[Intracranial EEG monitoring methods]

Resective surgery is considered to be the best option towards achieving seizure-free state in drug-resistant epilepsy. Intracranial EEG (iEEG) is necessary if the seizure-onset zone is localized near to an eloquent cortical area, or if the results of presurgical examinations are discordant, or if an extratemporal epilepsy patient is MRI-negative. Nowadays, 3 kinds of electrodes are used: (1) foramen ovale (FO) electrodes; (2) subdural strip or grid electrodes (SDG); (3) deep electrodes (stereo-electroencephalographia, SEEG). The usage of FO electrode is limited to bitemporal cases. SDG and SEEG have a distinct philosophical approach, different advantages and disadvantages. SDG is appropriate for localizing seizure-onset zones on hemispherial or interhemispherial surfaces; it is preferable if the seizure-onset zone is near to an eloquent cortical area. SEEG is excellent in exploration of deeper cortical structures (depths of cortical sulci, amygdala, hippocampus), although a very precise planning is required because of the low spatial sampling. The chance for seizure-freedom is relatively high performing both methods (SDG: 55%, SEEG: 64%), beside a tolerable rate of complications.