9-Year-Old MN Saint Bernard

Signalment & History

A 9 year old MN Saint Bernard presents for severe lameness and soft tissue swelling proximal to the stifle.

CC left stifle Lateral left stifle


Aggressive osteolytic lesion involving the distal left femoral metaphysis. The cranial and lateral cortices have been destroyed. A motheaten
appearance is noted surrounding this large lytic area. This area measures 44 x 22 mm. Soft tissue mass is noted extending from this region and a cranial and lateral direction. An ill-defined periosteal reaction and/or amorphous osseous proliferation is noted. Irregular periosteal reaction is noted along the caudal cortex at the level of this lytic lesion. Entheseophyte formation and mild periarticular osteophyte formation is noted associated with the patella.


Aggressive, monostotic, metaphyseal distal femoral osseous lesion compatible a primary bone tumor


In this case, we can find features of aggressive osseous disease, such as cortical disruption, ill-defined zone of transition, and motheaten osseous lysis. There is not a lot of periosteal proliferation in this case. The two main differentials for this aggressive radiographic appearance are neoplasia and infection. Considering the location of the lesion (distal femoral metaphysis) and age of the patient, primary osseous neoplasia is more likely. Osteosarcoma was confirmed via histology. Other common sites to develop primary bone neoplasia in dogs are the metaphyseal region of the following bones: proximal humerus, distal radius, and proximal and distal tibia.