SYNOVIUM - Villonodular synovitis

The specimen shows fine fronds of pigmented tissue, sometimes discrete and sometimes matted together forming small nodules of brown tissue. These arise from a pale membrane.
This young woman presented at the age of 19 with a six-month history of swelling and instability in her left knee which had apparently been a sequel to a minor strain. On examination she had quite considerable effusion and synovial thickening in both knees and subsequently the lesion seen here. The left knee which clinically was similarly affected, was later explored but this showed only an effusion and the presence of a large medial synovial plica. This was excised and both knees are now essentially trouble-free. The histology of the lesion is that of villonodular synovitis; the pigmentation is due to the deposition of haemosiderin. The aetiology of the condition is obscure but it is regarded as non-neoplastic.