Nonossifying fibroma. Electron microscopic examination of two cases supporting a histiocytic rather than a fibroblastic origin.

Nonossifying fibromas appear to be histiocytic lesions. On the basis of light and electron microscopic studies, as well as behavior, they are identical to benign fibrohistiocytomas found in soft tissues. The fibroblastic appearance of some of these lesions by light and electron microscopy, especially in older lesions, reflects the ability of histiocytes to behave as facultative fibroblasts. Final data of the cell of origin for these lesions must await more definitive studies by other methods, perhaps using immunologic, immunoperoxidase and/or surface markers techniques.