Page 1391 - Clinical Small Animal Internal Medicine

150 Tumors of Bone and Joint 1329

(a) (b) While micrometastatic disease is thought to be pre-
VetBooks.ir sent in nearly all dogs diagnosed with appendicular OSA,
gross metastasis is only identified in about 10% of cases
at the time of initial diagnosis. Pulmonary and bony
metastases occur with approximately equal frequency at
the time of initial diagnosis, although metastasis to other
locations is possible.
Staging of patients is performed due to its relevance in
estimating survival time. Little distinction is made in
osteosarcoma regarding histologic grade due to the bio-
logic aggressiveness of these tumors in nearly all cases;
however, the presence of gross metastasis (stage III dis-
ease) is associated with shorter survival times. Median
survival times (MST) in dogs with stage III appendicular
OSA are still highly variable, however, and are affected
by treatment provided. Grading of non‐OSA sarcomas is
generally thought to be associated with prognosis, with
grade III tumors much more likely to metastasize and
associated with a shorter survival time.
Staging in all cases should include three‐view thoracic
radiographs to evaluate for pulmonary metastasis.
Abdominal ultrasound may also be performed to check
for metastatic disease, particularly in cases with pelvic
limb neoplasia, lymphadenopathy, atypical presentation/
clinical findings, or in patients with histiocytic disease.
Similarly, lymph node aspirates should be performed
when lymphadenopathy is noted on physical examina-
tion or imaging studies or if the regional lymph node is
readily accessible.
Figure 150.1 Orthogonal view radiographs (cranial‐caudal (a), Nuclear scintigraphy, performed with an intravenous
lateral (b)) of the right radius and ulna. An expansile and lytic injection of technetium‐99m, allows for identification of
lesion of the distal radial metaphysis is identified with associated skeletal abnormalities with increased metabolic, particu-
soft tissue swelling. Cytologic aspirate of this lesion was consistent
with osteosarcoma. larly osteoblastic, activity. This diagnostic tool is highly
sensitive but lacks specificity; areas of increased uptake
may be due to neoplastic disease, infection, fracture, or
neoplasia, although differentiation between types of can- other orthopedic co‐morbidities. The input of an experi-
cer is often not possible with cytology alone. ALP staining enced radiologist, as well as follow‐up radiographs to
of cytologic samples may allow for more conclusive iden- evaluate abnormal areas, can help to distinguish between
tification of OSA in some cases. When indicated or these differentials.
desired, bone biopsy can be performed which typically Computed tomography (CT) is being increasingly
results in a specific tumor diagnosis in about 80% of cases. used, both to evaluate for thoracic metastases and for
Bone biopsy may be performed using an incisional evaluation of the local tumor site. While traditional,
technique, Michele trephine, or Jamshidi needle. high‐quality radiography is able to detect pulmonary
Jamshidi needles yield a smaller biopsy but provide a diag- metastases that are approximately 7–9 mm in size, CT
nosis in the vast majority of cases. Bone biopsies should has a reported sensitivity for detection of lesions as small
be planned in order to minimize the size of the surgical as 1 mm. Despite this improved detection of disease, the
site and provide for appropriate tumor excision at the clinical relevance of smaller metastatic lesions with
time of definitive surgery. Samples should always be taken regard to survival times is uncertain.
from the center of the lesion, as a peripheral biopsy is Assessment of the local tumor site in appendicular
more likely to yield reactive bone rather than the true dis- OSA with CT is generally nonessential when the chosen
ease process. In addition to using the smallest sampling treatment is amputation. CT may help to evaluate the
tool thought likely to provide a diagnostic sample, it is extent of disease if alternative surgical treatments such
also recommended to avoid penetration of both cortices as limb‐sparing surgery are to be considered. In addition,
to minimize the likelihood of pathologic fracture. CT is often highly valuable for surgical planning in cases