2013 Radiology Exam - Musculoskeletal Case 1

Signalment:  11 year old neutered male mixed breed.

History:  Right carpal mass and soft tissue swelling with mild lameness in the right fore limb.

Radiographs: Four images of the right carpus; dorsopalmar, flexed lateral, dorsomedial-palmarolateral and dorsolateral-palmaromedial.

Observations:

  • Soft tissue swelling is present around the carpus with a focal increase in soft tissue opacity on the medial and caudal aspect of the carpus.
  • A focal area of osseous lysis is present in the caudal and medial aspect of the distal radius.
  • Additional focal areas of osseous lysis are present in the accessory, radial, first, second and fourth carpal bones.
  • There is mild widening of the accessory/ulnar carpal joint space.
  • The subchondral bone in all carpal joints is intact and there is no osseous production or areas of osseous sclerosis.

Synthesis:

  • Based on focal soft tissue swelling, multiple areas of osseous lysis in the distal radius and carpal bones with no osseous production or sclerosis and intact subchondral bone, a soft tissue neoplastic mass invading into the adjacent bones with primary differentials of synovial cell sarcoma, histiocytic synovial sarcoma or myxomatous sarcoma.

Case Management:

  • Biopsy of the soft tissue mass.
  • Joint centesis to obtain fluid for analysis could be considered.
  • Three view thoracic radiographic examination to check for metastatic neoplasia.

In general candidates did well on this case. Some candidates only saw the lesion in the distal radius and did not identify the more subtle lesions in the adjacent carpal bones. Diagnoses such as a bone cyst in the radius, septic arthritis and immune mediated arthritis were provided which were OK to include in a differential diagnosis if soft tissue neoplasia was the primary diagnosis and the reasons for the order of the differential diagnosis based on the radiographic findings were given.

Unsuccessful candidates failed to recognize the osseous lytic changes or associate the lytic changes with the absence of bone production and intact subchondral bone to provide an appropriate differential diagnosis.