Clinical history A 35 kg 4year 8month old female Bernhardiner presented with acute swelling on the distal antebrachium medially and cranially - the lesion was warm and painful on palpation. Radiographs were made of the affected limb. Views of the distal antebrachium Enlarged views Radiographic changes - radius Central destructive lesion distal metaphysis Overlying cortical thinning Periosteal reactive new bone surrounding the lesion that fails to have an intact border periosteal new bone between the radius and ulna Long zone of transition between the lesion and normal appearing bone Failure of the lesion to spread across the joint space Minimal soft tissue swelling medial and cranial Radiographic changes - ulna Radial lesion appears to invade the adjacent ulna. - Small destructive foci within the ulnar medullary cavity - Ulnar cortical destruction adjacent to the radial lesion - Small foci of increased density attached to the endosteal surface proximally in the ulna (arrow) - Suggestion that the periosteal new bone between the radius and ulna is associated with an expansile lesion originating from the radius Radiographic diagnosis A destructive lesion of this appearance in the distal radial metaphysis of a large breed dog is most likely a primary bone tumor and most likely an osteosarcoma (80-85% of primary bone tumors are osteosarcomas). An osteomyelitis would have a better defined border to the lesion, a shorter zone of transition, and a more intact border to the periosteal new bone. Comments Radiographs of the thorax failed to identify pulmonary metastasis. Typically, primary bone tumors do not extend into adjacent bones - finding destructive changes in the ulna in this dog is unusual and may suggest an increased malignant tendency of the tumor - a rule that primary bone tumors are monostotic remains useful in radiographic diagnosis and perhaps needs only to be changed to a rule that states that the primary bony change is found in a single bone with any change seen in an adjacent bone being of lesser magnitude suggesting a later developing pattern.
