Background: Medically refractory, magnetic resonance imaging (MRI)-negative mesial temporal lobe epilepsy presents a diagnostic challenge, often leading to difficulties in localizing the epileptogenic zone and planning effective surgical strategies. Case Description: We present a case in which complementary preoperative and intraoperative electrophysiological analyses identified an occult epileptogenic focus. Preoperative high-density scalp electroencephalogram evaluated with gamma oscillation regularity (GOR) analysis localized a putative epileptogenic region adjacent to the hippocampus. Guided by this localization, intraoperative electrocorticography was analyzed using GOR-based transfer entropy (TE). This mapping revealed a compact hub of consistent outgoing directed information flow localized to the parahippocampal gyrus. The surgical strategy targeted the GOR-based TE-defined parahippocampal focus and its immediate efferent connections while preserving the hippocampus. The patient remains seizure-free with preserved neurocognitive function at follow-up. Conclusion: This case demonstrates that preoperative GOR analysis can noninvasively direct focused intraoperative network interrogation and that GOR-based TE-derived directed connectivity mapping can unmask mesial temporal epileptogenicity in MRI-negative cases, thereby guiding effective, tissue-sparing resections.
Yosuke Sato (Fri,) studied this question.