Visualizing epileptogenic regions using the chemical exchange saturation transfer method in a patient with drug-resistant focal epilepsy: a case report.

Abstract

Background: Sustained elevations in extracellular glutamate levels within astrocytes may precipitate epileptic seizures. In this report, chemical exchange saturation transfer imaging was used to measure brain glutamate concentrations in a patient who underwent focal resection surgery.

Case presentation: A male Japanese patient in his 30s with drug-resistant focal epilepsy underwent preoperative assessment at our institute. Preoperative magnetic resonance imaging was performed using an ultra-high-field magnetic resonance imaging system. The results of intracranial electroencephalography and chemical exchange saturation transfer imaging were compared. Head magnetic resonance imaging revealed no abnormalities. However, fluorodeoxyglucose-positron emission tomography revealed reduced glucose metabolism in the distal left temporal lobe. Preoperative fluorodeoxyglucose-positron emission tomography and intracranial electroencephalography indicated abnormal interictal waves and identified the seizure onset site. Ablation was performed from the distal to the basal region of the temporal lobe. Pathological examination revealed focal cortical dysplasia type IIa. Chemical exchange saturation transfer imaging delineated an elevated glutamate concentration extending from the distal tip of the left temporal lobe to the medial temporal lobe. These regions included the areas of seizure onset identified by intracranial electroencephalography and matched the extent of the resection surgery. Four months postoperatively, focal aware seizures recurred; however, no focal impaired awareness seizures were observed at 1 year postoperatively. Elevated glutamate levels were detected in the hippocampus head, suspected to be associated with residual focal aware seizures.

Conclusion: Glutamate-chemical exchange saturation transfer magnetic resonance imaging was used to noninvasively measure brain glutamate concentrations, providing new insights into identifying epileptogenic zones when conventional imaging techniques fail.