11-year-old castrated male Jack Russell Terrier

There were 2 major observations in this case:

• Destructive lesion of the proximal left 3rd rib
• Normal left shoulder

• Based on the presence of rib destruction the candidate was expected to identify an aggressive lesion of the rib (extrapleural mass) with primary differentials of osteosarcoma and chondrosarcoma.
• The candidate was also expected to indicate that the left shoulder was normal.

• Thoracic radiographs – to further evaluate the rib lesion and to evaluate for metastatic disease.
• Computed tomographic study – to evaluate the size of the rib lesion +/- to evaluate for metastatic disease.
• Biopsy of the mass.

In general the candidates did well on this case. The unsuccessful candidates failed to identify the rib lesion . These candidates then described lytic changes associated with the left shoulder (usually the proximal humerus and occasionally both the humerus and scapula). Some candidates described an osseous fragment at the medial margin of the shoulder, failing to recognize a normal clavicular remnant.

The unsuccessful candidates demonstrated a weakness that was noted throughout the musculoskeletal section – lack of knowledge of normal anatomy and inability to identify variation in appearance of normal structures due to positioning and technique.