[Fibrous dysplasia versus osteofibrous dysplasia. Morphological, differential diagnostic and clinical aspects. Experiences from the Westfalen bone tumor registry].

Histologically, this lesion, which was first described by Campanacci, is characterized by an osteofibrous stroma replacing normal bone, showing trabeculae which, unlike in FD, are surrounded by a regular rim of prominent cubic osteoblasts, mature lamellar bone and zonal segmentation with newly formed trabeculae mostly in the cortical region. Radiologic features are eccentric, usually diaphyseally localized osteolytic lesions of the tibia with ground glass appearance. Differential diagnosis includes FD and adamantinoma. Just like OFD, the latter occurs almost exclusively in the tibia, its potential malignancy calling for a more radical therapeutical procedure. Being such a rare lesion, there are no clear guidelines regarding formal pathogenesis and therapy of adamantinoma in combination with osteofibrous stromal reaction. The mean age of the eleven patients with OFD was nine years, which is considerably lower than that of patients with FD (30 years). The lesions were found exclusively in the tibia. Surgical therapy is often followed by a recurrence of the tumor (in two cases in the present material), so it should be avoided, where possible. Thus, surgery should only be performed if complications are imminent, such as marked bone deformation or pseudoarthrosis. Unlike in FD, once bone maturation is completed, surgical treatment of OFD is not normally followed by recurrent disease. Thus, the prognosis of OFD with restricted surgical therapy is more favourable than that of FD, which frequently shows extensive skeletal involvement and recurrent disease even after many years. The more aggressive course of OFD reported by other authors must therefore be explained by too early surgical intervention, i.e. during bone maturation.