Background and Purpose
Lower-grade gliomas (LGG) have been classified into molecular subtypes with different prognosis based on the IDH1/2 mutation status and 1p/19q codeletion status. The T2-FLAIR mismatch has been proven to be a highly specific imaging biomarker for the IDH-mutant, 1p/19q non-codeleted genotype; however, this conclusion has been drawn from studies utilizing non-contrast FLAIR images. The signal intensity in FLAIR sequences depends on both T1 and T2 relaxation times, and contrast-enhanced FLAIR (ceFLAIR) has been proven to increase the conspicuity of certain cerebral and meningeal lesions. We aimed to investigate whether the T2-FLAIR mismatch sign utilizing ceFLAIR images rendered a comparable diagnostic performance.

Materials and Methods
Preoperative MR scans of 18 adult patients with pathological diagnosis of LGG (WHO grade II and III) with known IDH1/2 status, 1p/19q codeletion status, and ceFLAIR images were included (6 IDH1/2-Mut, 1p/19q codeleted; 8 IDH1/2-Mut, 1p/19q non-codeleted; 4 IDH1/2-WT). The MR scans were evaluated to assess the presence of the T2-FLAIR mismatch sign by two blinded neuroradiology trainees and one blinded neuroradiologist. A consensus decision was made in regards to the presence or absence of the sign. 

Results
The T2-FLAIR mismatch sign was present in 3/8 cases of 8 IDH1/2-Mut, 1p/19q non-codeleted LGG. The sign was not seen in the remaining 5 patients with IDH1/2-Mut, 1p/19q non-codeleted,  6 individuals with IDH1/2-Mut-1p/19q codeleted, and 4 sibjects with IDH1/2-WT LGG. The T2-FLAIR mismatch sign utilizing ceFLAIR had a positive predictive value of 100%, negative predictive value of 66% (95% CI = 53.90-77.38), a sensitivity of 37.5% (95% CI = 8.52-75.51), and a specificity of 100% (95% CI = 69.15-100.00).

Conclusion 
The T2-FLAIR mismatch is a highly specific imaging marker for IDH1/2-Mut, 1p/19q non-codeleted LGG, which concurr with the results published in prior studies. T2-FLAIR mismatch sign utilizing ceFLAIR images renders similar diagnostic performance when compared with studies done with standard non-contrast FLAIR acquisitions.

T2-FLAIR Mismatch sign as an imaging biomarker for IDH-mutant, 1p/19q non-codeleted lower-grade gliomas. Initial experience utilizing contrast-enhanced FLAIR acquisition

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