Page 662 - Atlas of Small Animal CT and MRI

6.3

Inflammatory disorders

Inflammatory disorders of bone In people, scintigraphy and MRI are considered
sensitive imaging tests for early detection of osteomyelitis.
Osteomyelitis CT and survey radiography are less useful, as results with
Osteomyelitis is most often bacterial, with Staphylococcus these modalities are negative until bone destruction
the most common causative agent. Infection can also be or reactivity occurs. CT features of osteomyelitis are simi-
due to other aerobic and anaerobic bacteria, and mixed lar to those described for conventional radiography
infections are common. Bacterial osteomyelitis most (Figure 6.3.1; see also Figure 4.1.5). When present, a
frequently arises from penetrating injury or surgical sequestrum will appear hyperattenuating to adjacent via-
contamination. Hematogenously disseminated bacterial ble bone and will tend to have sharply delineated margins
osteomyelitis can occasionally occur as a consequence of (Figure 6.3.2). Intravenous contrast administration can
septicemia, and immature and immunocompromised be useful to better characterize soft‐tissue involvement.
animals are more susceptible. Polyostotic osteomyelitis MR features as described in people include marrow T1
is more likely in these patients. hypointensity, T2 and STIR hyperintensity, and enhance-
In certain geographic regions, systemic mycotic infec- ment following intravenous contrast administration (see
tion (Coccidiodes, Blastomyces, Aspergillus, Histoplasma, Figure 3.3.5). Periosteal elevation with T2 hyperintense
and Cryptococcus sp.) can also lead to hematogenously exudates can also be seen in acute infections. Cortical
disseminated osteomyelitis. Protozoal agents, such as bone reactivity and cellulitis may also be detected, depend-
Leishmania sp., can also cause systemic disease with ing on the stage of the disease. 1–7
osteomyelitis as a component.
Although the imaging appearance and progression of Inflammatory disorders of joints
bacterial and fungal osteomyelitis differ, both typically
include mixed destructive and productive bone lesions. Arthritis is often designated as erosive or nonerosive
Acute bacterial osteomyelitis is often accompanied by and either infectious (septic) or immune‐mediated.
regional cellulitis, and the initial destructive and periosteal Immune‐mediated arthritides can be either erosive or
productive responses are ill defined. Chronic bacterial nonerosive, while infectious arthritides are typically
osteomyelitis may appear more contained. A dense, erosive. Because immune‐mediated inflammatory joint
sharply margined sequestrum, surrounding involucrum, disease is a systemic disorder, it generally manifests as
peripheral bone sclerosis, and a cloaca leading to a drain- polyarthritis. 6,8–11
ing open wound are classic features of chronic bacterial
osteomyelitis but are not always present or easily detected. Immune‐mediated arthritis
Fungal osteomyelitis often includes a poorly organized Reports differ on the general signalment of dogs with
productive response that can sometimes mask significant immune‐mediated arthritis. Some suggest that smaller
underlying bone destruction. breeds and females are overrepresented, while others

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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