Mesial temporal involvement in epidermoid tumor-related temporal lobe epilepsy revealed by stereoelectroencephalography: illustrative case.

BACKGROUND: Intracranial epidermoid tumors are rare benign lesions that are typically nonepileptogenic; however, temporal lobe involvement may result in drug-resistant epilepsy. The relationship between the lesion and the epileptogenic network remains poorly understood, particularly due to limited electrophysiological evaluation of mesial temporal structures. OBSERVATIONS: A 52-year-old left-handed woman with drug-resistant temporal lobe epilepsy associated with an epidermoid tumor underwent staged surgical management. Initial resection of the posterior fossa component achieved histopathological diagnosis and brainstem decompression. Subsequent stereoelectroencephalography (SEEG) demonstrated seizure onset involving the hippocampal head and body and the mesial posterior temporal region. Functional mapping revealed language involvement in the posterior temporal cortex. Based on these findings, an anterior temporal lobectomy with partial hippocampal resection was performed to preserve cognitive function. Postoperatively, no new neurological deficits were observed and the patient achieved International League Against Epilepsy class III outcome, with seizures reduced to auras and a single focal impaired consciousness seizure. LESSONS: Epileptogenic networks in epidermoid tumor-related temporal lobe epilepsy may extend beyond the lesion to involve mesial temporal structures. This case highlights hippocampal involvement and the value of a staged SEEG-guided approach for identifying deep epileptogenic regions and guiding tailored surgical strategies, particularly in dominant hemisphere cases. https://thejns.org/doi/10.3171/CASE26341.