[Fibrous bone dysplasia and ossifying bone fibroma in the orbital and periorbital region with special reference to CT].

Fibro-osseous conditions affecting the craniofacial bones pose a complex diagnostic problem. Differentiation between monostotic fibrous dysplasia (FD) and ossifying fibroma (OF) is only possible by correlation of clinical, radiographical and histopathological features. CT was superior to conventional radiography/polytomography in defining exact extent and site of lesions and additional lesions, in verifying aetiology of secondary complications, as well as in depicting lesions and tandem-lesions simulating FD and OF. Density of fibro-osseous conditions was variable due to the ratio of fibrous stroma and metaplastic bone present. Density measurements in FD were 32-695 HU, in immature types of OF, consisting mainly of fibrous and osteoid tissue, 30-250 HU and could reach 690 HU in mature OF, but were definitively lower than normal bone in all our cases. Focal intrinsic nonhomogeneity was more significant in mixed types of FD and immature OF.