Cytologic and Histologic Features of Oligodendrogliomas in Three Dogs

To the authors' knowledge, this is the first canine oligodendroglioma case series to document the high-field magnetic resonance imaging (MRI) findings along with Wright-Giemsa stained intraoperative cytology findings, coupled with H&E and immunohistochemistry, and interpreted under the 2018 Comparative Brain Tumor Consortium (CBTC) criteria. All dogs in this case series presented with a history of chronic seizures. MRI findings for all cranial masses were T1 hypointense to isointense (Case 3) and T2 hyperintense. Cytologic characteristics of all cases included neoplastic cells haphazardly arranged in aggregates, embedded in an extracellular pink fibrillar to mucoid appearing matrix, and often associated with capillaries. Histologically, Case 1 (high-grade) and 3 (low-grade) had an oligodendroglioma morphology, while Case 2 had an undefined morphology. All cases were strongly immunoreactive to Olig2. Cases 1 and 2 were strongly immunoreactive to CNPase and had robust immunoreactivity to GFAP. This case series highlights that Wright-Giemsa intra-operative squash preparations stain can support a presumptive diagnosis of oligodendroglioma.