Surgical and Post-surgical Evaluation of Epilepsy.

In drug-resistant epilepsy (DRE) patients, the aim of epilepsy surgery is to remove or disconnect the epileptogenic zone (EZ) without producing additional neurological or cognitive deficits. An extensive pre-surgical investigation is needed in order to identify and delineate the extension of the EZ, which is defined as “the site of the beginning of the epileptic seizures and of their primary organisation.” In this setting, clinical neuroradiology plays a crucial role in establishing diagnoses and selecting patients for surgery. Surgical outcome is better if a structural lesion is identified by magnetic resonance imaging (MRI) that is the radiological technique of choice for pre-surgical assessment. When MRI shows lesions that are accessible and congruent with the noninvasive electroclinical data, patients (particularly children) should be considered for surgery early on. When MRI does not identify a lesion, or the lesion is ill-defined or located close to eloquent brain areas, a more extensive pre-surgical evaluation is needed, which may involve computational analysis of MRI data, invasive electroencephalography, such as stereo-electroencephalography (SEEG), and functional imaging. Ictal SPECT, postictal perfusion MRI, and simultaneous EEG-fMRI can assist in the identification of the EZ. Interictal 18F-FDG PET or perfusion MRI shows the functional deficit zone. Eloquent brain areas are visualized by task-related fMRI and white matter bundles by diffusion tractography (DTI). Multimodal integration of structural and functional imaging is used to build up the complete surgical scene. MRI is performed in post-surgical follow-up to evaluate the completeness of the resection and to monitor potentially growing lesions, while fMRI and diffusion tractography are used to monitor patients with post-surgical deficits.