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Presented by Edward McCarthy, M.D. and prepared by Jon Davison, M.D.
Case 1: An 18 year old man had a lump in his lower leg which was increasing in firmness over the past several months.
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Question 1 of 1
1. Question
Week 208: Case 1
An 18 year old man had a lump in his lower leg which was increasing in firmness over the past several months. A radiograph demonstrated a well defined radiodensity in the back of his knee.images/JMD_1-17-05_SPWC/Case_1/1.jpg
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images/JMD_1-17-05_SPWC/Case_1/4.jpgCorrect
Answer: Heterotopic ossification
Histology: none provided
Discussion: The radiograph shows a well defined radiodense mass. The trabecular pattern of the radiodensity indicates that the lesion is composed of bone. Histologically, there is osteoid deposition in a cellular fibrous tissue stroma. There is a distinct zonal pattern i.e. the bone is more dense at the periphery of the lesion. The central cellular area shows a distinct “tissue culture-like” appearance. Although the stroma is cellular, there is no evidence of pleomorphism or atypical mitotic figures. The lesion is not an osteogenic sarcoma because of the lack of atypia and abnormal mitotic figures. In addition, the zonal pattern is indicative of a non-neoplastic, reactive disorder. Zonal patterns are not present in osteogenic sarcoma. The lesion is not a chondrosarcoma. Although the radiograph may raise the possibility of a cartilage tumor, there is no cartilage in the lesion. The lesion is not tumoral calcinosis because there is no evidence of dystrophic calcification. In this case, the radiodensity is entirely due to bone formation.
Incorrect
Answer: Heterotopic ossification
Histology: none provided
Discussion: The radiograph shows a well defined radiodense mass. The trabecular pattern of the radiodensity indicates that the lesion is composed of bone. Histologically, there is osteoid deposition in a cellular fibrous tissue stroma. There is a distinct zonal pattern i.e. the bone is more dense at the periphery of the lesion. The central cellular area shows a distinct “tissue culture-like” appearance. Although the stroma is cellular, there is no evidence of pleomorphism or atypical mitotic figures. The lesion is not an osteogenic sarcoma because of the lack of atypia and abnormal mitotic figures. In addition, the zonal pattern is indicative of a non-neoplastic, reactive disorder. Zonal patterns are not present in osteogenic sarcoma. The lesion is not a chondrosarcoma. Although the radiograph may raise the possibility of a cartilage tumor, there is no cartilage in the lesion. The lesion is not tumoral calcinosis because there is no evidence of dystrophic calcification. In this case, the radiodensity is entirely due to bone formation.
