Meningeal osteosarcoma in a dog

A meningeal osteosarcoma was diagnosed in a dog displaying neurologic signs compatible with a space-occupying cerebellar lesion. Gross lesions, restri cted to the brain, consisted of a solitary, compressive mass attached to th e dura mater overlying the left cerebellum. The mass was composed of single and multinucleated, atypical polygonal cells that lined or rested within l acuna surrounded by eosinophilic, mineralized matrix. The matrical componen t stained dark green-yellow to blue with Movat's pentachrome stain, deep bl ue to red with Heidenhain aniline blue stain, and brown-black with Von Koss a stain. Results of these stains were interpreted as tumor osteoid. Foci of dural mineralization and osseous metaplasia were present at the point of t umor attachment. The microscopic observations were interpreted as an osteos arcoma of extraskeletal origin. To our knowledge, these findings represent the first documented case of a meningeal osteosarcoma in a domestic animal species.