Histology of fibrous dysplasia: Osteoid trabeculae that are narrow, curvilinear or irregularly-shaped are arranged haphazardly in a background of dense fibroblastic stroma. The bony trabeculae are immature, inadequately mineralized and lack osteoblastic rimming. In fibrous dysplasia, the immature woven bone is not transformed into lamellar bone due to maturation defect. The trabeculae may show reversal lines similar to those seen in Pagetís disease. A chondroid component is present in about 10% of cases and may be strikingly prominent in rare cases. Areas of cystic change with lipid-laden macrophages and multinucleated giant cells may be present.