Board Review Questions of the Week – Bone Tumors

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This week’s case-based question:


A 44-year-old female with no significant medical history presents after sustaining a fall in her home approximately 1 hour ago. She was walking across her kitchen floor when she suddenly slipped and fell. She had to call her son to come downstairs and help her get up after not being able to stand on her own. She says she feels a sharp pain in her left hip and describes the pain intensity of 8 on a scale of 10 and says it does not radiate. She says she is not able to bear any weight on the left side. Her vital signs are as follows: blood pressure 142/82 mm Hg; pulse 105 beats/minute; respirations 20 breaths/minute, and temperature is within normal limits. On physical examination, the left leg is externally rotated but not shortened and point tenderness is prominent on the lateral aspect of the left hip. There is also evidence of swelling and redness surrounding the left hip. Laboratory results are significant for hypercalcemia (11.4 mg/dL). All other labs are within normal limits.

Bone Tumors Q03 – Discuss the differential diagnosis of large lytic lesions of bone

An x-ray of the hip is depicted below:

Biopsy of the lesion reveals malignant fibroblasts and collagen.

What is the most likely diagnosis?

Answer Options

fracture of the hip
fibrosarcoma
osteoid osteoma
Paget’s disease
Ewing sarcoma

And the answer is …


Correct Answer:

fibrosarcoma

Educational Objective:

Discuss the differential diagnosis of large lytic lesions of bone.

Key Point:

Fibrosarcoma may present as a primary bone tumor.

Explanation:

Fibrosarcoma is a malignant tumor derived from mesenchymal cells and is comprised of malignant fibroblasts in a collagen background. It may present as a soft tissue mass or a primary bone tumor. As a primary bone tumor, it has a characteristic radiographic appearance of a “moth-eaten” lytic bone lesion that extends into the surrounding soft tissues. It may present with pain that worsens over time or as an acute, painful episode accompanied by a pathological fracture. Fibrosarcomas may also be found incidentally on imaging studies. A biopsy will reveal malignant fibroblasts in a collagen matrix. Interestingly, the hypercalcemia is likely to be due to ectopic production of parathyroid hormone produced by the tumor.

While this patient most likely has a fracture of the hip, it is not the underlying cause of her presentation and, therefore, not the best answer. An osteoid osteoma is a benign bone tumor most commonly found in young patients. Moreover, the presence of malignant cells on biopsy rules this out as a possible diagnosis. Paget’s disease of the bone is a chronic disorder that can produce excessively thickened, enlarged, and misshapen bones. It does not produce the appearance of lytic lesions and does not have malignant cells on biopsy. Ewing sarcoma is a rare malignant tumor usually diagnosed in young patients. It produces the characteristic “onion-skin” periosteal elevation on x-ray.

References:

Antonescu CR, Erlandson RA, Huvos AG. Primary fibrosarcoma and malignant fibrous histiocytoma of bone–a comparative ultrastructural study: evidence of a spectrum of fibroblastic differentiation. Ultrastructural Pathology. Mar-Apr 2000;24(2):83-91.

Inwards CY, Unni KK. Classification and grading of bone sarcomas. Hematology Oncology Clinics of North America. Jun 1995;9(3):545-69.

Ferri FF. Fibrosarcoma and Liposarcoma. Ferri’s Clinical Advisor. 2017; 188-189

Hogendoom PC, Dei Tox AP. Malignant fibrous histiocytoma and fibrosarcoma of bone: a re-assessment in light of currently employed morphological, immune-histochemical and molecular approaches. Virchows Archiv. 2012; 461: 561-570

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