The T2‐FLAIR mismatch sign as an imaging biomarker for oligodendrogliomas in dogs

Abstract

Background In humans, the T2‐weighted (T2W)—fluid‐attenuated inversion recovery (FLAIR) mismatch sign (T2FMM) is a specific imaging biomarker for the isocitrate dehydrogenase 1 (IDH1)‐mutated, 1p/19q 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 gliomas in dogs, the T2FMM has not been described. Hypotheses/Objectives In dogs with focal intra‐axial brain lesions, T2FMM will discriminate gliomas from other lesions. The T2FMM will be associated with the LGA phenotype and presence of microcysts on histopathology. Interobserver agreement for T2FMM magnetic resonance imaging (MRI) features will be high. Animals One hundred eighty‐six dogs with histopathologically diagnosed focal intra‐axial lesions on brain MRI including oligodendrogliomas (n = 90), astrocytomas (n = 47), undefined gliomas (n = 9), cerebrovascular accidents (n = 33), and inflammatory lesions (n = 7). Methods Two blinded raters evaluated the 186 MRI studies and identified 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 The T2FMM was identified in 14/186 (8%) of MRI studies, 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 < .00001). In oligodendrogliomas with T2FMM, IDH1‐mutations or specific differentially expressed genes were not identified. Conclusion and Clinical Importance The T2FMM can be readily identified on routinely obtained MRI sequences. It is a specific biomarker for oligodendroglioma in dogs, and was significantly associated with non‐enhancing LGO.

An Illustrated Scoping Review of the Magnetic Resonance Imaging Characteristics of Canine and Feline Brain Tumors

“…The infarct is heterogeneously iso-to hypointense on T2*GRE, is rin hancing, associated with significant mass effect, and demonstrates T2W blackout (lesion hypoi sity on DWI and ADC) due to susceptibility effects of hemorrhage. On DWI and ADC image peripheral hyperintensity surrounding the hypointense lesion core represents perilesional ede The primary neoplastic differential diagnostic considerations for solitary intramasses are neuroepithelial tumors, among which oligodendrogliomas and astrocyto (i.e., gliomas) predominate in the dog (Figure 5, Cases 16-20), with other uncommo rare possible differentials including undefined glioma (oligoastrocytoma), brain met sis, ependymoma, lymphoma, HS, and embryonal tumors [2,9,10,31,32,55,[66][67][68][69][70][71][72][73][74][75][76][77][78][79][80]. Glio can have wide-ranging MRI appearances, resulting in imaging features that may ove substantially with brain abscesses, ischemic and hemorrhagic brain infarctions, fu granulomas, immune-mediated encephalitides, leukoencephalopathies, and meningi [2,[6][7][8]10,[12][13][14]67,77,78].…”

“…The primary neoplastic differential diagnostic considerations for solitary intra-axial masses are neuroepithelial tumors, among which oligodendrogliomas and astrocytomas (i.e., gliomas) predominate in the dog (Figure 5, Cases 16-20), with other uncommon to rare possible differentials including undefined glioma (oligoastrocytoma), brain metastasis, ependymoma, lymphoma, HS, and embryonal tumors [2,9,10,31,32,55,[66][67][68][69][70][71][72][73][74][75][76][77][78][79][80]. Gliomas can have wide-ranging MRI appearances, resulting in imaging features that may overlap substantially with brain abscesses, ischemic and hemorrhagic brain infarctions, fungal granulomas, immune-mediated encephalitides, leukoencephalopathies, and meningioma [2,[6][7][8]10,[12][13][14]67,77,78].…”

“…Neoplasms, granulomas, and meningoencephalitides are not usually associated with restricted diffusion and typically demonstrate lesion hyperintensity on T2W, DWI, and ADC images (Figure 5, Case 20), a DWI phenomenon termed T2 shine-through [6,8,35,37,66]. However, in the presence of vasogenic edema, these diseases may demonstrate T2 wash out, which appears as lesion hyperintensity on T2W and ADC images, but lesion isointensity on DWI.…”

“…The inherent MRI features and signal intensities for gliomas are generally non-specific for neoplasia or for individual tumor type or grade [6][7][8]11,70,74,[77][78][79][80]. The majority of gliomas have been documented in the forebrain, although gliomas of any type may occur anywhere in the brain parenchyma [2,70,74,[77][78][79][80], and 60-89% of canine gliomas are highgrade tumors [66,69,70,77,78,80]. Gliomas, as well as other intra-axial neoplasms, are often T1W hypo-to isointense and T2W/FLAIR hyperintense (Figure 5a), but heteregeneous signal intensities are common [2,[7][8][9][10][11]31,32,70,71,77,78].…”

“…Signal heterogeneity may arise from the presence of intratumoral cysts or hemorrhage, which occur in 30-80% and 25-50% of canine gliomas, respectively [2,10,66,69,70,74,[77][78][79][80]. Some degree of mass effect and peritumoral edema are features present in ~90% of gliomas [2,[7][8][9][10][11]66,69,70,74,[77][78][79][80]. However, intra-axial tumors are more likely to be associated with perilesional edema and mass effect than ischemic infarctions [8].…”