Retrobulbar malignant peripheral nerve sheath tumor in a golden retriever dog: A challenging diagnosis.

A 9-year-old golden retriever dog was diagnosed with a left retrobulbar mass. Fine-needle aspirations and incisional biopsies resulted in discordant diagnoses: myxosarcoma/myxoma or rhadomyosarcoma, respectively. Immunohistochemistry following exenteration allowed definitive diagnosis of malignant peripheral nerve sheath tumor with fibromyxomatous differentiation. Fifteen weeks after surgery, an aggressive recurrence resulted in euthanasia.