Clinical course and MRI lesion progression over 4 years in a dog with final diagnosis of high‐grade oligodendroglioma

Abstract A 9‐month‐old Cavalier King Charles Spaniel with 3‐month history of paroxysmal episodes of cervical pain and scratching had a magnetic resonance imaging revealing a large intra‐axial cystic lesion in the left frontal lobe, caudal transtentorial and foraminal brain herniation, and cervical syringomyelia. Despite suspected high‐grade glioma, clinical signs improved under palliative treatment. Follow‐up magnetic resonance imaging 2.5 years later showed a similar lesion size, with no radiological evidence of increased intracranial pressure. The differential diagnosis was reconsidered to possibly porencephaly, congenital cystic malformation or parasitic cyst. The dog remained clinically stable for 19 months before developing acute generalised, single, self‐limiting seizures, deteriorating to cluster seizures, stupor, cardiovascular arrest and death. Postmortem magnetic resonance imaging revealed lesion progression with ventricle invasion. Neuropathology confirmed a high‐grade oligodendroglioma with subarachnoid and intraventricular drop metastasis. This is the first report describing long‐term clinical course and magnetic resonance imaging lesion progression under palliative treatment of a dog ultimately diagnosed with high‐grade oligodendroglioma.