11-years-old male crossbreed was presented with a mass at the right elbow. A CT-scan of the elbows and thorax was performed A thoracolumbar spine and thoracic CT scan was performed.
There is a mixed lesion, mostly osteoproliferative, with aggressive characteristics affecting the distal third of the diaphysis and metaphysis of the right humerus (pink circles). This lesion shows a permeative/moth-eaten lysis, as well as a marked periosteal reaction with a solid component in the proximal region and an amorphous component in the distal region. The lesion also has a soft tissue component surrounding the periphery of the osseous changes, showing heterogeneous enhancement. It does not appear to affect the elbow joint, although there is a mild periosteal reaction/irregular new bone formation at the proximal aspect of the anconeal process (orange arrows) and at the cranioproximal aspect of the radius. There are no abnormalities at the left elbow.
There is a small, round and ill-defined peribronchial soft tissue lesion in the cranial aspect of the left caudal lung lobe (pink arrows).
The right axillary lymph node is mildly enlarged (pink arrows).
- Aggressive monostotic lesion affecting the distal diaphysis/metaphysis of the right humerus, most likely consistent with primary bone neoplasia (e.g. osteosarcoma). Non-neoplastic processes (e.g. fungal osteomyelitis) are considered very unlikely. The mild changes at the level of the anconeal process and radius could represent degenerative changes due to the mass effect of the lesion on the periarticular soft tissue; periosteal reaction of neoplastic origin is considered less likely.
- Nodular lesion in left caudal lung lobe most likely consistent with solitary pulmonary metastasis.
- Mild right axillary lymphadenopathy consistent with incipient metastasis vs reactive.
The findings are consistent with an aggressive humeral bone lesion suggestive of a primary bone tumour, associated with mild right axillary regional lymphadenopathy and a solitary pulmonary nodule, which may indicate incipient metastasis. The definitive diagnosis of the lesion in the right humerus requires histopathological analysis. In addition, FNA of the lymph node and monitoring of the lung lesion is recommended in order to confirm metastatic origin.