Abstracts

Rationale: Successful epilepsy surgery requires the identification of the epileptogenic zone and the definition of eloquent cortex. Invasive EEG monitoring with intracranial EEG recording electrodes to record electrocorticography (ECOG) is often needed. Successful invasive monitoring is fraught with technical complications. One particular technical difficulty occurs with the ground and reference electrodes; typically these are applied to the body surface. Ideally, the recording and ground electrodes should be the same material, otherwise artifact is introduced. We had encountered frequent artifact with ECOG and tested an alternative subgaleal ground and reference recording electrode method. Methods: We utilized a 4 contact (1 X 4) intracranial electrode strip placed inverted within the subgaleal space for the ground and reference electrodes for ECOG. We performed a retrospective audit of the technical quality of the ECOG and complications from invasive monitoring from five patients before and five patients after the utilization of this inverted 1 X 4 subgaleal recording strip. Recordings were assessed for EEG artifact, which included 60Hz artifact, movement artifact, artifact from electronic devices, voltage fluctuation and voltage overload (EEG flattening). Recordings were scored as excellent (minimum artifact in cortical and surface electrodes with no re-gelling needed), fair (interpretable with minimal artifact, less than 5 minutes per hour) or bad (portions un-interpretable due to frequent artifacts that obscure waveforms). Results: The ages and recording duration ranged from 3 to 18 years and from 48 to 140 hours prior to the standard ground recording method and from 4 to 16 years and from 72 to 168 hours after the new method. EEG quality was assessed as excellent in all five recordings performed after the use of the intracranial recording strip and only fair in all five recordings using the standard reference electrodes. There were no complications associated with this inverted 1X4 subgaleal recording electrode strip. Conclusions: The technical quality of the ECOG dramatically improved after the utilization of a subgaleal recording electrode method compared to the standard surface electrode method. Our results demonstrate the efficacy and safety of this alternative subgaleal recording system. We now utilize this method for all invasive monitoring cases.