Hypofractionated palliative-intent radiation therapy for a postsurgical recurrent grade II cervical spinal meningioma in a dog.

A 10-year-old spayed female golden retriever was referred with clinical signs of spinal cord disease. The dog had a 2-month history of progressive ambulatory tetraparesis, ataxia, and proprioceptive deficits that were confirmed on clinical examination. Magnetic resonance images revealed a compressive intradural-extramedullary mass at C4 to C5. A cervical hemilaminectomy with marginal excision was completed. Initial histopathological assessment suggested metastatic carcinoma, but further immunohistochemical analysis and lack of a primary tumor on CT imaging led to a revised diagnosis of a grade II metaplastic meningioma. The dog experienced rapid tumor regrowth (confirmed on CT imaging 54 d after surgery) and neurological deterioration. Despite palliative-intent radiation therapy (5 Gy weekly for 4 wk), the dog was euthanized 159 d after MRI diagnosis. Necropsy confirmed a persistent grade II meningioma with increased mitotic activity post-irradiation. We present the first report of a canine grade II spinal meningioma treated with a palliative-intent radiation protocol. The tumor's rapid regrowth and limited response suggest that higher doses of radiation or stereotactic radiation protocols may warrant consideration for grades II or III spinal meningiomas. In addition, there may be potential need for early initiation of adjuvant therapy in these high-grade meningiomas. Key clinical message: Metastatic carcinoma in the spinal cord is rare; therefore, metaplastic meningioma should be considered as a differential diagnosis given its atypical architecture on histopathology.