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Chapter 19: Soft Tissue and Bone Pathology

A 22-year-old male presents with pain in his lower leg. Plain X-ray demonstrates a lytic lesion in the distal metaphysis of the femur and MRI shows numerous fluid-fluid levels. Histologically, there are blood filled cystic spaces bounded by septae containing stromal cells, multinucleated giant cells and reactive woven bone that in areas has the blue bone appearance. Which of the following is the most likely diagnosis?

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A. Aneurysmal bone cyst

B. Telangiectatic osteosarcoma

C. Giant cell tumor of bone

D. Non-ossifying fibroma

Answer: A

Explanation: The histologic findings and radiologic features described are characteristic for ABC. Although telangiectatic osteosarcomas can show fluid-fluid levels on imaging and blood-filled lakes on histology, the presence of sarcomatous stroma separates it from ABC. Though aneurysmal bone cyst like changes can be seen in a subset of giant cell tumors, the metaphyseal location in this case makes this diagnosis unlikely. The metaphyseal location would fit for a non-ossifying fibroma however these tumors are characterized by bland spindled cells arranged in a storiform growth pattern admixed with osteoclast-like giant cells often with collections of foamy macrophages and hemosiderin deposition.

Which of these tumors are not translocation associated?

A. Synovial sarcoma

B. Alveolar rhabdomyosarcoma

C. Undifferentiated pleomorphic sarcoma

D. Low grade fibromyxoid sarcoma

Answer: C

Explanation: Soft tissue sarcomas can be divided into two groups based on their cytogenetic features; sarcomas with simple cytogenetics consisting of relatively normal chromosomal components with chromosomal translocations or single gene mutations and those with aneuploidy and complex cytogenetic features. Approximately 30% of sarcomas are translocation associated. Synovial sarcoma is characterized by a t(X:18) translocation involving SS18(SYT) gene on chromosome 18 and either SSX1 or the SSX2 gene on chromosome X. Alveolar rhabdomyosarcoma is associated with t(2:13) and less commonly t(1:13) which results in fusion of PAX3 and PAX7 genes, respectively, to the FKHR gene located on 13q14. Low grade fibromyxoid sarcoma is most commonly associated with t(7:16) resulting in FUS-CREB3L2 gene fusion. Undifferentiated pleomorphic sarcoma is characterized by complex cytogenetic features.

A 65-year-old male with a pathologic fracture of the left femur and a large cavitary lung mass. What is your diagnosis?

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A. Chordoma

B. Chondrosarcoma

C. Metastatic adenocarcinoma

D....

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