Optic Chiasm and Bilateral Optic Nerve Oligodendroglioma in A 29-Month-Old German Shepherd.

Abstract

OBJECTIVE: To report the first documented case of high-grade optic chiasm and nerve oligodendroglioma in a young dog and contribute to the comparative study of gliomas in humans and canines. ANIMAL STUDIED: A 29-month-old male intact German Shepherd. PROCEDURES: Over 2 months, the patient underwent repeated physical and ophthalmic examinations, systemic health assessments (complete blood count, serum biochemistry, urinalysis, and infectious disease testing), anesthetized MRI, ultrasound-guided biopsy of the left retrobulbar mass, and necropsy. Histopathologic and immunohistochemical analyses, including OLIG2 and GFAP immunohistochemistry, were performed. RESULTS: MRI evaluation identified a large, lobulated, asymmetric mass with retrobulbar involvement and compression of the optic chiasm and optic nerves. The mass exhibited hyperintense signals on T2-weighted and T2-FLAIR sequences, mixed intensity on T1-weighted imaging, and heterogeneous contrast enhancement, with areas of necrosis and meningeal enhancement suggestive of an aggressive neoplasm. Gross necropsy findings and histopathologic examination of post-mortem tissues confirmed the diagnosis of a high-grade oligodendroglioma, with tumor cells demonstrating marked nuclear atypia, high mitotic activity, and OLIG2 nuclear immunoreactivity. CONCLUSIONS: The tumor's localization and histological characteristics suggested a primary origin within the optic pathway, differing from typical canine oligodendrogliomas. This case emphasizes the rarity of canine optic pathway oligodendrogliomas, a diagnosis that is similarly uncommon in human medicine. Dogs have been proposed as an intermediate animal model for human gliomas, and this case underscores the need for further molecular characterization of canine gliomas to improve diagnostic accuracy, therapeutic strategies, and comparative oncology insights.