osseous and chondromatous tumor ossifying fibroma MPATH:572 Ossifying fibromas are benign tumors derived from pluripotential mesenchymal stem cells or osteoblasts. Occur spontaneously or in response to radiation. Preferentially located in mandible, maxilla and caudal spine. Composed of a characteristically regular trabecular bone pattern embedded in a fibrous stroma. Proliferating component consists of spindle cells which give rise to cuboidal osteoblasts to form rounded bodies or trabeculae. Bone trabeculae resemble the alphabet soup shapes characteristic of fibrous dysplasia in humans. In contrast to fibrous dysplasia the bone trabeculae of ossifying fibroma are mostly lamellar and ringed by active osteoblasts. mouse_pathology.ontology