A case of anaplastic meningioma in a dog. 
A tumor sized in 2.0x2.0x2.5 cm developed in the cerebellum of a female Beagle was pathologically investigated.  Histopathologically, the tumor grew by compression and partially by infiltration into the adjacent cerebellar parenchyma.  There were a large number of necrotic lesions and proliferation of collagen fibers.  The tumor cells had oval nucleus showing cellular atypia and a high mitotic index.  The tumor cells were reacted with vimentin antibody on immunostain.  Electron microscopic examination revealed the tumor cells interdigitated with cytoplasmic processus where the desmosomes developed on cell junction.  This tumor was diagnosed as anaplastic meningioma, which is rarely observed in dogs.