Electric source imaging for presurgical epilepsy evaluation: current status and future prospects

ABSTRACT

Introduction: Electric source imaging (ESI) refers to the estimation of the cerebral sources of electric signals recorded at the head surface using electroencephalography (EEG). Thanks to the availability of EEG systems with high numbers of electrodes and to progress in software to analyze the signals they collect, ESI can be applied to epilepsy-related pathological EEG signals like interictal spikes and seizures.

Areas covered: In this narrative review, we discuss selected original research articles on the use of ESI in epilepsy patients considered for surgery. Epilepsy-related activity can be localized accurately using ESI, as established by comparison to the gold standards of intracranial EEG and seizure control following epilepsy surgery. The information brought by ESI complements successfully that of other techniques like magnetic resonance imaging and positron-emission tomography, and is clinically relevant to patient management.

Expert opinion: EEG is a readily available technique to measure brain activity in real time. Given its accuracy and usefulness, ESI should become part of the routine practice of clinical neurophysiology laboratories and epilepsy centers in the presurgical management of epilepsy patients.

KEYWORDS:

• Electric source imaging
• electroencephalography
• high-density EEG
• source localization
• inverse solution
• epilepsy
• interictal epileptiform discharges
• epileptic seizures
• epilepsy surgery

Article Highlights

• Electric source imaging of high-density EEG signals has been demonstrated to localize accurately the source of epilepsy-related EEG activity such as interictal spikes and seizures.

• Including ESI in the assessment of patients with drug-resistant focal epilepsy who are candidates for epilepsy surgery enriches the amount of information available. This additional information influences significantly the clinical management of these patients when deciding on an operation or planning an intracranial EEG evaluation. Furthermore, ESI might play a role in selecting patients for surgery by helping predict surgical outcomes in terms of freedom from seizures.

• As of today, ESI remains a technically demanding investigation. However, improvements in the development of hardware for high-density EEG and of software for signal analysis are ongoing. Consequently, the technique could soon become a routine tool available in every clinical neurophysiology laboratory and epilepsy center.

Declaration of Interest

M Seeck holds shares in Epilog, and was a speaker for Philips and Desitin. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer Disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was funded by the Swiss National Science Foundation [grant no. 167836 to P Mégevand; grant nos. 163398, 180365 to M Seeck] and the Fondation Privée des Hôpitaux Universitaires de Genève.