Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Four The Appendicular Skeleton 513
A
B
Fig. 4-48 A and B, A 9-year-old male Golden Retriever with a right rear limb lameness. There was
pain on manipulation of the stifle and a palpable mass. There is a bony mass on the medial aspect of
the proximal tibia. The margins of the mass are well defined with a thick cortical shadow. The bony
lesion appears to be contiguous with the medullary canal. Diagnosis: Parosteal osteosarcoma.
Chondrosarcoma. Although chondrosarcomas may affect long bones, they most
frequently arise from flat bones such as the pelvic bones, scapulae, or ribs (Figs. 4-49 and
4-50). 130,162-164 This tumor occurs more often in older, medium-breed, and large-breed
dogs and rarely affects giant-breed dogs or cats. 165 Chondrosarcomas usually are highly
destructive masses. Mineralizations in the soft-tissue mass frequently appear as multilobulated
globules called popcorn mineralization, but they may also appear less organized.
Chondrosarcoma may arise at the site of an osteochondroma or cartilaginous
exostosis. 166
Fibrosarcoma. Fibrosarcoma has been reported in young and old dogs and cats. 130,167-172
It typically produces an osteolytic lesion in the metaphysis of the long bones (Fig. 4-51). A
large soft-tissue mass without mineralization may be present. Periosteal new bone formation
is rare.
Malignant Fibrous Histiocytoma. Malignant fibrous histiocytoma is thought to be a
tumor of histiocytic origin. Radiographically the lesion is similar to that seen with fibrosarcoma.
Bony changes are predominately lytic. Minimal periosteal reaction may be present.
The lesions tend to be poorly defined and may have associated soft-tissue swelling. 173-177
Hemangiosarcoma. Hemangiosarcoma is a highly destructive lesion that usually involves
the metaphysis or diaphysis of a long bone (Fig. 4-52). The pattern of destruction typically
manifests as an overall osteopenia with a superimposed pattern of numerous, small,
Text continued on p. 517