What is the differential diagnosis?
The features are most likely those of a soft tissue sarcoma. Synovial sarcoma and malignant fibrous histiocytoma (MFH) are the most likely diagnoses (the former is usually within 5 cm of the joint, the latter usually in older patients). Other sarcomas could appear indistinguishable (e.g. fibrosarcoma).
This tumour was shown to be a synovial sarcoma. How frequently do these tumours demonstrate calcifications?
Approximately 30%.
What are some poor prognostic factors for synovial sarcomas?
There are many: large size (> 5cm) : most important factor; located in the trunk or head and neck; older patients; cystic / haemorrhagic components; marked heterogeneity; certain histologic features (refer to related article).
Bone scan demonstrates elevation of activity on both dynamic and blood pool views. Bone phase shows only minor local increase (not shown).