1. Fibrous Dysplasia Fibrous dysplasia is a developmental abnormality in which osteoblasts do not undergo normal differentiation and maturation Approximately 70-80% are monostotic and 20-30% are polyostotic Fibrous dysplasia not uncommonly involves the skull and facial bones, usually the frontal, sphenoid, maxillary and ethmoid bones, although the case presented here involves the occiput Radiographically, mixed radiolucent and sclerotic lesions are seen, often with expansion (arrow) Slide 1 of 3

2. Fibrous Dysplasia Nuclear medicine bone scan may show increased uptake in sites of fibrous dysplasia such as this static image from a three phase bone scan demonstrating increased uptake in the occiput, corresponding to the radiographic abnormality Slide 2 of 3

3. Fibrous Dysplasia Computed tomography (CT) may show the internal fibrous matrix better than conventional radiographs (arrows) Slide 3 of 3