What’s the Diagnosis – Case 171
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Findings Comparing the radiographs dating back to 2013, there are very subtle areas of mineralization about the inferior medial aspect of the acetabulum (not able to be appreciated prospectively and extremely difficult even retrospectively). The MRI demonstrates a destructive, T2 hyperintense, lobulated mass that extends across the joint and involves the lesser trochanter. Enlarged pelvic sidewall lymphadenopathy is also present.
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Diagnosis: Chondrosarcoma In this case, the radiographs are an extreme example of an “eye test”. Even in retrospect again, the findings are nearly impossible to perceive, but there is a faint mineralization in a ring and arc pattern as seen in cartilage lesions. The T2 hyperintense and lobulated architecture is often found in cartilage lesions although as in this case, there is often a prominent degree of heterogeneity. The very aggressive nature of this lesion accounts for not only the spread into the joint but also the extension to the lesser trochanter. Chondrosarcoma is a lesion of adult and older patients, often with an insidious onset and having a slight male predominance. The lesion can affect many locations including metaphysis/diaphysis of long bones, innominate bone, ribs, vertebrae, and craniofacial region. As stated in the literature, in this case, and in our experience, the lesions of the pelvis tend to be centered around the prior tri-radiate cartilage, be very destructive, and lead to a complete destruction of the joint. Metastases are most frequent of the lungs, liver, and regional lymph nodes (shown in this case). The differential in this case would certainly include metastasis and lesions/pathology related to the arthroplasty itself. Metastasis do not tend to produce such a large soft tissue component or extend into joints but are so much more common that they always have to be considered. Processes related to the arthroplasty itself are a bit trickier.
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Diagnosis: Chondrosarcoma Processes such as prosthetic joint infection, polymeric wear induced synovitis, and adverse local tissue reaction/metallosis could mimic what is shown in this case. However, those processes are more joint centered with extension into the bone then bone centered as seen here. Also, those processes tend to produce a much greater degree of often bulky synovitis which is not found in the setting of malignancy. This is one time where experience is very helpful in trying to arrive at the appropriate differential diagnosis. On the following slides, please see the typical architecture of a joint centered, bulky synovitis of polymeric wear induced disease as an example.
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References Imaging of Primary Chondrosarcoma: Radiologic-Pathologic Correlation1. Mark D. Murphey, Eric A. Walker, Anthony J. Wilson, Mark J. Kransdorf, H. Thomas Temple, Francis H. Gannon. RadioGraphics Vol. 23, No. 5, Sep 1 2003, https://doi.org/10.1148/rg.235035134
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