PA32.1-7 | Bone & Soft Tissue — Graded Quiz

A 12-year-old boy with sickle cell disease is brought with 5 days of high fever, bone pain, and swelling over the mid-shaft of the tibia. X-ray shows periosteal elevation with underlying bone destruction. Blood culture grows a gram-negative rod. Which organism and mechanism most accurately explain this presentation?

On post-mortem examination of an 8-year-old who died of untreated osteomyelitis, the pathologist identifies a fragment of pale, necrotic cortical bone separated from living bone by a layer of pus and granulation tissue. The remaining bone cortex shows new periosteal bone formation encasing the infected area. Which pair of terms correctly names these two findings?

A 17-year-old boy presents with 6 weeks of worsening right knee pain, worse at night, and an ill-defined soft tissue mass. X-ray shows a metaphyseal lesion with cortical destruction, Codman triangle, and a 'sunburst' pattern. Chest CT shows two 'cannonball' pulmonary nodules. Biopsy confirms osteosarcoma. Which molecular or histological feature distinguishes primary (de novo) osteosarcoma from a secondary osteosarcoma arising in Paget disease?

A pathologist receives a bone biopsy from a 72-year-old man with skull enlargement, elevated serum ALP, and hearing loss. Microscopy shows lamellar bone trabeculae with irregular, prominent cement lines running in multiple directions, creating a mosaic appearance. Active osteoclasts and osteoblasts are seen at the trabecular surface. Which phase of Paget disease is most likely represented, and what is the immediate mechanism of the patient's hearing loss?

A 28-year-old woman undergoes excision of a painless lump from the right posterior thigh. Gross specimen shows a well-circumscribed, yellow, lobulated mass of uniform consistency. Histology shows mature lipocytes with no nuclear atypia, no lipoblasts, and no necrosis. Ki-67 is <1%. One year later, an MRI for a different complaint shows a large heterogeneous retroperitoneal mass in the same patient with areas of myxoid stroma and scattered lipoblasts. The best explanation for the retroperitoneal finding is:

A 24-year-old man undergoes knee arthroscopy for a suspected meniscal tear. Synovial fluid analysis shows: WBC 45,000 cells/µL (80% neutrophils), glucose 28 mg/dL (simultaneous serum 98 mg/dL), protein elevated, Gram stain negative. RF and anti-CCP antibodies are negative. Two weeks earlier he had urethritis treated with azithromycin. The most likely diagnosis, and the pathological basis of the joint inflammation, is:

A 60-year-old obese woman presents with bilateral knee pain for 3 years, worse with activity and at the end of the day. X-rays show joint space narrowing, subchondral sclerosis, and osteophytes. Synovial fluid: WBC 800 cells/µL, predominantly mononuclear. A biopsy of the articular cartilage shows fibrillation, vertical clefts, and loss of chondrocytes in the superficial zone. Serum uric acid is normal; RF is negative. Which underlying mechanism best explains the cartilage destruction in this patient?

A 19-year-old man presents with 3 months of mid-shaft femur pain and a soft tissue mass. X-ray shows a permeative, lytic lesion of the diaphysis with an 'onion-skin' periosteal reaction and no visible bone matrix production. Biopsy shows sheets of uniform small round blue cells with scant cytoplasm. Fluorescence in situ hybridisation (FISH) reveals t(11;22)(q24;q12). The tumor cells are strongly positive for CD99 (MIC2). Which statement about the pathogenesis of this tumor is MOST accurate?

A 40-year-old woman undergoes craniotomy for a parasagittal mass. Histology shows a biphasic pattern of epithelial-like cells lining gland-like spaces and spindle cells in a haemangiopericytoma-like vascular pattern. Immunohistochemistry shows TLE1 positivity. Cytogenetics reveal t(X;18)(p11;q11) producing SS18-SSX2 fusion. Despite the histological appearance, what is the correct cell of origin and the most important clinical implication of this tumor?

A 72-year-old woman presents with progressive bowing of the left femur and tibial enlargement. Serum alkaline phosphatase is 850 U/L (normal <120). Bone biopsy shows: irregular cement lines creating a 'jigsaw puzzle' pattern, osteoclasts with more than 100 nuclei (normal ≤3), and increased fibrous marrow stroma. Three years later she is admitted with sudden-onset severe thigh pain; X-ray shows a lytic lesion in the pagetic femur. Biopsy reveals pleomorphic spindle cells producing osteoid. What is the most feared and most likely complication in this patient, and what is her prognosis?

A 50-year-old woman with a 2-year history of symmetric small joint arthritis (MCP and PIP joints) presents for follow-up. X-rays now show marginal erosions and periarticular osteopenia at the MCPs. Serum anti-CCP antibody titre is 320 U/mL (strongly positive). Synovial biopsy reveals a sheet-like mass of proliferating synoviocytes with underlying plasma cell and lymphocyte infiltrate. She is being considered for biologic therapy. Which cellular process explains why pannus — the tissue seen on biopsy — is the defining lesion of joint destruction in this disease?

A histopathology practicum slide shows a section of bone with the following features: irregular cement lines in lamellar bone creating a mosaic pattern, markedly enlarged osteoclasts with >20 nuclei, prominent fibrovascular stroma between trabeculae, and thickened but structurally disorganised trabeculae. A second slide shows a section of synovial tissue with: marked villous hypertrophy, a dense infiltrate of plasma cells and lymphocytes, germinal centre formation, and fibrin on the surface. Which pairing correctly matches each slide to its disease and its key diagnostic histological feature?