Defining Network Epilepsy and Surgical Outcomes Following Resection or Ablation of Seizure Onset Zone(s); A Case Series

Introduction: Patients with unifocal epilepsies are common candidates for microsurgical resection of their seizure onset zones (SOZ), which affords the greatest likelihood of durable seizure freedom. Conversely, multifocal and generalized epilepsies are associated with poor outcomes. We introduce another category of patient with a particular subtype of multi-focal epilepsy, in which the epileptogenic zone is distributed across diverse brain regions, that we categorize as network epilepsies, and asses their electrophysiology and surgical outcomes.

Methods: Patients at our Level IV epilepsy center who underwent intracranial electroencephalography (EEG) recordings for SOZ localization and treated with surgical ablation/resection from 2004-2024 were reviewed. Using EEG, network epilepsy was defined as having greater than 1 distinct foci that could independently produce seizures and propagate to other foci. Perioperatively, all regions were ablated/resected. A desirable outcome was defined as scoring less than 3 on the ILAE scale.

Results: 365 intracranial EEG were performed followed by surgical treatment. Of which, 292 patients undergoing 309 intracranial EEG recordings (stereo-EEG: 166, subdural EEG: 114) were included. Of these, 200 had unifocal (68.5%), 27 regional (9.3%), 49 multifocal (16.8%), 1 generalized (0.3%), and 15 network (5.1%) epilepsy. 15 network epilepsy patients (18 total procedures) were subclassified as Temporal-Orbitofrontal (N=6), PVNH+ (N=5), Temporal-Posterior Quadrant (N=2), and Insular+ (N=2). Following surgery, 11 out of 15 patients (78.6%) had favorable outcomes (ILAE-1: N=9, ILAE-2: N=2) at last follow-up (median: 4 years, range 1-15 years). The remaining had decreased seizure frequency (ILAE-4: N=3). Surgical treatment for network epilepsy demonstrated similar rates of favorable outcomes compared to unifocal cohorts (N=112/200 favorable, p=0.52), and significantly better than multifocal (N=12/49, p< 0.01) and regional (N=6/27, p< 0.01) epilepsy.

Conclusion : Network epilepsies are a rare entity, identified in less than 5% of our cohort. An appreciation for this entity can enable multifocal surgical resection of the SOZs and yield durable seizure freedom.