NI-10 T2/FLAIR mismatch sign and methionine PET uptake in grade II and III gliomas

Background: Recent study suggests that “T2/FLAIR mismatch” sign is specific MRI finding for isocitrate dehydrogenase mutated (IDH-mut) 1p19q non-codeleted gliomas (Grade II and III astrocytic tumors). T2/FLAIR mismatch sign may be useful for predicting the histological type of glioma before surgery. However, it is not known what this finding reflects. Therefore, we examined the correlation between T2/FLAIR mismatch sign and uptake of methionine with positron emission tomography (MET-PET), and molecular classification of glioma. Methods: 74 glioma patients (grade II: 30 cases, grade III: 44 cases) with preoperative MRI and MET-PET who underwent surgical resection during 2000–2019 were included in this study. MR scans were evaluated by 3 independent reviewers to assess presence/absence of T2/FLAIR mismatch sign. The tumor-to-normal (T/N) ratio of methionine uptake was calculated by dividing the maximum standardized uptake value (SUV) for the tumor by the mean SUV of the normal brain. We examined the relationship between IDH mutation, 1p/19q codeletion, mismatch, and T/N ratio of MET-PET. Results: Out of the 74 cases, astrocytic tumors (A group: IDH-mutant, 1p19q non-codeleted) were 21 (28%), oligodendroglial tumors (O group: IDH-mutant, 1p19q codeleted) were 19 (26%), and IDH wild tumors (W group) were 34 (46%). The T2/FLAIR mismatch sign was present in 16 cases (22%). The T/N ratio of MET-PET in the tumor with T2/FLAIR mismatch sign was 1.56, which was significantly lower than that in the tumor without mismatch sign (2.01, p=0.016). T2/FLAIR mismatch sign was found in 7 (33%) cases in the A group, 0 (0%) case in the O group and 9 (26%) cases in the W group, and the positive rate was significantly higher in the A group (p=0.013). Conclusions: “T2/FLAIR mismatch” sign was a specific finding for astrocytic tumor, and the cases with positive “T2/FLAIR mismatch” sign had significantly lower MET-PET uptake than that with negative cases.