Dysembryoplastic neuroepithelial tumor (DNET) is a benign tumor that causes intractable epilepsy at young ages. In this report, we present a rare case of a 28-year-old female with a DNET in the temporal lobe showing extracortical extension to the basal cistern. Enlarging contrast enhancement on MRI, a trait unusual for a benign tumor, suggested the possibility of a malignant glioma. An intraoperative rapid pathological diagnosis of a low-grade glioma in conjunction with electrocorticographic findings supported a surgical strategy of tumor resection alone with preservation of the hippocampus. For this type of DNET with uncommon extension and MRI features, a combination of electro-physiological and morphological analyses based on preoperative studies for epileptogenic focus detection is key to achieving good seizure control and tumor removal with preservation of the patient's memory function.