Chondrosarcoma arising from exostosis

Case contributed by Dr Dinesh Brand

Presentation

Bone pain with prior history of fracture and exostosis.

Patient Data

Age: 20
Gender: Male

There is a circumscribed enchondral lesion with a central matrix including cartilaginous and "popcorn" calcification; expansion is limited to less than the maximum width of the nearest metaphysis; these features are typical of an osteochondroma (enchondroma).

There is a further expansile pedunculated bony lesion of the cortex demonstrated in relation to the mid shaft of the femur in keeping with an exostosis.

There is a lobulated calcified mass on the medial aspect of the distal shaft of the left femur. The lesion has a pedicle and appearances are keeping with an exostosis. There is associated low attenuation area containing foci of calcification surrounding the mass. The soft tissue mass lesion is noted within the vastus intermedius muscle and is displacing the adjacent vastus medialis. There is an impression of involvement of the endosteum at the level of the pedicle. 

The distal shaft femoral mass lesion with aggressive features has appearances most likely representing a juxta-cortical/periosteal chondrosarcoma associated with a previous bony exostosis.

There is a sessile osteochondroma in the left femur metaphyseal region medially and typically projecting away from the epiphysis. There is a low to intermediate T1W signal mass around the exostosis. The mass lesion is iso- to slightly hyperintense compared to muscle. The cartilage cap is thick with rings and arcs calcification and there is irregular subchondral bone. The lesion is noted within the vastus intermedius muscle. The mass is distant to the femoral neurovascular bundles.

The appearances are in keeping with an osteochondroma (exostosis) of the femur. The presence of aggressive features such as bony destruction, large soft tissue component are suggestive of malignant transformation. 

Case Discussion

Chondrosarcomas are usually located outside the medullary canal of the bony component. When an osteosarcoma is diagnosed, it is usually a dedifferentiation of a preexisting peripheral chondrosarcoma​1

This patient had a previous history of femoral fractures and exostosis. He developed new symptomatic bony pain, raising the possibility of osteosarcoma once seen on x-ray findings. Changes in the marrow of the exostosis and medullary canal of the bone on CT and MR imaging was seen. Associated destruction of the cortex and soft-tissue involvement gave a differential diagnosis of chondrosarcoma 1.

A study found that cases of degeneration of osteochondromas to chondrosarcomas occurred in patients with previous or existing multiple exostoses, and their average age was 34.9 year 2.

Specialist oncology review is needed in this case to determine management and treatment plan.

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Case information

rID: 59996
Published: 10th May 2018
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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