The T2-FLAIR mismatch sign in IDH-mutant astrocytomas - Is there an association with FET PET uptake?

Ziel/Aim The purpose of this study was (i) to assess the reproducibility of the previously described T2-FLAIR mismatch sign as a highly specific MR imaging marker in non-enhancing IDH-mutant, 1p/19q non-codeleted lower-grade gliomas (LGG) of the WHO grades II or III, and (ii) its association with the uptake of the radiolabeled amino acid O-(2-[¹⁸F]-fluoroethyl)-L-tyrosine (FET) in PET to further metabolically characterize that sign, which is currently poorly understood.

Methodik/Methods Consecutive MRI and dynamic FET PET scans (n = 134) from newly diagnosed and neuropathologically confirmed IDH-mutant LGG (n = 65) and IDH-wildtype gliomas as control group (n = 69) were evaluated by two independent raters to assess presence/absence of the T2-FLAIR mismatch sign as well as FET uptake. Interrater agreement was assessed using Cohen’s kappa (κ), as well as diagnostic performance (i.e., positive/negative predictive value; PPV, NPV) of the T2-FLAIR mismatch sign to identify IDH-mutant astrocytomas.

Ergebnisse/Results In the LGG group, 13 patients (20 %) had a T2-FLAIR mismatch sign, which could be identified with a substantial interrater agreement (κ=0.75). In contrast, that sign was absent in IDH-wildtype gliomas. All 13 cases that were positive for the T2/FLAIR mismatch sign were IDH-mutant, 1p/19q non-codeleted tumors (PPV = 100 %, NPV = 57 %). Interestingly, the sign was significantly (P = 0.027) associated with a negative FET PET scan (i.e., 5 tumors with indifferent FET uptake comparable to the background activity, or FET uptake below background activity (photopenic defect) in 5 tumors).

Schlussfolgerungen/Conclusions With a robust interrater agreement, our findings are in line with previously reported findings regarding the T2-FLAIR mismatch sign. Additionally, the T2-FLAIR mismatch sign seems to be significantly related with a lack of increased FET uptake in PET, which may help to further characterize patients with that sign. Notwithstanding, the clinical relevance of this imaging constellation warrants further investigation.