Guidelines for Preoperative Diagnostic Evaluation of Patients with Pharmacoresistant Epilepsy

Surgical techniques of treating patients with pharmacoresistant epilepsy have changed considerably in the last 25 years. Greatest success has been achieved in patients with magnetic resonance imaging (MRI) positive temporal lobe epilepsy (TLE), especially in patients with hippocampal sclerosis, and more recently in patients with extratemporal lesional epilepsy. This improvement is mostly due to large progress in imaging technology, but also in neurophysiological methods and microsurgical techniques. Very important is careful patient selection and preoperative evaluation via identification of the semiology of seizures, localization of epileptogemc lesion, and ictal onset zone. In preoperative evaluation of patients with pharmacoresistant epilepsy, modern diagnostic techniques can be divided into noninvasive and invasive. Noninvasive methods include: (a) video-electroencephalography (EEG) recording (interictal and ictal); (b) preoperative neuropsychological testing; (c) dedicated neuroradiological examination, i.e. 3T brain magnetic resonance imaging (MRI), with specialized M RI techniques including morphometric MR analysis, MR spectroscopy, functional MRI with MR tractography, and MR volumetry; (d) nuclear-medicine methods, i.e. single photon emission computed tomography (SPECT) and positron emission tomography (PET); and (e) magnetoencephalography (MEG). Invasive methods include: (a) Wada test (intracarotid amobarbital or etomidate testing); (b) semi-invasive video-EEG monitoring, using sphenoidal or foramen ovale electrodes; and (c) invasive video-EEG monitoring, using subdural strip and grid as well as depth electrodes. Invasive EEG monitoring, where selection of the type of intracramal electrodes and their placement depends on the localization of epileptogemc region, is used if MRI is nonlesional, if there is discrepancy between ictal or interictal EEG recordings and brain MRI, between the seizure semiology and the imaging findings, and between the seizure semiology and EEG recording. It is also used in case of dual pathology and polytope changes, when it is not known which pathomorphological lesion is epileptogenic, and in case of positive brain MRI when pathomorphological lesion is localized near motor and eloquent cortex. The possible complications include ultra-cranial hemorrhage, cortical lesions and infection.