Fibrous dysplasia of the orbital roof
Facial deformity in a teenager.
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Axial CT images of the skull (bone window) revealed an expansile bone lesion with a typical ground glass appearance involving the roof of the right orbit.
Note the mass effect on the ipsilateral frontal sinus and right orbit.
Fibrous dysplasia is a developmental anomaly manifested as a defect in osteoblastic differentiation and maturation. It can affect any bone of the body. The skull and facial bones are the affected sites in 10–25% of patients with monostotic ﬁbrous dysplasia and in 50% of patients with polyostotic ﬁbrous dysplasia.
CT radiological features have three patterns:
- Ground glass pattern (>50%): as in this case.
- Homogeneously dense pattern (~25%).
- Cystic pattern (~20%).
- Brown EW, Megerian CA, McKenna MJ, Weber A. Fibrous dysplasia of the temporal bone. AJR 1995 ;164:679–682 Kumar R, Madewell JE, Lindell MM, Swischuk LE. Fibrous lesions of bones. RadioGraphics 1990 ;10:237–256