Bone and Soft Tissue Lab

Key questions

1. Q1What does normal adult cancellous bone look like?

   Pink, smooth lamellar trabeculae (parallel layers, flat osteocytes in lacunae) with hematopoietic marrow and fat between them; no woven bone.
2. Q2How do you recognize a growth plate on a slide?

   Hyaline cartilage (pale purple) on one side, columns of chondrocytes, then calcified cartilage cores covered by pink bone (primary spongiosa) on the other.
3. Q3How does chronic osteomyelitis look?

   Marrow replaced by fibrous tissue with lymphocytes and plasma cells beside dead or remodeled bone; in the gross/X-ray, sequestrum wrapped by involucrum.
4. Q4How does fracture callus look?

   A mix of cartilage and haphazard woven bone (irregular, plump, crowded osteocytes, no lamellae) — normal repair, but woven bone in an adult otherwise means disease.
5. Q5How does osteoporosis look grossly?

   Vertebral bodies with thin, sparse trabeculae; a vertebra may be collapsed (compression fracture) so the discs above and below nearly touch.
6. Q6What is the classic Paget image?

   Mosaic (jigsaw) pattern of lamellar bone — irregular blue cement lines between bone fragments — with fibrovascular marrow and big osteoclasts.
7. Q7How do RA and gout appear in the lab?

   RA: hands with MCP swelling and ulnar deviation of the fingers; rheumatoid nodule = central fibrinoid necrosis ringed by palisading macrophages. Gout: tophus = pale amorphous/feathery crystal deposits ringed by macrophages and foreign-body giant cells.

Key questions

1. Q8How does an osteochondroma look?

   X-ray/gross: a bony stalk growing away from the joint, continuous with the cortex and marrow, capped by cartilage. Micro: hyaline cartilage cap (purple) transitioning to cancellous bone (pink) by endochondral ossification.
2. Q9How does an aneurysmal bone cyst look?

   Gross: multiloculated, spongy mass of blood-filled cysts. Micro: cyst walls of fibroblasts, osteoclast-like giant cells, reactive woven bone and red cells. Benign, usually metaphyseal.
3. Q10How does osteosarcoma look?

   Gross: large gray-white, hemorrhagic mass in the metaphysis destroying cortex and lifting periosteum. Micro: pleomorphic malignant cells directly making lace-like osteoid/woven bone.
4. Q11How does chondrosarcoma look?

   Gross: lobulated, glistening gray-blue, bubbly cartilage mass, often hemorrhagic, in pelvis/shoulder. Micro: crowded atypical chondrocytes in lacunae within blue hyaline matrix, invading bone.
5. Q12How does Ewing sarcoma look?

   Gross: gray-white tumor in the diaphysis, spreading in the medulla and cortex. Micro: monotonous sheets of small round blue cells with scant cytoplasm.
6. Q13What features separate benign from malignant bone tumors on images?

   Benign: well-circumscribed, narrow zone of transition, bland cells, maturation (osteochondroma cap → bone). Malignant: destruction of cortex, soft tissue extension, pleomorphism, mitoses, necrosis, tumor cells making matrix directly.

Key questions

1. Q14How does fibromatosis look?

   Long, sweeping bundles of bland fibroblasts with collagen and slit-like vessels that infiltrate between skeletal muscle fibers (the muscle is trapped at the edge).
2. Q15How does a plexiform neurofibroma look grossly?

   A tangle of thickened nerve fascicles — "bag of worms" — essentially diagnostic of NF1.
3. Q16How does liposarcoma look?

   Gross: a large, yellow, fatty, lobulated mass (often deep thigh or retroperitoneum). Micro: fat cells of varying size with fibrous septa, atypical hyperchromatic stromal cells and lipoblasts.
4. Q17What does lymphedema-associated angiosarcoma look like clinically?

   A chronically swollen limb with thickened, discolored skin and red-brown to purple nodules that ulcerate and bleed.
5. Q18What is an intramuscular myxoma?

   A benign tumor within skeletal muscle: gross = white, glistening, gelatinous nodules in muscle; micro = very few bland spindle/stellate cells in abundant pale myxoid matrix with scant vessels. (Its bland, hypovascular look separates it from myxoid liposarcoma, which has lipoblasts and chicken-wire capillaries.)