Clinical history The dog presented with minimal lameness on the front leg - The owner had only had possession of the dog for several weeks and knew little concerning its earlier medical history. The dog was a 3 year old, male, mixed breed. There was minimal swelling proximal to the carpus without pain evident on palpation. Radiographs made on presentation Radiographs made on presentation Radiographic changes A lytic lesion with cortical disruption was noted in the distal radial metaphysis. Minimal reactive bone was noted around the lesion. The lesion was difficult to identify on the craniocaudal view. Differential diagnosis based on the destructive appearance of the lesion Osteomyelitis probably secondary to a bite wound. Hematogenous osteomyelitis. A fracture with delayed healing. Primary bone tumor. Metastatic bone tumor. The owner was advised that considering the lesion was causing minimal clinical discomfort, it would be possible to wait and reexamine the lesion in 1-2 weeks - • However, because of the destructive nature of the lesion and the concern of the owner, it was decided to biopsy the lesion. In the interim prior to the biopsy, the owner was instructed to attempt to learn more of the earlier medical history of the dog. Fortunately, the previous owner was located and earlier radiographs were forwarded for evaluation. Radiographs made 60 days earlier Radiographic diagnosis The lesion had undergone minimal change in the time interval making the diagnosis that of a benign lesion probably a slowly healing fracture that had not received treatment. The fracture had developed minimal callus at the time of the first radiographs suggesting a chronic injury at that time. Ulnar fractures of this nature often heal with a fibrocartilaginous callus because of the absence of stress at the fracture site that would otherwise stimulate a bony callus formation. Comments Discovery of the original radiographs made the diagnosis of a somewhat confusing case rather simple - the decision to reexamine the lesion in 1-2 weeks is thought to be a satisfactory approach to the case - the absence of progression of the lesion would suggest a benign process - While a biopsy sounds as a definitive technique in reaching a diagnosis, healing fractures often contain a pattern of plump mesenchymal cells surrounded with osteoid and are a feature of fracture repair that may easily be confused with an osteosarcoma - * *Thompson and Pool in Tumors in Domestic Animals, Blackwell Publishing 4th ed 2002.
