PhD student Virginia-Maryland College of Veterinary Medicine, Virginia Tech blacksburg, Virginia, United States
Abstract:
Background: In humans, the T2-FLAIR mismatch sign (T2FMM) is a specific imaging biomarker for IDH1-mutated, 1p19q non-codeleted low-grade astrocytomas (LGA). The T2FMM is characterized by a homogeneous hyperintense T2W signal and a hypointense signal with a hyperintense peripheral rim on FLAIR sequences. In canine gliomas, the T2FMM has not been described. Hypotheses/
Objectives: In dogs with focal intra-axial brain lesions, T2FMM will discriminate gliomas from other pathologies. The T2FMM will be associated with the LGA phenotype and presence of microcysts on histopathology. Interobserver agreement for T2FMM MRI features will be high. Animals: 186 dogs with focal intra-axial lesions on brain MRI; 146 with histologically confirmed oligodendrogliomas (n=90), astrocytomas (n=47), undefined gliomas (n=9), 33 with cerebrovascular accidents, and 7 with inflammatory lesions.
Methods: Two blinded raters evaluated the 186 MRI studies retrospectively to identify cases with the T2FMM. Histopathologic and immunohistochemical slides of T2FMM cases were evaluated for morphologic features and IDH1-mutations and compared to cases without the T2FMM. Gene expression analyses were performed on a subset of oligodendrogliomas (n=10) with and without T2FMM.
Results: T2FMM was identified in 14/186 (8%) of MRI, and all dogs with T2FMM had oligodendrogliomas (n=12 low-grade [LGO], n=2 high-grade [HGO]; P < .001). Microcystic change was significantly associated with the T2FMM (P < 0.00001). In oligodendrogliomas with T2FMM, IDH1-mutations or specific differentially expressed genes were not identified. Conclusion and clinical importance: T2FMM can be readily identified on routinely obtained MRI sequences. T2FMM is a specific biomarker for canine oligodendroglioma, and was significantly associated with non-enhancing LGO.
