Methionine PET Findings in the Diagnosis of Brain Tumors and Nontumorous Mass Lesions: A Single-Center Report on 426 Cases.
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BACKGROUND AND PURPOSE: Differentiating between a brain tumor and a nontumorous lesion remains a diagnostic challenge, particularly when conventional imaging modalities such as CT and MRI provide inconclusive results. While 11C-methionine PET (MET-PET) has shown potential in neuro-oncology, its diagnostic performance across a broad spectrum of brain pathologies has not been comprehensively evaluated. This study, therefore, assessed the sensitivity, specificity, and uptake patterns of MET-PET in a large cohort of brain lesions. MATERIALS AND METHODS: This single-center retrospective study analyzed 426 consecutive patients with undiagnosed brain lesions who underwent MET-PET imaging between January 2019 and May 2024. Tumor-to-normal region ratios (TNRs) were calculated by using a threshold of 1.5 for positive findings. Histologic diagnoses were established on the basis of the World Health Organization 2021 criteria, including isocitrate dehydrogenase (IDH) mutation status and 1p/19q-codeletion. RESULTS: Among the cohort, 342 cases (67.8%) were confirmed as having tumorous lesions; 76 (17.8%), as having nontumorous lesions; and 61 (14.3%) remained undiagnosed. MET-PET exhibited high sensitivity (86.2%) but limited specificity (47.4%) for tumor detection. In multiple sclerosis cases, MET-PET showed a remarkably high positivity rate (n = 10/12) that was significantly higher than for other nontumorous lesions. In terms of tumors, IDH wild-type glioblastomas had significantly higher TNRs compared with IDH-mutant gliomas, while oligodendrogliomas had higher TNRs compared with astrocytomas, in which TNR values correlated with tumor grade. CONCLUSIONS: MET-PET demonstrated robust sensitivity for brain tumor detection but was limited by low specificity due to false-positives in inflammatory conditions and false-negatives for low-grade tumors. These findings imply the importance of integrating MET-PET with other imaging modalities to enhance diagnostic accuracy.