Advances of Intracranial Electroencephalography in Localizing the Epileptogenic Zone

Intracranial electroencephalography（i EEG）provides the best precision in estimating the location and boundary of an epileptogenic zone. Analysis of i EEG in the routine EEG frequency range（0.5-70 Hz） remains the basis in clinical practice. Low-voltage fast activity is the most commonly reported ictal onset pattern in neocortical epilepsy, and low-frequency high-amplitude repetitive spiking is the most commonly reported ictal onset pattern in mesial temporal lobe epilepsy. Recent studies using wideband EEG recording have demonstrated that examining higher（80-1000 Hz） and lower（0.016-0.5 Hz） EEG frequencies can provide additional diagnostic information and help to improve the surgical outcome. In addition,novel computational techniques of i EEG signal analysis have provided new insights into the epileptic network.Here, we review some of these recent advances. Although these sophisticated and advanced techniques of i EEG analysis show promise in localizing the epileptogenic zone,their utility needs to be further validated in larger studies.

Intracranial electroencephalography study in epileptic patients with dual pathology

Acommon dual pathology observed on presurgical magnetic resonance imaging （MRI） of epilepticpatients is extrahippocampal lesions combined with mesial temporal sclerosis. The hippocampus was highly vulnerable to many types of insults. However, it is difficult to detect subtle hippocampal atrophy in some patients. The most reliable method to confirm epileptogenicity is chronic intracranial electroencephalography （EEG） monitoring. In this study, we recorded intracranial EEG signals in 11 patients with dual pathology.METHODS Patient enrollment We evaluated ! 1 patients with a confirmed diagnosis of dual pathology in Yuquan Hospital, China between 2007 and 2010. The patients were satisfied with the following criteria： （1） MRI showed structural lesions in the extrahippocampal lobe; （2） a postoperative follow-up period lasting at least 24 months. For all 11 patients, both seizure frequency and impact on quality of life were judged as severe enough to justify presurgical evaluation using implanted electrodes. Detailed histories of prenatal, neonatal, and early childhood events were systematically reviewed through direct interviews with the patients. Patients were initially evaluated with noninvasive methods, including scalp EEG monitoring to capture spontaneous seizures and MRI. MRI was performed using a 1.5 T scanner and included axial images parallel to the long axis of the hippocampus. Ipsilateral and contralateral hippocampal images were visually compared to confirm mesial temporal sclerosis （MTS）. EEG recording and analysis Noninvasive data （scalp EEG and MRI） identified the mesial temporal region and a neocortical lesion site as the most likely ictal onset zones. Thus, all 11 patients were examined by implanted intracranial electrodes. To investigate the mesial temporal region, we used a stereo- eletroencephalography procedure. Depth electrodes were orthogonally directed through the middle temporal gyrus with the deepest contacts in the amygdala and anterior hippocampus. The number of neocortical electrodes implanted varied depending on the target region. Electrode positions were confirmed by post-implantation neuroimaging.