Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 183
VA S C U L A R PAT T E R N S
Vascular patterns are produced by an increase or decrease in the size, shape, and number
of pulmonary arteries and veins. Evaluation of pulmonary vascular size is subjective, based
on a recollection of other similar-sized patients. Semiquantitative methods of assessing
lobar vessel size have been described. 72 Vessels radiographically appear as linear, tapering,
branching, soft tissue–dense structures that parallel the course of the main lobar airways.
When vessels branch perpendicular to the x-ray beam, they are seen as distinct round, solid
densities that have the same or slightly smaller diameter than the parent vessel. The margins
of the pulmonary vessels should be smooth and well defined. Vascular patterns without
other pulmonary patterns rarely are observed in pulmonary diseases but may be
observed in animals with cardiovascular disease.
D I F F E R E N T I A L D I AG N O S E S U S I N G P U L M O N A RY PAT T E R N S
In addition to the symmetry, distribution, and pattern of a pulmonary lesion, changes in
other thoracic structures should be noted and used to narrow the differential diagnosis.
The presence or absence of cardiac, lymph node, tracheal, esophageal, diaphragm, rib, or
chest wall lesions will influence the probability of a specific diagnosis. However, in many
cases only a ranking of differential diagnoses is possible. Pattern recognition provides useful
clues in differentiating pulmonary diseases. In many cases, a mixture of patterns is
observed. In those cases, the predominant pattern should be used to classify the density
observed. 502 A classic example of this is the pathogenesis of left heart failure. In the early
stages of congestive heart failure, an increased vascular pattern is present. This is followed
by an interstitial pattern with loss of vascular outlines. Finally, this may progress to an alveolar
pattern of infiltrates, with loss of both vascular and bronchial wall shadows, coalescing
fluffy densities, and possibly air bronchograms. Although many different pulmonary
diseases can demonstrate various patterns during the course of disease, most diseases have
typical infiltrate patterns at the time they are evaluated radiographically. For example, bacterial
pneumonia usually has a focal alveolar pattern when first seen, although interstitial
patterns will be visible very early in the disease and when the infiltrate has nearly resolved.
Recognition of the pattern and its distribution may suggest certain diagnoses, eliminate
others, and generally narrow the list of probable diagnoses (Table 2-2).
Fig. 2-165 A 2-year-old male mixed
breed dog was brought for evaluation
of a 3-week history of a cough.
On the lateral thoracic radiograph,
the pulmonary vessels are obscured
by a diffuse increase in pulmonary
densities. Several end-on bronchi
and thickened bronchial walls are
evident (arrows). The radiographic
findings indicate a diffuse bronchial
pattern and a mild interstitial pattern.
Diagnosis: Eosinophilic bronchitis
and pneumonitis. A
transtracheal wash was performed
and eosinophils were identified in
the specimen. The dog was treated
with glucocorticoids and the pulmonary
disease resolved.