Ictal EEG source imaging and connectivity to localize the seizure onset zone in extratemporal lobe epilepsy

Seizure. 2020 May:78:18-30. doi: 10.1016/j.seizure.2020.03.001. Epub 2020 Mar 4.

Abstract

Purpose: To evaluate the yield of Functional Connectivity (FC) in addition to low-density ictal Electrical Source Imaging (ESI) in extratemporal lobe epilepsy (ETLE), using an automated algorithm for analysis.

Method: Long-term EEG monitoring of consecutive ETLE patients who underwent surgery was reviewed by epileptologists, and seizure onsets characterized by rhythmical activity were identified. A spectrogram-based algorithm was developed to select objectively the parameters of ESI analysis. Two methods for SOZ localization were compared: i) ESI power, based on LORETA exclusively; ii) ESI + FC, including a Granger causality-based connectivity analysis. Results were determined at a sublobar level. The resection zone, in relation to 1-year follow-up surgical outcome, was considered as reference standard for diagnostic accuracy analyses.

Results: Ninety-four seizures from 24 patients were analyzed. At seizure-level, ESI power showed 36 % sensitivity and 72 % specificity (accuracy: 45 %). ESI + FC significantly improved the accuracy, with 52 % sensitivity and 84 % specificity (accuracy: 61 %, p = 0.04). Results of ESI + FC were equally valuable in patients with lateralized or bilateral/generalized visual interpretation of ictal EEG. In a patient level sub-analysis, upon blinded clinical interpretation, ESI + FC showed a correct localization in 67 % of patients and substantial inter-rater agreement (kappa = 0.64), against 27 % achieved by ESI power, with fair inter-rater agreement (kappa = 0.37).

Conclusion: FC significantly improves SOZ localization compared to ESI solely in ETLE. Ictal ESI + FC could represent a novel option in the armamentarium of presurgical evaluation, aiding also in patients with visually non-localizable scalp ictal EEG. Prospective studies evaluating the clinical added value of automated low-density ictal ESI may be justified.

Keywords: Automated ESI; Electrical source imaging; Functional connectivity; Granger causality; Presurgical evaluation.

MeSH terms

  • Adolescent
  • Adult
  • Cerebral Cortex* / physiopathology
  • Child
  • Connectome / methods*
  • Connectome / standards
  • Drug Resistant Epilepsy / diagnosis*
  • Drug Resistant Epilepsy / physiopathology
  • Drug Resistant Epilepsy / surgery
  • Electroencephalography / methods*
  • Electroencephalography / standards
  • Epilepsies, Partial / diagnosis*
  • Epilepsies, Partial / physiopathology
  • Epilepsies, Partial / surgery
  • Female
  • Follow-Up Studies
  • Humans
  • Magnetic Resonance Imaging
  • Male
  • Middle Aged
  • Sensitivity and Specificity
  • Young Adult