• Inflammatory arthropathy with erosive/cystic bony change
  • Infectious arthropathy
  • Gout
  • Pigmented villo-nodular synovitis (PVNS)
  • Intra-osseous ganglion
  • Degenerative cysts


  • Osteoid osteoma
  • Synovial chondrometaplasia
  • Chondroblastoma


  • Inflammatory conditions are suspected by a history of multiple joint involvement and loss of joint space.
  • Calcified tophi may be observed in gout
  • PVNS has a typical history of atraumatic effusions at the knee and diffuse soft tissue swelling at the foot and ankle. MRI is particularly useful in diagnosing PVNS because hemosiderin deposition results in regions of low intensity on both T1 and T2 weighted images. Intra-osseous ganglion or degenerative cysts can also be diagnoses on MRI.
  • Synovial chondrometaplasia is easily diagnosed on plain radiographs when lesions are partially calcified. In instances of non-calcified lesions, MRI may be helpful in characterizing the synovial changes and detecting intra-articular loose bodies.
  • Peri-articular osteoid osteoma may cause joint effusion and inflammatory symptoms. The nidus of osteoid osteoma may be difficult to locate in a peri-articular location, however.
  • Chondroblastoma is included in this list because its epiphyseal location may be mistaken for a joint cyst.

Other Differential Diagnoses by Anatomic Location