Magnetic resonance imaging and epilepsy: neurosurgical decision making.

Advances in magnetic resonance imaging (MRI) techniques have had an important impact on the decision-making process leading to surgical resection for chronic seizures. The MRI is now obtained relatively early in the work-up, and, when it shows abnormality, it assumes a crucial role in the detection of specific surgically remediable syndromes. These syndromes, when diagnosed by MR and other confirmatory studies such as electroencephalography (EEG), positron emission tomography (PET), magnetoencephalography (MEG), and neuropsychological testing, define the essential part of the surgical plan; that is, removal of the disease substrate. The availability of a host of MR techniques enable us to investigate epilepsy not only as a structural pathology but as physiological pathology reflected in abnormal blood flow, metabolism, and synaptic transmission. The mainstay of surgical treatment is the removal of the anatomic pathology, but other MR techniques may be helpful in the delineation of dual pathology in lesional cases, in appreciation of the full extent of microscopic pathology in developmental lesions, and in the imposition of restrictions on the resection based upon functional mapping. Finally, functional and anatomic maps obtained preoperatively can be related directly to the spatial coordinates of the exposed brain in the operating room using MRI-based frameless stereotactic methods. The final outcome, then, is the removal of the disease substrate without injury to adjacent, functionally salient cortical regions.