Abstract
OBJECTIVE: Epileptic seizures are common in patients with low-grade gliomas (LGGs). (11)C-methionine (MET) is a radiolabeled amino acid tracer commonly used in positron emission tomography (PET), and MET-PET is a valuable tool for the clinical characterization of gliomas. This study aimed to evaluate the factors associated with MET uptake in patients with suspected LGG and, specifically, to characterize MET uptake in the presence or absence of epilepsy. METHODS: MET uptake on preoperative MET-PET images was retrospectively reviewed in 40 patients with a presurgical diagnosis of LGG based on the absence of gadolinium enhancement on MRI. All patients underwent surgery and had their pathological diagnosis confirmed. The correlation between MET uptake and the occurrence of seizures in patients with LGGs was investigated during their clinical course. The ratio of the lesion to the contralateral normal region (L/N ratio) was calculated by dividing the maximum standardized uptake value of the tumor by the value of the contralateral region. Clinical parameters and MET uptake data were extracted from the medical records. RESULTS: The mean age of the patients was 48 years (range: 21-90 years), consisting of 26 males and 14 females. Preoperative seizures and 1p/19q codeletion were correlated with higher MET uptake (p < 0.01). Grade 2 oligodendrogliomas had significantly higher MET uptake than grade 2 astrocytomas and glioblastomas (p < 0.01). In particular, grade 2 oligodendrogliomas with preoperative seizures showed approximately twofold higher MET uptake than those without preoperative seizures (L/N ratio 2.01 vs. 1.20, p = 0.042). The optimal cutoff value of the lesion-to-contralateral-normal ratio of MET uptake for predicting preoperative seizures was 2.13, as calculated using a receiver operating characteristic curve and an area under the curve. Conversely, grade 2 astrocytoma and glioblastoma with or without seizures (L/N ratio 1.44 vs. 1.09, 1.40 vs. 1.34), as well as oligodendroglioma without seizures (L/N ratio 1.33), showed similar MET uptake. CONCLUSIONS: An epileptogenic formation mechanism may be involved in the increased uptake of MET in oligodendrogliomas. In patients with suspected LGGs, if there is a significant increase in MET uptake, the possibility of an oligodendroglioma should be considered and attention should be paid to the risk of epileptic seizures.