Age/sex: 2-year-old female
Size: 14.9 x 5.0 x 2.9 cm
The tibia is bent slightly in its mid-portion next to two tan-colored nodules (arrows). The white areas are normal bone marrow. The lesion was initially treated by curettage but recurred two years later as a fracture, at which time the finger was resected.
Fibrous dysplasia
Fibrous dysplasia is a rare condition in which normal bone and bone marrow are replaced by fibrous tissue. The abnormality appears to be related to a mutation of a gene on chromosome 20, leading to impaired proliferation and differentiation of osteoblasts (bone-producing cells). Although these cells produce collagen, the bony trabeculae (or spindles) that develop from this collagen are thinner and weaker than normal. The mutation is thought to occur after fertilization (somatic mutation); thus, it is not inherited.
The disease can occur in a single focus (monostotic) or in multiple bones (polyostotic). Most lesions appear during childhood and early adolescence. Because the foci of fibrous tissue are weaker than the bone they replace, bending (bowing) of the legs or fractures are common clinical manifestations. Involvement of the spine can result in scoliosis.
Below: Radiograph showing femoral bowing (bending) and abnormal bone composition in a 40 year old female patient with polyostotic fibrous dysplasia.
Source: Di Muzio, B. (2010). Fibrous dysplasia - polyostic form. Radiopaedia. https://radiopaedia.org/cases/12166/studies/12502?lang=us
