Quantification of Epileptogenic Network From Stereo EEG Recordings Using Epileptogenicity Ranking Method

Abstract

Introduction: Precise localization of the epileptogenic zone is very essential for the success of epilepsy surgery. Epileptogenicity index (EI) computationally estimates epileptogenicity of brain structures based on the temporal domain parameters and magnitude of ictal discharges. This method works well in cases of mesial temporal lobe epilepsy but it showed reduced accuracy in neocortical epilepsy. To overcome this scenario, in this study, we propose Epileptogenicity Rank (ER), a modified method of EI for quantifying epileptogenicity, that is based on spatio-temporal properties of Stereo EEG (SEEG).Methods: Energy ratio during ictal discharges, the time of involvement and Euclidean distance between brain structures were used to compute the ER. Retrospectively, we localized the EZ for 33 patients (9 for mesial-temporal lobe epilepsy and 24 for neocortical epilepsy) using post op MRI and Engel 1 surgical outcome at a mean of 40.9 months and then optimized the ER in this group.Results: Epileptic network estimation based on ER successfully differentiated brain regions involved in the seizure onset from the propagation network. ER was calculated at multiple thresholds leading to an optimum value that differentiated the seizure onset from the propagation network. We observed that ER < 7.1 could localize the EZ in neocortical epilepsy with a sensitivity of 94.6% and specificity of 98.3% and ER < 7.3 in mesial temporal lobe epilepsy with a sensitivity of 95% and specificity of 98%. In non-seizure-free patients, the EZ localization based on ER pointed to brain area beyond the cortical resections.Significance: Methods like ER can improve the accuracy of EZ localization for brain resection and increase the precision of minimally invasive surgery techniques (radio-frequency or laser ablation) by identifying the epileptic hubs where the lesion is extensive or in nonlesional cases. For inclusivity with other clinical applications, this ER method has to be studied in more patients.

Interictal Discharges: All Roads Lead to Rome?

“… 7 There is often dissociation between the topography of IEDs and the SOZ, and it is generally recognized that the IZ is larger than the SOZ. 8 , 9 IZs could extend to brain regions much larger than the SOZ as well as to spatially distant sites where seizures may jump to non-adjacent leads during propagation. The clinical significance of the analysis presented in this manuscript is that IEDs can be used to identify the SOZ.…”

Improving epileptogenic zone estimation using Bayesian inference on neural field models

“…Identification of seizure onset zone using purely data driven signal analysis of SEEG time series such as EI, EM and ER [2, 3, 5] are by construction spatially constrained to identify EZ within the implanted regions. Similar to previous VEP studies [16, 18, 17, 31], the generative model used in this study also includes a forward model, the so called the gain matrix, transforming latent source activity to the SEEG time series.…”

Stereoelectroencephalography-Guided Radiofrequency Thermocoagulation: Diagnostic and Therapeutic Implications

“…Several groups [65,66] have begun utilizing network ablation strategies with some success. Improvements in intracranial recording evaluation will likely further benefit this strategy; epileptogenic zone fingerprint analysis [67], epileptogenicity ranking methods [68], and advanced computational measures [69] are examples of new methodologies for discriminating epileptogenic tissue.…”