1. Musculoskeletal system SYLLABUS: RBP(Robbins Basic Pathology) Chapters: TheMusculoskeletal System

2. Musculoskeletal system 56 Chondroma 57 Chondrosarcoma 58 Osteoma 60 Ostosarcoma 187 Aneurysmal bone cyst 189 Eosinophilic granuloma

3. Chondroma - well circumscribed nodules of cartilage - hyaline matrix - cytologically benign neoplastic chondrocytes residing in lacunae

4. Chondroma

5. Chondroma

6. Chondrosarcoma - sheets or ill-defined nodules of cartilage with variable nuclear atypia (enlarged, pleomorphic, hyperchromatic nuclei) - sometimes two or more nuclei per lacuna - invasion of trabecular bone - soft tissue lesions usually with abundant myxoid stroma or spindle cells

7. Chondrosarcoma

8. Chondrosarcoma

9. Osteoma -dense, mature, lamellar bone

10. Osteoma

11. Osteoma

12. Ostosarcoma - minimal diagnostic requirement is malignant calcified osteoid - cytologic malignant features include enlarged, hyperchromatic, pleomorphic, mitotically active nuclei, possibly atypical mitoses - architecture extremely variable: - sheets of osteoid with osteoblast lacunae and little fibrous stroma - thin osteoid trabeculae and more stroma - rare foci of osteoid in irregular islands or rosettes - may have cartilage, and giant cells

13. Ostosarcoma

14. Ostosarcoma

15. Aneurysmal bone cyst (ABC) Probably rather a degenerative change that can occur in many lesions than an independent lesion. About half of cases have areas of precursor lesion (wide variety). - multiple blood filled lakes - fibrous and bony septa - many giant cells often in a row beneath the surface - no cytologic atypia - foci of osteoid and bone

16. Aneurysmal bone cyst

17. Aneurysmal bone cyst

18. Eosinophilic granuloma (Langerhans' cell histiocytosis of bone, Histiocytosis X) - a variety of cell types, but only Langerhans' cell is diagnostic - number of Langerhans' cells present is variable - prototypical Langerhans' cells have abundant, powdery, eosinophilic cytoplasm and characteristic bean-shaped nuclei with grooves and indentations, may or may not have well-demarcated cell borders - variable numbers of ordinary histiocytes and sometimes foam cells - common secondary components include eosinophils, may form aggregates surrounded by histiocytes and Langerhans' cells, neutrophils, lymphocytes and plasma cells

19. Eosinophilic granuloma

20. Eosinophilic granuloma