Abstracts

Rationale: The role of epileptogenic networks in seizure propagation and generation, characterized by changes in global and regional connectivity across multiple, anatomically distant tubers, is increasingly recognized in tuberous sclerosis (TSC). Intracranial sampling with stereoelectroencephalography (sEEG) has made it possible to gain direct access to these epileptogenic networks, explore network dynamics and gain valuable insights into the surgical and clinical implications. The objective of this study is to define epileptic networks in TSC using quantitative analysis of sEEG recordings. Methods: Intracranial sEEG recordings were obtained from pediatric patients who presented with medically refractory epilepsy secondary to TSC and subjected to quantitative signal analysis methods. Cortical connectivity was quantified by calculating pairwise coherence between all contacts and constructing an association matrix. The global coherence, defined as the ratio of the largest eigenvalue to the sum of all the eigenvalues, was calculated for each frequency band (delta, theta, alpha, beta, gamma). Spatial distribution of the connectivity was identified by plotting the leading principal component (product of the largest eigenvalue and its corresponding eigenvector). Seizure outcomes were determined based on Engel score. Results: Four pediatric subjects with TSC underwent intracranial monitoring with sEEG for localization of the epileptogenic focus and guidance of subsequent surgical intervention. A total of 31 depth electrodes comprising 250 contacts were implanted. Quantitative connectivity analysis revealed an increase in global coherence during the ictal period in the beta/low gamma (14 – 30 Hz) and high gamma (31 – 80 Hz) bands. Our results corroborate findings from existing literature, which implicate higher frequencies as a driver of synchrony and desynchrony. Following adequate localization of the epileptogenic focus, two patients underwent treatment with magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) and two patients were treated with surgical resection. All patients had Engel I outcome at the most recent follow-up. Conclusions: Epileptic networks, characterized by coordinated high frequency activity in the beta/low gamma and high gamma bands define the ictal period in TSC. This time-dependent increase in global coherence demonstrates evidence for intra-tuberal, inter-tuberal and peri-tuberal connectivity in TSC. These findings have surgical implications for targeted laser ablation or surgical resection of tubers. Funding: No funding