In the major text-books on bone pathology, fibrous dysplasia (FD) is regarded as a non-neoplastic process. It is included in the chapter on conditions that simulate a bone neoplasm and it is defined elsewhere as a dysplastic disorder of bone.

Unknown

Microscopically, irregular trabeculae of woven bone are embedded in a moderately cellular fibrous matrix. The bony trabeculae have variable and irregular shapes. Osteoblastic rimming of the trabeculae is characteristically inconspicuous and some of the trabeculae seem to emerge from the surrounding fibrous background, suggesting a metaplastic process. Benign lesions that histologically can be confused with FD are osteofibrous dysplasia of long bones and desmoplastic fibroma. Cases of FD with extensive cartilaginous differentiation may be mistaken histologically or radiologically for a benign chondroblastic tumor, although the adjacent fibro-osseous component allows this distinction. The most important differential diagnosis of FD is with low grade (well-differentiated) central osteosarcoma. Rarely sarcomas can arise in FD and some of them occur in patients that had received radiation therapy (post-radiation sarcomas) .

It should be conservative

Clonal chromosome aberrations have been reported in 8 out of eleven cases of FD in which chromosomal analysis has been performed, suggesting that this entity is of a neoplastic nature. The only recurrent changes described so far in FD have been structural 12p13 aberrations (3 cases) and trisomy 2 (3 cases).