Page 470 - Atlas of Small Animal CT and MRI

460 Atlas of Small Animal CT and MRI

causes vary, these disorders have characteristic constel- patterns, CT features have not been characterized in com-
lations of CT features that are adequate for specific diag- panion animals because conventional radiography would
nosis, and most eventually lead to end‐stage pulmonary likely be used as an initial imaging diagnostic test. Based
fibrosis. These entities have not been well described in on reported radiographic features of viral pneumonia in
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dogs and cats, but we do occasionally encounter patients dogs and cats, one might expect to see interstitial, ground‐
with histologically confirmed interstitial pneumonitis glass opacities regionally or diffusely distributed, with a
without an apparent underlying infectious or other non- predilection for the caudodorsal lung fields.
infectious exogenous cause (Figure 4.6.9).
Aspiration pneumonia
Eosinophilic bronchopneumopathy Aspiration pneumonia, as the name implies, results from
Canine eosinophilic bronchopneumopathy is thought to aspiration of gastric or other fluids that cause a chemical
be immune‐mediated and the result of a hypersensitivity pneumonitis. Gastric fluid is acidic and is therefore par-
to aeroallergens, although infectious and other immune‐ ticularly damaging. Swallowing and esophageal disor-
mediated causes have also been proposed as initiators in ders and gastric reflux are common predisposing factors
some instances. Average age of onset is 4–6 years, and leading to aspiration. Aspiration pneumonia typically
both large‐ and small‐breed dogs are affected. Females are occurs in the dependent regions of affected lobes but
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at over twice the risk for developing the disease. Although may have an atypical distribution if aspiration occurs
there is not a clear consensus regarding features, our expe- with the patient in lateral or dorsal recumbency, as can
rience suggests three clinical manifestations. Some dogs occur while under anesthesia. Bacterial contamination
present with a predominantly bronchitic manifestation, will lead to lobar pneumonia.
with CT features of bronchial wall thickening and evi-
dence of intraluminal bronchial exudates (Figure 4.6.10). Bacterial bronchopneumonia and related
Other dogs have findings more similar to bronchopneu- disorders
monia with mixed interstitial and alveolar infiltrates. Less In people, bacterial pneumonia is subdivided into
commonly, the disorder manifests as pulmonary granulo- bronchopneumonia and lobar pneumonia, reflecting
mas that appear as focal, multifocal, or regional irregularly the initial location and subsequent progression of
margined nodules or masses (Figure 4.6.11). the inflammatory process. Bronchopneumonia arises
through accumulation of exudates in terminal bronchi-
Lipid pneumonia oles and respects septal boundaries. Lobar pneumonia
Endogenous and exogenous lipid pneumonia has been results from alveolar flooding of inflammatory exudates
reported in both dogs and cats. 14–18 Endogenous lipid and has a greater propensity to spread. Given the differ-
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pneumonia results from pneumocyte injury with a wide ences in subgross anatomy between people and compan-
array of proposed toxic, metabolic, and nutritional ion animals, this distinction may not be relevant in cats
causes. Radiographic features of endogenous lipid pneu- and dogs. CT features of bacterial bronchopneumonia
monia in a report of 24 cats included pleural effusion, include mixed interstitial and alveolar infiltrates in
diffuse interstitial or bronchointerstitial infiltrates, mul- dependent regions of involved lung lobes. In many
tifocal pulmonary infiltrates with confluence near the instances, complete lobar consolidation occurs with air
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hilus, and discrete pulmonary nodules. CT features of bronchograms surrounded by uniformly soft‐tissue
endogenous lipid pneumonia have not been reported in attenuating alveolar infiltrates. Lung volume loss can
dogs or cats (Figure 4.6.12). occur but is usually mild and insufficient to explain the
Exogenous lipid pneumonia is most often linked to increased lung attenuation (Figure 4.6.13). Mycoplasma
aspiration of lipid‐based medications. In people, CT fea- pneumonia has been reported in both cats and dogs and
tures include diffuse ground‐glass interstitial opacities, appears to include airway collapse and bronchitis as part
consolidation, or mass lesions. 19,20 A single case report of the clinical manifestation in addition to consolidating
describing CT findings in a dog with exogenous lipid pneumonia (Figure 4.6.14). 22,23 Pleuropneumonia can
pneumonia characterized the lesions as lung consolida- lead to pleural thickening and regional pleural effusion,
tion with air bronchograms. The affected region mildly and necrotizing bronchopneumonia can result in pneu-
and diffusely contrast enhanced. 14 mothorax (Figure 4.6.15).
Foreign‐body‐induced bronchopneumonia is com-
Viral pneumonia mon in some parts of the world where ingested or inhaled
Although CT appearance of viral pneumonias has been plant awns migrate down the bronchial tree, lodging in
described in people and include ground‐glass, unstruc- small‐caliber distal airways and initiating a bacterial
tured interstitial, and centrilobular nodular interstitial bronchopneumonia. CT features depend on acuity and
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