Optic neuritis and meningoencephalitis associated with an ovarian teratoma in a dog.

A 3-year-old intact female Pit Bull Terrier mix-breed dog was examined because of acute vision loss. Ophthalmologic examination was consistent with bilateral optic neuritis. Abnormalities were not detected on the remainder of the neurological examination. Brain MRI identified multifocal lesions involving the optic nerves and cortical gray matter, while cerebrospinal fluid analysis demonstrated mixed pleocytosis. Abdominal ultrasonography revealed a cystic ovarian mass. Ovariohysterectomy was performed and histopathologic examination was consistent with an ovarian teratoma. Neural tissue within the teratoma featured extensive perivascular cuffing and immunohistochemistry confirmed mixed lymphocytic infiltration. After tumor resection, the dog was treated with corticosteroid for 40 days, leading to resolution of pleocytosis. Vision was preserved in the left eye but there was persistent vision loss in the right eye. Three years after initial presentation, good quality of life with no behavioral evidence of neurological disease or relapse was reported. This case highlights a suspected paraneoplastic neurological syndrome associated with an ovarian teratoma.