1. Bone island (enostosis) —ovoid with long axis parallel to long axis of bone and a feathered border.
2. Enchondroma —confluent punctate or nodular calcification, denser centrally than peripherally. Enchondromas in the large long bones are often more calcified than those in the fingers.
3. Metastasis —prostate, breast, mucinous adenocarcinoma of GI tract, carcinoid, lymphoma, TCC in adults. Medulloblastoma and neuroblastoma in children.
4. Callus —usually associated with a fusiform swelling in long bones.
5. Bone infarct —usually a central metadiaphyseal lucency with thin serpentine calcified margins.
6. Paget’s disease —blastic phase causes sclerosis accompanied by bone expansion, and cortical and trabecular thickening.
7. Osteoma —arises from membranous bone: skull and paranasal sinuses. Ivory osteomas contain no trabeculae. Mature osteomas have visible marrow. If multiple consider Gardner syndrome.
8. Osteoid osteoma/osteoblastoma —sclerosis caused by eccentric periosteal thickening. Osteoid osteoma: radiolucent nidus <2 cm. Osteoblastoma: more common in the posterior elements of spine, larger nidus with thin shell.
9. Healed or healing bone lesion —treated metastasis, NOF, simple bone cyst, brown tumour, eosinophilic granuloma.
10. Primary bone sarcoma —aggressive features: poorly defined margins, aggressive periosteal reaction, Codman’s triangles, bone destruction, soft tissue mass.
11. Fibrous dysplasia —usually lytic with ground glass areas but can calcify in later life.
12. Chronic osteomyelitis —usually associated with an area of lysis, chronic periosteal reaction and occasionally a sequestrum.
13. Chronic recurrent multifocal osteomyelitis (CRMO) —idiopathic inflammatory disorder. Most commonly affects clavicles and tibias in children. Often multifocal.
14. Lymphoma —primary bone lymphoma rare. More common as secondary involvement. Large extraosseous soft tissue mass with relative preservation of bone.
15. Cement and bone graft substitutes —history of surgery.