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

A 10-year-old boy presents with fever, severe pain, and swelling over the distal femur for 2 weeks. X-ray shows periosteal elevation and a lytic lesion in the metaphysis. Blood cultures grow Staphylococcus aureus. Histology of the debrided tissue shows a central area of necrotic bone surrounded by granulation tissue and new periosteal bone formation. What term describes the dead bone fragment visible on the specimen?

A 35-year-old man from a rural area presents with chronic back pain, low-grade fever, and weight loss for 4 months. MRI shows vertebral body destruction at T9-T10 with a paravertebral 'cold abscess' extending along the psoas muscle sheath. Biopsy of the lesion reveals granulomatous inflammation with central caseous necrosis and Langhans giant cells. Which of the following features on gross examination is MOST characteristic of this condition?

A 16-year-old boy presents with a 3-month history of worsening pain and swelling around the right knee. X-ray of the distal femur shows a sunburst periosteal reaction and an ill-defined lytic lesion with Codman triangle in the metaphysis. Biopsy reveals highly pleomorphic spindle cells producing osteoid directly. What is the most likely diagnosis and its defining microscopic feature?

A 22-year-old woman presents with a painless bony swelling at the distal metaphysis of the femur noticed incidentally. X-ray shows a pedunculated bony projection with cortical and medullary continuity with the underlying bone, capped by a radiolucent layer. The lesion has been stable for 2 years. Which statement BEST describes the risk profile and key warning sign for this lesion?

A 25-year-old woman has a 6-month history of dull knee pain. X-ray shows an eccentric, soap-bubble lytic lesion in the epiphysis of the proximal tibia extending to the articular surface. There is no periosteal reaction. Biopsy shows a dual population of mononuclear stromal cells (CD68−) evenly interspersed with numerous osteoclast-like multinucleated giant cells. What is the diagnosis and the most common complication after curettage?

A 14-year-old boy presents with 2 months of progressive pain and a soft tissue mass over the mid-shaft of the femur (diaphysis). X-ray shows a permeative lytic lesion with a lamellated 'onion-skin' periosteal reaction. Biopsy reveals sheets of uniform small round blue cells with scant cytoplasm, arranged in pseudorosettes around central neurofibrils. Cytogenetics confirms a t(11;22)(q24;q12) translocation. Which feature BEST distinguishes this tumour from osteosarcoma?

A 55-year-old man with a known history of carcinoma prostate presents with severe low back pain. Bone scan shows multiple hot spots throughout the axial skeleton. X-ray of the lumbar spine shows areas of increased density (sclerotic lesions). Serum PSA is markedly elevated. Which primary carcinoma is MOST likely to produce osteoblastic (sclerotic) bone metastases compared to osteolytic metastases?

A 52-year-old man presents with an enlarging, deep-seated retroperitoneal mass. CT scan shows a large heterogeneous mass with areas of fat density (−70 to −120 HU) intermixed with soft tissue components and calcification. Biopsy reveals a highly pleomorphic tumour with lipoblasts — cells showing scalloped nuclei indented by large intracytoplasmic fat vacuoles. What is the diagnosis and the MOST important histological prognostic indicator?

A 5-year-old boy is brought with a 4-week history of a rapidly growing mass in the right orbit and proptosis. MRI shows a 4 cm infiltrative mass in the right orbit. Biopsy reveals primitive round to spindle cells with eosinophilic cytoplasm; immunohistochemistry is strongly positive for desmin, MyoD1, and myogenin. Cytogenetics shows t(2;13)(q35;q14) PAX3-FOXO1 fusion. What is the diagnosis and the histological subtype with the WORST prognosis?

A 35-year-old man presents with a slowly growing mass near the right knee. MRI shows a para-articular soft tissue mass with fluid-fluid levels and a dark rim on T2-weighted images, arising close to the synovium of the knee joint. Biopsy shows a biphasic tumour with gland-forming epithelial cells set in a background of spindle cells; immunohistochemistry is positive for EMA, CK7, and TLE1. Molecular analysis confirms SS18-SSX2 fusion. What is the MOST likely diagnosis?

An 80-year-old man is referred for investigation of an elevated serum alkaline phosphatase (ALP) found incidentally on routine blood tests. He is otherwise asymptomatic but recalls having hearing loss and 'hat size increasing' over recent years. X-ray of the skull shows cotton-wool opacities and thickening of the calvarium. X-ray of the tibia shows a sabre-shin deformity with cortical thickening and coarsened, disorganised trabecular pattern. What is the most characteristic histological finding in this condition?

A 50-year-old woman presents with a 2-year history of symmetric pain and stiffness in both hands, worst in the morning for more than 1 hour. Examination shows swelling of the MCP and PIP joints, ulnar deviation of the fingers, and subcutaneous nodules over the elbows. RF is positive, anti-CCP antibody titre is markedly elevated. Synovial biopsy shows villous hypertrophy with a dense infiltrate of lymphocytes and plasma cells, and formation of a proliferating granulation tissue covering and eroding the articular cartilage. What is this tissue called?

A 65-year-old obese man presents with acute onset severe pain, redness, warmth, and swelling in the right first metatarsophalangeal (MTP) joint — a classic podagra attack. Serum uric acid is 9.2 mg/dL. Synovial fluid aspiration is performed. Which of the following correctly describes the synovial fluid finding and distinguishes this condition from pseudogout?