Invasive EEG

Abstract

A synoptic assessment about intracranial invasive procedures is provided: particularly general and specific indications, most utilized methodologies, risks, and morbidity/mortality of the different techniques. In the context of focal pharmaco-resistant epilepsies, surgical resection of the epileptogenic zone (EZ) is the only therapeutic option for suppressing seizures. The aim of epilepsy surgery is the complete exeresis of the EZ, which is assumed to represent the cortical region responsible for the onset, early seizures organization, and propagation of ictal discharges and represents the minimum amount of cortex to be resected in order to achieve seizure freedom. Therefore the correct identification of its extent and organization remains a crucial objective. In many patients, intracranial/intracerebral invasive EEG (iEEG) recordings still represent the gold standard for the complete and exhaustive epilepsy surgery work-up, and, over the last years, considerable efforts have been made to develop advanced techniques able to improve the identification of the EZ. Many arguments can lead to the final decision to submit the patient to invasive recordings, a surgical procedure with both risks and surgical perspectives: in particular any discrepancies between anatomo-electro-clinical data, a negative MRI and a EZ close to high-functioning cortical areas. Two major approaches and methodologies are at present favored: subdural electrodes, requiring a large bone hole, and the positioning of grids and or strips, depending on the supposed localization of the EZ. Surgery is performed at the end of invasive recordings. The second one, SEEG, is considered a “three-dimensional” methodology, exploring predominantly network and connection between EZ and distant cortical areas, efficacy only if the primary hypothesis was correctly explored. Surgery can be delayed with respect to iEEG. Nowadays some epilepsy surgery centers highest in volume offer both SE and SEEG as intracranial strategies for seizure localization, depending on the patient particularity. The choice in between these two techniques is complex; it depends on the intrinsic patient characteristics but mostly on the peculiar experience of the epilepsy surgical unit. Methodologies, risks with advantages, and limits are discussed.