Cat, british shorthair, Male intact. Almost 3 years of age. Referred from private practitioner for further investigation of a hard space occupying lesion in the left shoulder and lameness on the same limb III/V, progressive for the last 8 months. Radiographs of the region were taken. Radiographic examination Mediolateral and caudocranial view of the left shoulder Radiographic findings There is a severe, extensive, solid, well but irregularly defined periarticular new bone proliferation in the medial aspect of distal scapula and medial part of the proximal humerus (arrows). The humeral head and the distal scapula are deformed and widened. The radio-opacity of the new bone proliferation is only minimally heterogenous, the border are smooth and rounded suggesting a chronic, slow growing process. The most medial part of the joint is affected (arrowhead) and there is surrounding mild soft tissue swelling . Radiographic diagnosis Severe periarticular new bone proliferation centred on the medial part of the left shoulder joint. Differential diagnosis are benign neoplastic process as synovial osteochondromatosis. Other benign processes are less likely.
- The cat underwent biopsy and physiotherapy.
- The lameness improved but was still present (I-II/V) 3 months after the presentation.
- Radiographic re-check was performed 3 months later.
- The histologic diagnosis of the sampled area was enchodral ossification.
Mediolateral (left) and caudocranial (right) view of the left shoulder 3 months later. Comments
- Synovial osteochondromatosis are described as island of cartilage produced by the synovial membrane. Foci of cartilage become pedunculated and may become separated from their pedicles to form loose bodies within the joint.
- Burmese cats are overrepresented.
- The radiographic appearance is very variable. Usually the lesions are well-defined, rounded, often there are multiple intraarticular nodules of mineral opacity. Not all the chondromas become calcified; contrast arthrography may be necessary for the diagnosis.
- Synovial osteochondromas may arise also from extraarticular foci of synovial tissue.
- The cause is unknown, but the theory of synovial metaplasia is generally accepted.
- Other conditions in cats in which intraarticular and periarticular mineralization may be confused with synovial osteochondromatosis are mild form of mucopolysaccaridosis VI and hypervitaminosis A.
