Page 318 - Small Animal Internal Medicine, 6th Edition

290 PART II Respiratory System Disorders

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FIG 20.3
A bronchointerstitial pattern is present in this lateral radiograph from a cat with idiopathic
bronchitis. The bronchial component results from thickening of the bronchial walls and is
characterized by “doughnuts” and “tram lines.” In this radiograph, the bronchial changes
are most apparent in the caudal lung lobes.

stenosis may also cause radiographically visible undercircu­
lation in some dogs. Hyperinflation is associated with BOX 20.3
obstructive airway disease, such as allergic or idiopathic Differential Diagnoses for Dogs and Cats With Bronchial
feline bronchitis.
Patterns on Thoracic Radiographs*
Bronchial Pattern Canine chronic bronchitis
Bronchial walls are most easily discernible at the hilus on Feline bronchitis (idiopathic)
radiographs of normal dogs and cats. They should taper and Allergic bronchitis
grow thinner as they extend toward the periphery of each Canine infectious respiratory disease complex
lung lobe. Bronchial structures are not normally visible Bacterial infection
radiographically in the peripheral regions of the lungs. The Mycoplasmal infection
cartilage may be calcified in older dogs and in chondrodys­ Pulmonary parasites
trophic breeds, making the walls more prominent but still *Bronchial disease can occur in conjunction with parenchymal lung
sharply defined. disease. See Boxes 20.4 to 20.6 for additional differential
Thickening of the bronchial walls or bronchial dilation diagnoses if mixed patterns are present.
results in a bronchial pattern. Thickened bronchial walls are
visible as “tram lines” and “doughnuts” in the peripheral
regions of the lung (Fig. 20.3). Tram lines are produced by identified radiographically by the presence of widened, non­
airways that run transverse to the X­ray beam, causing the tapering airways (Fig. 20.4). Bronchiectasis can be cylindri­
appearance of parallel thick lines with an air stripe in cal (tubular) or saccular (cystic). Cylindrical bronchiectasis
between. Doughnuts are produced by airways that are point­ is characterized by fairly uniform dilation of the airway.
ing directly toward or away from the beam, causing a thick Saccular bronchiectasis additionally has localized dilations
circle to be seen radiographically, with the airway lumen peripherally that can lead to a honeycomb appearance. All
creating the “hole.” The walls of the bronchi tend to be indis­ major bronchi are usually affected, though localized disease
tinct. The finding of thickened walls indicates the presence can occur.
of bronchitis and results from an accumulation of mucus or
exudate along the walls within the lumens, an infiltration of Alveolar Pattern
inflammatory cells within the walls, muscular hypertrophy, Alveoli are not normally visible radiographically. Alveolar
epithelial hyperplasia, or a combination of these changes. patterns occur when the alveoli are filled with fluid­dense
Potential causes of bronchial disease are listed in Box 20.3. material. The fluid opacity may be caused by edema, inflam­
Chronic bronchial inflammation can result in irreversible mation, hemorrhage, or neoplastic infiltrates, which gener­
dilation of the airways, which is termed bronchiectasis. It is ally originate from the interstitial tissues (Box 20.4). The