Intracranial Electroencephalographic Monitoring: From Subdural to Depth Electrodes

Abstract

At the London Health Sciences Centre Epilepsy Program, stereotactically implanted depth electrodes have largely replaced subdural electrodes in the presurgical investigation of patients with drug-resistant epilepsy over the past 4 years. The rationale for this paradigm shift was more experience with, and improved surgical techniques for, stereoelectroencephalography, a possible lower-risk profile for depth electrodes, better patient tolerability, shorter operative time, as well as increased recognition of potential surgical targets that are not accessible to subdural electrodes.

Seizure Freedom in Temporal Plus Epilepsy Surgery Following Stereo-Electroencephalography

“…The identification of additional TPE cases among our pool of failed TLE surgery cases is limited due to the fact that SEEG has taken over as the preferred method for intracranial investigation at our center only recently, since 2013. 23 This means that more failed cases are currently under re-evaluation and are waiting for SEEG. Although subdural strips can identify some of the extratemporal foci in addition to the temporal focus, the insula would remain unsampled.…”

Recent Advancement of Technologies and the Transition to New Concepts in Epilepsy Surgery

“…It took only 5 years to replace SDE with SEEG. 12) It seems to be the same trend in Japan, because the Japan Ministry of Health, Labor and Welfare approved reimbursement as insurance coverage for robot-assisted placement of depth electrodes for SEEG early in 2020. However, many groups outside Europe may be unfamiliar with SEEG.…”

“…Another method is SEEG, which is more popularized worldwide in the last decade. 3,11,12) SEEG is usually performed only with depth electrodes without craniotomy ( Figs. 2 and 3).…”

On the Renaissance of Stereotactic EEG and Its Interpretation

“…8 It is important to keep in mind that the long history of epilepsy surgery excellence at LHSC, before the shift to SEEG, comprises 30 years of fruitful IEEG monitoring using subdural electrodes. 8,9 A future analysis of seizure outcomes comparing pre-and post-SEEG eras at LHSC will be extremely valuable to see the long-term impact of the transition in techniques on outcomes in patients receiving epilepsy surgery. Ideally, of course, other future studies will be designed to compare IEEG modalities, including randomized clinical trials.…”

“…4,8,10 Another issue arising in the choice of IEEG modalities is related to the hypothesis arrived at before implantation and the expertise of the epileptologist. 8,12 Because a smaller area is potentially covered with depth electrodes, a more refined hypothesis may be required in SEEG, although typically several depth electrodes are implanted and what is lost in two-dimensional cortical surface coverage may be gained in threedimensional cortical-subcortical-cortical coverage. 3,[10][11][12] Often forgotten in the discussions surrounding different IEEG modalities is the role of the clinical neurophysiologist interpreting the recordings.…”