Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Four The Appendicular Skeleton 517
Fig. 4-54 A 9-year-old mixed breed dog with a right hind limb lameness
of 2 months duration that had become more severe in the last
week. Soft-tissue swelling was present. Examination of the anteroposterior
view of the distal right femur reveals a lytic, expansile lesion of
the distal femur. There is a pathologic fracture present (arrow).
Diagnosis: Giant cell tumor.
well-defined lytic foci. 120,178,179 Minimal amounts of periosteal proliferation may be present.
180,181 Soft-tissue mineralization has been observed occasionally. The tumor has a tendency
to remain confined to the medullary cavity while expanding proximally and distally.
Pathologic fractures may occur.
Myeloma. Plasma cell myeloma occurs occasionally as a solitary lesion but more commonly
as multiple lesions. 182-188 The lesions may involve any long or flat bones. The bony
changes usually are well-defined, discrete areas of cortical lysis that lack sclerotic margins
(Fig. 4-53). Occasionally, these may show some proliferative change. 183,185 Rarely, a generalized
loss of bone density may be all that is observed (see Fig. 6-42).
Liposarcoma. A few liposarcomas of bone have been reported. 135 Multiple areas of metaphyseal
bony lysis and reactive periosteal proliferation were described.
Giant Cell Tumor. The giant cell tumor is an unusual tumor of bone. 189-193 It is characterized
by a lytic, expansile lesion of the metaphysis and epiphysis (Fig. 4-54). The appearance
can be very similar to a bone cyst, but the zone of transition usually is longer and less
distinct with giant cell tumor.
Lymphoma of Bone. Primary lymphoma of bone is an unusual manifestation of
lymphoma. 130,194-202 It is characterized radiographically by multiple focal to confluent
areas of osteolysis, which do not have sclerotic margins (Fig. 4-55). Multiple bones usually
are involved. Periosteal reaction is rare except in cases with concomitant pathologic
fractures.