This is an x-ray of a known patient with pigmented villonodular synovitis, MRI was missed. PVNS is essentially an MRI diagnosis, but this is an example of plain radiograph features. Its appearance on a radiograph is not diagnostic and has many differentials.

Editor's note: Per the 2020 WHO Soft Tissue and Bone Tumors Classification (5th ed.), the recommended terminology is tenosynovial giant cell tumor with pigmented villonodular synovitis no longer recommended (although remains in common use).