Presentation
Presents with left axillary mass that has enlarged over the last few weeks.
Patient Data
There is lysis and expansion of the left fourth rib with an associated axillary soft tissue mass. There is also broad-based soft tissue opacity on the pleural surface adjacent to the rib, representing an extrapleural sign. The pulmonary parenchyma and cardiovascular structures are normal.
Aggressive rib mass may be an osteosarcoma or chondrosarcoma.
Case Discussion
A referring veterinarian biopsied the mass, and on histopathology it was a poorly differentiated chondrosarcoma. Differential diagnoses for rib masses include osteosarcoma, chondrosarcoma, hemangiosarcoma, and fibrosarcoma, with osteosarcoma and chondrosarcoma being the most common.
Rib masses may be difficult to identify depending on how they project on the ventrodorsal or dorsoventral projection. A collimated view with different angulation may help to isolate the mass on the images. The mass is indistinct on the lateral projections as it is superimposed on the heart, and shows as a widening of the rib.
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