Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

480 Small Animal Radiolo g y and Ultrasono graphy
Fig. 4-2 A 6-year-old spayed Great Dane with a chronic soft-tissue
infection of the right front foot. There is extensive bony proliferation
involving the cranial medial aspect of the distal radius; radial carpal
bone; first, second, and third metacarpal bones; and first and second
phalanges of the second digit. The bony proliferation is smooth and
well mineralized, and possesses an organized trabecular pattern.
Diagnosis: Benign or chronic inflammation. In this case, the reaction
is secondary to chronic soft-tissue infection.
Radiographs must be evaluated systematically. One approach involves sequentially
examining the soft tissues surrounding the bone, the periosteal and endosteal surfaces,
the cortical thickness and density, the medullary density and trabecular pattern, the
articular surfaces, the subchondral bone density and thickness, and the joint space
width.
Interpretation of a bone lesion requires knowledge of the age, breed, and species
involved, the usual site or sites of involvement (i.e., specific joint, bone, or location within
the bone), the number of bones or joints involved (i.e., monostotic or polyostotic, monoarticular
or polyarticular), and whether a disease usually is localized or generalized. 31,32
Bone can respond to stress or injury only by removal of existing bone via destruction or
osteolysis, or by adding new bone via bony proliferation or sclerosis. A loss of 30% to 50% of
the bone density is required before the loss can be detected radiographically. When bony
destruction is present, (1) alteration of the trabecular pattern or loss of the normal bone density
within the medullary canal or subchondral bone or (2) a decrease in cortical thickness or
break in cortical continuity may be seen. Bone loss within the cortex may be detected more
easily than bone loss within the medullary canal. Bony proliferation may originate from the
periosteum (outer cortical margins) or endosteum (inner cortical margin) or within the
medullary canal.
The aggressiveness, activity, or rate of change of a bony lesion can be estimated by evaluating
the amount and nature of the bony destruction and proliferation that is present and the
margin between the normal and abnormal bone. Slowly progressive, inactive, nonaggressive, or
benign bone or joint lesions are characterized by well-mineralized, uniformly dense, smooth
margins on periosteal and endosteal surfaces; well-defined lines of transition; and an organized
trabecular pattern in the medullary canal (Fig. 4-2). Rapidly progressive, active, aggressive, or
malignant bone lesions have poorly defined, irregular, unevenly mineralized margins and a
gradual, ill-defined transition between the normal, uninvolved bone and the lesion (Fig. 4-3).
Special radiographic procedures have been described for evaluating both bones and joints.
Contrast arthrography (i.e., positive, negative, or double-contrast techniques) has been used