Meningeal dissemination of a pituitary carcinoma to the cauda equina in a dog.

An 8-year-old spayed female border collie dog was diagnosed with an invasive pituitary macrotumor. Five months after radiation therapy, the patient developed paraparesis and lumbosacral pain. Necropsy revealed a pituitary carcinoma with cauda equina drop metastasis. In cases of pituitary masses, meningeal dissemination should be considered if neurologic status declines.