Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Four The Appendicular Skeleton 521
minimal unless cortical penetration has occurred. Soft-tissue mineralization and marked
periosteal responses are rare. The margins of the lesion usually are poorly defined. If a
metastatic tumor is suspected, the patient should be evaluated for a primary soft-tissue
neoplasm, which often is carcinoma of the lung, mammary gland, or prostate. Bony metastasis
may be present with or without pulmonary metastasis.
A particular syndrome in cats of metastasis of lung tumors to multiple toes, especially
in the front feet, has been described. It is associated with soft-tissue swelling, bony lysis, and
minimal periosteal response (Fig. 4-59). 214-217
S O F T-TISSUE T U M O R S
Soft-tissue tumors arise from the soft tissues adjacent to bones and joints and affect them
by direct extension. These tumors may involve adjacent bones. The pattern of destruction
usually is centered on one aspect of the cortex (Fig. 4-60).
Synovial Cell Sarcoma. Synovial sarcoma frequently involves more than one bone in a
joint. Although any joint may be involved, it is observed most often in the elbow and stifle
(Fig. 4-61).
This tumor usually crosses the joint space to involve the adjacent epiphyseal and metaphyseal
areas. The lesion is predominantly osteolytic, periosteal proliferation is minimal,
and soft-tissue mineralization is rare. 218-223 A differential consideration with these lesions
must be excessive synovial hypertrophy or hyperplasia secondary to chronic joint conditions.
A
B
Fig. 4-61 A and B, A 7-year-old male Standard Poodle with a 1-month history of a mass on the left
carpus. The size of the mass appeared to increase rapidly. There is marked local soft-tissue swelling
centered over the carpal-metacarpal joint. There is marked bony destruction involving the distal ulna,
distal radius, accessory carpal bone, radial carpal bone, and metacarpal bones. A small amount of
bony proliferation is seen caudal to the ulna (arrow). There is a small amount of soft-tissue mineralization
on the caudal aspect of the carpus (arrowhead). Diagnosis: Soft-tissue neoplasm invading the
carpal joint. This neoplasm was identified as a synovial cell sarcoma.