[Fibrous dysplasia of the bone. Contribution of nuclear medicine in the diagnosis of suspicion of sarcomatous degeneration].

Fibrous dysplasia (FD) is a relatively frequent benign disease of the bone in which there is a maturation disorder of the bone-forming mesenchyme where the lamellar bone marrow is replaced with abnormal fibrous tissue. Its diagnosis is often an accidental finding when X-ray studies or bone scans are performed for other reasons since it is usually asymptomatic. There may be complications such as deformities, pathological fractures and exceptionally malignant transformation. The differential diagnosis between malignancy and FD can be complicated and lead to late diagnosis when sarcomatous degeneration already exists. In this context, the positron tomography with (18)F-fluorodeoxyglucose (FDG-PET) may be useful in the monitoring of this condition. We present two cases of patients diagnosed of FD with suspicion of malignization of their bone lesions who were referred to Nuclear Medicin.