Primary synovial osteochondromatosis has a variety of radiological appearances ranging from the pathognomonic plain film appearances to the more unusual non-mineralised extraarticular manifestation of the disease. The less common manifestations of the disease require multimodality imaging to make the diagnosis. CT and MRI are particularly useful in fully characterising primary synovial osteochondromatosis and to allow for appropriate surgical planning to minimise disease recurrence.

As a tertiary centre for soft-tissue sarcomas, numerous non-neoplastic masses are referred to our institution. In many cases, review of the imaging allows a confident diagnosis to be made without the need for biopsy. Lesions include anomalous muscles and variants, muscle injury, haematoma, myositis ossificans, aneurysm, abscess, tumoral calcinosis, amyloidosis and elastofibroma. The purpose of this article is to review the imaging characteristics of these non-neoplastic lesions and highlight the features that help differentiate these lesions from a soft-tissue sarcoma.

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