title: [A comparative study on intraoperative electrocorticography with long-term intracranial EEG for localizing epileptogenic zone].
abstract: OBJECTIVE
  To discuss the localizing methods for epileptogenic zone with intraoperative electrocorticography (ECoG) by comparing it with long-term intracranial EEG.
  
  
  METHODS
  Twenty-two patients was enrolled, who received epilepsy surgeries consecutively in our institute since April 2005 to August 2006. All patients underwent intracranial electrode implantations with long-term video-EEG monitoring before the resective surgeries and the postoperative pathologies were all proved to be focal cortical dysplasia. The extra-operative and ECoG digital EEGs were statistically analyzed and compared with each other, including interictal epileptic discharge (IED) frequency, amplitude and their correlations with ictal discharge (ID).
  
  
  RESULTS
  In the long-term intracranial EEG, significant difference was found between IED frequency derived from ID onset verus none-onset electrodes (Z = 12.213, P < 0.001), ROC analysis showed that IED frequency is a moderately good indicator for ID, the area under the ROC curve was 0. 758 (95% CI, 0.707-0.810). There was significant difference in IED amplitude between ID and none-ID electrodes (Z = 11.765, P < 0.001). The IED frequency was significantly lower during ECoG than during long-term extra-operative monitoring (rho = 0.518, P = 0. 014). A significant positive correlation in the IED frequency pattern was found between intra-operative ECoG and extra-operative recording when the average IED frequency was over 3 spikes /min. In ECoG, the correlation of IED with ID was similar in the 'frequent' (> or = 10 spikes/min) and 'occasional' (3-10 spikes/min) groups and very different in the 'rare' (< or = C3 spikes/min) group (rho = 0.408, P = 0.147).
  
  
  CONCLUSIONS
  The IED from long-term EEG recording had moderate correlation in frequency and amplitude with ID position. IED frequency was usually decreased on ECoG when compared with long-term monitoring. However, ECoG could reliably reflect the IED pattern and the correlations between IED with ID in term of frequency and amplitude in the long-term EEG monitoring, when IED frequency exceeded 3 spikes/min. Under this circumstance, IED could be used for localizing the epileptogenic zone.
authors.affiliation: Beijing Institute of Functional Neurosurgery, Xuanwu Hospital, Capital Medical University, Beijing 100053, China. cailx1010@hotmail.com
authors.forename: Li-Xin
authors.initials: LX
authors.lastname: Cai
authors.forename: Yong-Jie
authors.initials: YJ
authors.lastname: Li
authors.forename: Guo-Jun
authors.initials: GJ
authors.lastname: Zhang
authors.forename: Tao
authors.initials: T
authors.lastname: Yu
authors.forename: Wei
authors.initials: W
authors.lastname: Du
mesh_terms: D000293:Adolescent; D000328:Adult; D002540:Cerebral Cortex / Q000503:physiopathology; D002648:Child; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods*; D004828:Epilepsies, Partial / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D016343:Monitoring, Intraoperative; D012189:Retrospective Studies