Presentation
Presents with previous palliative radiation therapy for osteosarcoma and increasing lameness.
Patient Data
Left pelvic limb: There is profuse, irregular new bone formation and destruction of the distal tibia and fibula. There is new bone production cranial to the tarsus as well as caudal to the tarsus. There is a short, oblique, radiolucent line traversing the distal metaphysis and epiphysis of the tibia. Smooth periosteal reaction extends to the mid-diaphysis of the tibia with medullary sclerosis.
Throax: The cardiovascular structures are normal in size and shape. There is a small, opaque nodule superimposed over the second ribs on the left lateral projection and the right lateral projection. An ill-defined nodule is superimposed over the diaphragm on the right lateral projection. The remainder of the pulmonary parenchyma appears normal. There is increased soft tissue opacity dorsal to the second sternebra.
Pathologic fracture of the distal tibial osteosarcoma
The dense appearance of the tumor is likely secondary to radiation therapy
Pulmonary metastatic disease
Sternal lymphadenopathy may be reactive or metastatic.
There is a mineralized nodule in the left cranial lung lobe adjacent to the medistinum. In the ventral mediastinum, an enlarged lymph node is visible.
Metastatic osteosarcoma in the lungs and mediastinal lymph node are likely. Alternatively, heterotopic bone and reactive lymph nodes are differential diagnoses.
Case Discussion
Osteosarcoma causes aggressive bone lesions in typical sites including the distal tibia. The new bone produced by the tumor is smoothed after being treated with radiation therapy. However, the weakened bone has fractured causing increased lameness. Metastases of osteosarcoma are not often mineralized. Differentials for a mineral opacity nodule include osteosarcoma and heterotopic bone, a degenerative change in older dogs. In a young dog with osteosarcoma, neoplasia is prioritized. No further diagnostics were performed on the thorax. Osteosarcoma was confirmed by histopathology.
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