Correlation of invasive EEG and scalp EEG

Abstract

Ever since the implementation of invasive EEG recordings in the clinical setting, it has been perceived that a considerable proportion of epileptic discharges present at a cortical level are missed by routine scalp EEG recordings. Several in vitro, in vivo, and simulation studies have been performed in the past decades aiming to clarify the interrelations of cortical sources with their scalp and invasive EEG correlates. The amplitude ratio of cortical potentials to their scalp EEG correlates, the extent of the cortical area involved in the discharge, as well as the localization of the cortical source and its geometry have been each independently linked to the recording of the cortical discharge with scalp electrodes. The need to elucidate these interrelations has been particularly imperative in the field of epilepsy surgery with its rapidly growing EEG-based localization technologies. Simultaneous multiscale EEG recordings with scalp, subdural and/or depth electrodes, applied in presurgical epilepsy workup, offer an excellent opportunity to shed some light to this fundamental issue. Whereas past studies have considered predominantly neocortical sources in the context of temporal lobe epilepsy, current investigations have included deep sources, as in mesial temporal epilepsy, as well as extratemporal sources. Novel computational tools may serve to provide surrogates for the shortcomings of EEG recording methodology and facilitate further developments in modern electrophysiology.

Simultaneous scalp EEG improves seizure lateralization during unilateral intracranial EEG evaluation in temporal lobe epilepsy

“…Seizure: European Journal of Epilepsy 64 (2019) [8][9][10][11][12][13][14][15] hemispheric IEEG electrodes (CL-IEEG in this case) and scEEG were present. We hypothesized that in this hypothetical patient with left temporal seizures, the location criterion comparing bilateral scEEG and right hemispheric IEEG, would indicate incongruous locations of seizure onset, since the earliest EEG changes suggesting seizures would be noted in the left hemispheric scEEG electrodes and later in the right hemispheric IEEG.…”

“…We decided to use the same duration of 3 s of in our mixed cohort of mesial and neocortical temporal cases since no other criterion was available specifically A.R. Antony, et al Seizure: European Journal of Epilepsy 64 (2019) [8][9][10][11][12][13][14][15] for mesial temporal seizures. Lieb et al noted worse post-surgical outcome in patents with an interhemispheric propagation time of less than 5 seconds [30].…”

“…In another study involving 105 patients with temporal lobe epilepsy, 4.7% of seizures were falsely noted in the scEEG to originate in the opposite hemisphere [7]. However, scEEG recorded simultaneously during IEEG evaluation can provide valuable additional data, including predicting surgical outcome, spike detection, measurement of brain impedance, and localization of seizure onset zone [8][9][10][11][12][13][14][15]. Even though electrical potentials decrease with distance and vary with conduction rates of different tissues as proposed by Gauss' law, we believe that the clinical analysis of the correlations between the scEEG and IEEG recorded simultaneously can provide additional critical information not provided by reviewing IEEG and scEEG recorded separately.…”

“…Evaluation of the three criteria in a hypothetical patient with left temporal seizures who had right IEEG and bilateral scalp electrodes placed (see text for explanation). Sc EEG-scalp EEG, IEEG-intracranial EEG, SOZ-Seizure onset zone.A.R.Antony, et al Seizure: European Journal of Epilepsy 64 (2019)[8][9][10][11][12][13][14][15] …”

Epilepsiechirurgie bei Kindern und Jugendlichen

“…Zur genaueren Abgrenzung der epileptogenen Zone, z. B. bei fehlenden Hinweisen auf eine strukturelle Läsion im MRT, bei unklarer Ausdehnung einer Läsions-assoziierten epileptogenen Zone oder zur Kartierung von benachbarten eloquenten kortikalen Arealen, werden invasive Ableitungen durchgeführt [86]. Zwei grundsätzlich unterschiedliche Methoden zur invasiven Abklärung stehen zur Verfügung: Ableitungen mit subdural platzierten Streifen-oder Plattenelektroden [36,87,88] und Ableitungen mit intrazerebral platzierten Tiefenelektroden [36,53].…”