A 20-year-old female presents to your office with a complaint of leg pain and mechanical symptoms. She has recently started running and reports a painful snapping sensation in her leg, and states she can feel a hard mass in her calf. X-ray is shown in Figure 8–7.
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Figure 8–7
What type of lesion is this?
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Chondromyxoid fibroma
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Chondroblastoma
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Pedunculated osteochondroma
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Osteofibrous dysplasia
Discussion
The correct answer is (C). The imaging shows an osteochondroma. Osteochondromas can be either sessile, meaning having a broad origin from the
underlying bone (looks like a mountain) or pedunculated, meaning having a stalk (looks like broccoli). The imaging is characteristic and usually diagnostic. Chondromyxoid fibroma and osteofibrous dysplasia both demonstrate a soap-bubble appearance within the bone, osteofibrous dysplasia is a tibial anterior cortical lesion, whereas CMF is eccentric and displays expansive remodeling. Chondroblastoma is predominantly a radiolucent epiphyseal lesion.
Which of the following imaging characteristics defines this lesion?
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Corticomedullary continuity between host bone and the mass
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Juxtacortical appearance, with mass sitting on top of uninterrupted cortex
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Growth pointing towards the growth plate or joint
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A cartilage cap that grows well after skeletal maturity
Discussion
The correct answer is (A). Osteochondromas are benign bone lesions in which histologically normal bone grows transversely away from the host bone. The lesion grows away from the growth plate or neighboring joint, and is covered with a cartilage cap. If this cap continues to grow after skeletal maturity, malignant transformation is a concern. A key diagnostic characteristic of osteochondroma on imaging studies is the presence of corticomedullary continuity between the underlying bone and the lesion; a juxtacortical appearance where the underlying cortex is uninterrupted or is saucerized is more concerning for parosteal osteosarcoma or other periosteal lesions.
Multiple hereditary exostoses (MHE) is associated with a gene mutation within which loci?
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p53
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NF1
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CD99
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EXT1
Discussion
The correct answer is (D). The EXT1, EXT2, and EXT3 genetic loci are associated with this disorder. They are tumor suppressor genes, and the risk of malignant transformation of one of the osteochondromas is higher in patients with this condition. Mutations in p53 are associated with other malignancies, such as osteosarcoma. NF1 mutations are associated with neurofibromatosis, and CD99 is
associated with Ewing sarcoma.
Which of the following clinical scenarios is most concerning for potential malignant transformation?
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Twelve-year-old male with a similar lesion of lateral distal femur, experiencing popping and snapping during stair-climbing
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Eight-year-old female with enlarging similar lesion of proximal fibula, with radiation of numbness and tingling down anterolateral lower leg
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Forty-five-year-old male with a similar lesion on posterior scapular spine, that is now enlarging and is starting to become uncomfortable
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Twenty-nine-year-old female with a similar lesion of her proximal femur, that has fractured after sustaining a mechanical fall
Discussion
The correct answer is (C). Osteochondromas are benign lesions that should not grow or begin to become painful after skeletal maturity. If they do, one must be concerned for malignant transformation into an osteosarcoma and further workup is required: an MRI should first be ordered to evaluate the thickness of the cartilage cap, which if greater than 1.5 cm is concerning for, but not diagnostic of, malignancy. The patients described in choices A and B are demonstrating common presentations of osteochondromas about the knee: snapping of muscles or tendons over the lesion, as well as peroneal nerve irritation. The patient in choice D has sustained a fracture of her osteochondroma, which can occur with trauma, but is not concerning for malignancy.
Objectives: Did you learn...?
To recognize osteochondromas on imaging?
When to be concerned about an osteochondroma clinically?
The relevant genetics of osteochondroma and related syndromes?
