Figure 3

Representative histological images of FD. A) Calvarial FD lesions are characterized by uninterrupted networks of bone trabeculae (b) embedded in the fibrous tissue (ft). B) In FD lesions from gnathic bones, newly formed bone trabeculae (b) are deposited within the fibrous tissue (ft) in a typical discontinuous and parallel pattern. C) Collagen fibers perpendicularly oriented to forming bone surfaces (Sharpey fibers, arrows) represent a recurrent histological feature of FD at all skeletal sites. D-E) Osteomalacic changes and FGF23 production in FD. D) In many cases of FD, processing for undecalcified embedding reveals excess osteoid (asterisks) and severe undermineralization of the fibrous dysplastic bone. E) The mineralization defect of the FD tissue is related to elevated levels of FGF23 produced by activated FD osteogenic cells (arrows), as shown by in situ hybridization.