Clinical, imaging and histopathological features of concurrent malignancies in a dog: Meningoencephalitis of unknown origin and a malignant parotid gland carcinoma

Parotid gland tumours are rare in dogs. In this report, a 7-year-old, female, spayed bearded collie was presented for a subacute onset of neurological signs. A meningoencephalitis of unknown origin affecting the cerebellum diagnosed 10 months before had successfully been treated with prednisolone and mycophenolate mofetil. Head CT and MRI showed a right-sided retropharyngeal mass invading the caudal fossa and compressing the cerebellum and brainstem, adjacent to a second lesion involving the right parotid gland. Postmortem examination revealed a malignant parotid gland carcinoma with intracranial extension, occipital bone infiltration and metastasis to the lungs and the right medial retropharyngeal lymph node. The cerebellum was unremarkable. This is the first report describing detailed imaging features of a malignant parotid gland carcinoma developed in a dog previously diagnosed with a meningoencephalitis of unknown origin.