Evaluations for epilepsy surgery

Abstract

Methods of preoperative and perioperative evaluation for surgical treatment of intractable epilepsy are described. History taking is the first important approach to recognize characteristics of each patient's epilepsy. In cases with mesial temporal lobe epilepsy, patients have not infrequently the past history of complicated febrile convulsion in infancy. To diagnose as epilepsy, it is necessary to evaluate neurophysiological testings, i.e. electroencephalogram (EEG) and magneto-encephalogram (MEG) before undertaken neuroradiological imaging. Among non-invasive diagnostic methods, EEG-video monitoring is the most fundamental. We can capture ictal EEG recordings and clinical seizure symptomatology as well as interictal epileptiform discharges in daytime and at night. It is useful to know pathognomonic clinical seizures and lateralizing signs (i.e. gelastic seizures, ipsilateral automatism and contralateral dystonic posturing, etc). The dipole tracing method is useful for identification of epileptic foci from interictal spikes. Neuroradiological examinations are necessary to detect epileptic lesions or foci after combination of CT, MRI, MR spectroscopy, PET, ictal and interictal SPECT, and near infrared spectroscopy etc. Volumetry by MR in the amygdala and hippocampus is also useful for the differential diagnosis of mesial from lateral temporal lobe epilepsy and generalized epilepsy. When preoperative workups are discordant, or MRI reveals no organic lesions, intracranial recording is necessary to recognize accurate epileptogenic areas. Electrical cortical stimulation is used to identify eloquent areas associated with individual variations to avoid postsurgical complications. When we can detect epileptic foci and recognize brain functions within and around foci, and remove all of the foci, patients can be seizure-free after resective surgery.