Page 672 - Atlas of Small Animal CT and MRI

6.4

Neoplasia

Imaging features of axial musculoskeletal neoplasms within the axial skeleton. Primary bone tumors are
are provided in Chapters 1.4 and 3.4. CT and MR imag­ locally aggressive, tend not to cross joints, and metasta­
ing characteristics of appendicular musculoskeletal neo­ size hematogenously to lungs, bone, visceral organs,
plasms are addressed in this chapter. and other tissues. 2–6
Imaging characterization of distal limb osteosarcoma
Primary bone tumors and other bone neoplasms is important when limb
salvage or palliation with radiation therapy or other
Benign bone tumors regional therapeutic techniques is contemplated.
Benign neoplasms of the appendicular skeleton are Accurate assessment of tumor distribution is also neces­
uncommon but broadly include tumors of osteocytic, sary for operative planning of proximal limb neoplasms.
chondrocytic, mixed osteocytic/chondrocytic, and CT features of osteosarcoma and other primary bone
fibrocytic lineage. Although bone architecture can be tumors are similar to those of survey radiography and
significantly altered in these tumors, they tend be more include medullary and cortical bone destruction and
localized with shorter zones of transition and do not periosteal reactive bone production. Tumors that have
have features of active osteolysis or aggressive produc­ osteoblastic features may also produce amorphous,
tive reactivity (see Figure 1.4.10). 1 tumor‐derived new bone. CT may also more clearly delin­
eate internal and extracortical tumor margins compared
Malignant bone tumors to radiographs (Figures 6.4.1, 6.4.2, 6.4.3, 6.4.4).
Malignant bone tumors include osteosarcoma, chon­ Intramedullary tumor invasion replaces normal fat‐rich
drosarcoma, and fibrosarcoma. In some classification marrow, resulting in increased attenuation (Figure 6.4.3).
schemes, other tumors, such as hemangiosarcoma and MR characteristics parallel CT features, with evidence
liposarcoma, are also considered primary bone of defects and remodeling of low‐signal cortical bone.
neoplasms if they arise from within bone. Osteosarcoma Mixed T1 and T2 or STIR intensity tumor soft‐tissue
accounts for at least 85% of all canine bone tumors, and replaces the normally uniformly T1 and T2 hyperin­
about 75% of those involve the appendicular skeleton. tense, STIR hypointense medullary fat and can extend
Older large‐ and giant‐breed dogs are most commonly beyond the external cortical margins (Figure 6.4.5). 6–10
affected, with males overrepresented, and the distal Marked enhancement occurs with both CT and MR
radius, proximal humerus, distal femur, and proximal following intravenous contrast administration. Contrast
distal tibia are the most common anatomic sites. uptake is typically heterogeneous because of regional
Chondrosarcomas comprise the majority of the remain­ hypovascularity or necrosis within the tumor volume.
der of primary malignant appendicular bone tumors, Multiple comparisons of radiography, scintigraphy
although they also have a propensity to arise from CT, and MR have been made to determine which

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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