias, vascular malformations, encephalitis including limbic and Rasmussen's encephalitis, gyral scarring including ulegyria) are detailed in the second section of this paper.