Bone & Soft Tissue Pathology: Cases, Tumors, OmpathStudy

MOUNT KENYA UNIVERSITY — SCHOOL OF MEDICINE Unit: Bone and Soft Tissue Pathology Assessment: CAT 1 — Semester III, 2026 --- Q1. 17-year-old boy, progressive knee pain/swelling ×3 months, night pain, mixed lytic-blastic lesion in metaphysis of distal femur, periosteal elevation (triangular shadow). A. Ewing sarcoma B. Osteosarcoma C. Chondrosarcoma D. Osteoid osteoma E. Osteochondroma Answer: B — Osteosarcoma Codman triangle + mixed lytic/blastic metaphyseal lesion in an adolescent is classic osteosarcoma. Q2. 12-year-old, fever, bone pain, malaise, leukocytosis, lytic femoral lesion with "onion-skin" periosteal reaction. A. Osteomyelitis B. Osteosarcoma C. Ewing sarcoma D. Chondroma E. Liposarcoma Answer: C — Ewing sarcoma Onion-skin lamellated periosteal reaction + systemic symptoms in a child is the classic picture. Q3. 65-year-old man, hip pain worse on weight-bearing, chronic corticosteroid use, subchondral collapse of femoral head. A. Osteoarthritis B. Osteomyelitis C. Osteonecrosis D. Metastasis E. Chondrosarcoma Answer: C — Osteonecrosis Steroid use is a major risk factor; subchondral collapse ("crescent sign") is diagnostic. Q4. 25-year-old athlete, worsening tibial pain with training, small incomplete fracture, no displacement. A. Pathological fracture B. Stress fracture C. Greenstick fracture D. Comminuted fracture E. Compound fracture Answer: B — Stress fracture Repetitive microtrauma from overuse, not a single injury. Q5. Open tibial fracture, persistent discharge/pain, dead bone surrounded by new bone. A. Involucrum and sequestrum B. Sequestrum and involucrum C. Callus and osteoid D. Necrosis and fibrosis E. Granulation tissue and cartilage Answer: B — Sequestrum and involucrum Sequestrum = dead bone; involucrum = live reactive bone shell around it. Q6. 30-year-old man, severe nocturnal bone pain relieved by NSAIDs, small radiolucent nidus in femoral cortex with sclerosis. A. Osteoblastoma B. Osteoid osteoma C. Osteosarcoma D. Ewing sarcoma E. Chondroma Answer: B — Osteoid osteoma Night pain dramatically relieved by NSAIDs + small (<1.5 cm) nidus is pathognomonic. Q7. 50-year-old woman, painless thigh mass that grows rapidly and invades surrounding tissue. A. Lipoma B. Fibroma C. Liposarcoma D. Hemangioma E. Neurofibroma Answer: C — Liposarcoma Rapid growth and local invasion signal malignant transformation. Q8. 40-year-old man, chronic bone pain, intermittent fever, sequestrum + involucrum. A. Acute osteomyelitis B. Chronic osteomyelitis C. Tuberculosis D. Osteosarcoma E. Osteonecrosis Answer: B — Chronic osteomyelitis Sequestrum/involucrum formation is the hallmark of the chronic form. Q9. 15-year-old, painful bone tumour, fever, raised ESR, small round blue cells, t(11;22). A. Osteosarcoma B. Ewing sarcoma C. Lymphoma D. Chondrosarcoma E. Fibrosarcoma Answer: B — Ewing sarcoma t(11;22) → EWSR1-FLI1 fusion is diagnostic. Q10. Fracture fails to heal, cavity lined by synovial-like cells. A. Delayed union B. Non-union C. Pseudoarthrosis D. Osteonecrosis E. Ankylosis Answer: C — Pseudoarthrosis A "false joint" with synovial-like lining forms after failed union. Q11. 70-year-old man, prostate cancer, back pain, dense sclerotic vertebral lesions. A. Osteoclast activation B. Osteoblast stimulation C. Direct tumour necrosis D. Fibrosis E. Cartilage formation Answer: B — Osteoblast stimulation Prostate cancer classically causes osteoblastic (sclerotic) metastases. Q12. Young adult, painless bony projection near knee, cartilage-capped, continuous with medullary cavity. A. Osteosarcoma B. Osteochondroma C. Chondroma D. Fibroma E. Lipoma Answer: B — Osteochondroma Most common benign bone tumour; continuity with medullary cavity is key. Q13. Acute bone pain, fever, swelling, blood culture grows Staph aureus. A. Osteoarthritis B. Osteomyelitis C. Rheumatoid arthritis D. Osteosarcoma E. Gout Answer: B — Osteomyelitis S. aureus is the most common causative organism. Q14. 45-year-old, pelvic mass, cartilage-producing tumour with calcifications and cortical destruction. A. Osteosarcoma B. Chondroma C. Chondrosarcoma D. Liposarcoma E. Fibrosarcoma Answer: C — Chondrosarcoma Cortical destruction = malignant behaviour of a cartilage-forming tumour, typically pelvis/axial skeleton in older adults. Q15. Fracture after minimal trauma, underlying bone tumour on imaging. A. Stress fracture B. Pathological fracture C. Compound fracture D. Greenstick fracture E. Spiral fracture Answer: B — Pathological fracture Occurs through bone weakened by disease. Q16. 10-year-old, osteomyelitis at metaphysis of long bone — why this site? A. Poor blood supply B. Rich vascular supply C. Cartilage weakness D. High calcium content E. Bone density Answer: B — Rich vascular supply Sluggish capillary loops in the metaphysis favour bacterial seeding. Q17. Chronic osteomyelitis → systemic complication with renal dysfunction from protein deposition. A. Osteoporosis B. Amyloidosis C. Fibrosis D. Calcification E. Hyperplasia Answer: B — Amyloi