The anterior proximal tibial diaphysis shows a mildly expansile lucent lesion with well-defined mildly sclerotic borders measuring approximately 6 cm. There is a pathologic fracture through the lesion along with a posterior angulation deformity. Minimal periosteal reaction along the medial aspect of the fracture is noted.
The corresponding histology to this lesion shows so-called Chinese letter trabeculae of immature bone with intervening loose fibrous stroma. These features bear a strong resemblance to fibrous dysplasia.
Unlike fibrous dysplasia, however, there marked rimming of the osteoid by plump osteoblasts.
Osteofibrous dysplasia (ossifying fibromai), a variant of fibrous dysplasia, arises predominantly in the cortex of the tibia in children and adolescents younger than 15. In contrast, fibrous dysplasia arises in the medulla and has a wider anatomic and age distribution, arising in the long bones as well as craniofacial bones and ribs and affecting children and young adults of all ages (Fletcher, Folpe).
Imaging shows a variably radiolucent and sclerotic lesion confined to the cortex. The lesion is enlongated (tracking down the tibia) and in some cases, can be circumferential.
Histologically, it is composed of a spindled proliferation with formation of woven bone. There is prominent osteoblastic rimming (unlike fibrous dysplasia in which osteoblastic rimming is minimal). Scattered and sometimes clustered osteoclasts can be seen. There is a zonal architecture to the lesion -- with the center of the lesion being more cellular and spindled and the islands of bone increasingly more numerous and more mature as one moves peripherally to the tumor edge where the lamellar bone merges with the cortical bone (or the sclerotic bone terminates sharply against the medullary aspect).
Trisomy 7,8,12 and 21 have been detected in a subset of cases, supporting their clonal natures. However, activating mutations of the GNASI gene (common in fibrous dysplasia) are not present. Thus, despite their similar histologic picture, fibrous dysplasia and osteofibrous dysplasia are pathogenetically distinct lesions (Rosai).
In the vast majority of cases (95%), osteofibrous dysplasia affects children younger than 15. The most common location is the anterior aspect of the tibia. Pain and swelling are common presentations. Deformity (bowing) of the tibia can be a complication (Folpe).
Involvement of the fibula can occur in a minority of cases. Cases arising other bones (i.e. ulna, radius) have been documented, but are extremely rare.
Benign self-limited condition that tends to regress after puberty. In rare instances, osteofibrous dysplasia have progressed to adamantinoma, suggesting an association between the two entities (Folpe).
→Osteofibrous dysplasia differs from fibrous dysplasia in the following ways:
→Osteofibrous dysplasia can progress to adamantinoma, suggesting a relationship between the two entities.
Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 1638.
Folpe AL, Inwards CY. Bone and Soft Tissue Pathology: Foundations in Diagnostic Pathology Philadelphia, PA: Elsevier; 2010: 424-428.
Rosai, J. Rosai and Ackerman's Surgical Pathology. 9th Ed. Philadelphia, PA: Elsevier; 2004: 2194.