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Presented by Edward McCarthy, M.D. and prepared by Orin Buetens, M.D.
Case 5: This 5cm mass developed in the tail of the pancreas.
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Week 14: Case 5
A 63 year-old woman had long-standing fibrous dysplasia involving her tibia. Many years previously she had radiation to the proximal tibia.
Correct
Answer: Osteosarcoma
Histology: Radiographic examination shows changes typical of fibrous dysplasia within the distal portion of the tibia. However, proximally, there is a destructive and expansile zone with marked radiodensity in the center of the radiolytic zone. Histologically, there is a cellular spindle cell proliferation within the proximal portion of the tibia. There is extreme cellular atypia and many abnormal mitotic figures. Associated with this sarcomatous area are areas of osteoid production. The osteoid is distributed throughout the lesion in varying densities. The osteoid is directly associated with the sarcomatous tissue. This combination is consistent with osteosarcoma.
Discussion: In this setting, the osteosarcoma is best regarded as a post-radiation sarcoma. There is no evidence of a direct transformation of fibrous dysplasia to osteosarcoma in this case. Fibrous dysplasia, by contrast, may show cellular fibrous tissue with osteoid production. However, bizarre, pleomorphic cells with atypical mitotic figures are not a feature of fibrous dysplasia. Malignant fibrous histiocytoma may also be a histologic expression of a post radiation sarcoma. However, the presence of neoplastic osteoid through the tissue indicates osteosarcomatous differentiation.
Incorrect
Answer: Osteosarcoma
Histology: Radiographic examination shows changes typical of fibrous dysplasia within the distal portion of the tibia. However, proximally, there is a destructive and expansile zone with marked radiodensity in the center of the radiolytic zone. Histologically, there is a cellular spindle cell proliferation within the proximal portion of the tibia. There is extreme cellular atypia and many abnormal mitotic figures. Associated with this sarcomatous area are areas of osteoid production. The osteoid is distributed throughout the lesion in varying densities. The osteoid is directly associated with the sarcomatous tissue. This combination is consistent with osteosarcoma.
Discussion: In this setting, the osteosarcoma is best regarded as a post-radiation sarcoma. There is no evidence of a direct transformation of fibrous dysplasia to osteosarcoma in this case. Fibrous dysplasia, by contrast, may show cellular fibrous tissue with osteoid production. However, bizarre, pleomorphic cells with atypical mitotic figures are not a feature of fibrous dysplasia. Malignant fibrous histiocytoma may also be a histologic expression of a post radiation sarcoma. However, the presence of neoplastic osteoid through the tissue indicates osteosarcomatous differentiation.
