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Feline Pulmonary Disease
Martha M. Larson

Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, USA

14.1 Patterns of Disease walls are silhouetted by the alveolar opacity, and are not
visualized. A lobar sign results if the alveolar opacity
Using a traditional approach, the radiographic appearance extends to the lobe margin, causing a dramatic demarca-
of the lung can be divided into various components: alve- tion between the normal air‐filled lobe and the adjacent
oli, interstitial tissue, bronchial walls, and vessels diseased lobe (Figures 14.2–14.4). The lobar sign may not
(Figure 14.1). Changes in pulmonary opacity can be classi- be visualized if it is not struck tangentially by the X‐ray
fied into one of four patterns: alveolar, interstitial, bron- beam, or if the disease process does not extend to the lobe
chial, and vascular. Most diseases involve more than one margin. The alveolar pattern is termed consolidation, using
parenchymal component (mixed pattern), but one pattern the nontraditional terminology (increased lung opacity,
usually predominates. with maintained volume, that results in border effacement
A nontraditional approach is becoming increasingly of adjacent heart or diaphragm). The most common dis-
popular, and uses terminology that does not involve spe- eases that result in an alveolar pattern include pneumonia,
cific anatomic terms. This newer approach determines if edema, and hemorrhage.
an increased lung opacity results in a smaller lung volume
or normal/increased size. The increased opacity is called 14.1.2 Atelectasis
consolidated if the opacity results in border effacement (sil-
houette effect) or ground‐glass if the opacity does not sil- Atelectasis, or collapse of a lung lobe, results in an alveolar
houette with adjacent structures. Increased prominence of pattern due to loss of the alveolar air. However, the air is
the bronchial walls/interstitium is termed bronchocentric not replaced, resulting in a loss of lung volume. The medi-
in an effort to avoid discriminating between microscopic astinum will shift toward the side of the abnormal (col-
anatomy. lapsed) lung to compensate for the loss of volume. This is
typically noted by shifting of the heart, the largest organ in
the mediastinum (Figure 14.5). Atelectasis can be tran-
14.1.1 Alveolar Pattern sient, secondary to prolonged recumbency. Pathologic

In this pattern, the air in the alveoli is removed and replaced causes include obstruction of the airways by mucus, for-
by fluid/cells. The increased pulmonary opacity is homoge- eign body, or mass. Iatrogenic tracheal intubation beyond
neous and uniform in appearance, with varying degrees of the carina, into a main bronchus, will result in collapse of
opacity, depending on the degree and severity of the alveo- the contralateral lung.
lar filling. With an alveolar pattern, the opacity of the lung
is more intense than any other pattern. Silhouette effect 14.1.3 Interstitial (Unstructured/Linear)
(border effacement) results if the opacity is severe enough Pattern
and is in close anatomic contact with the heart or dia-
phragm. Air bronchograms are created by air‐filled bronchi In this pattern, the interstitial tissue becomes thickened by
extending through the increased lobe opacity, and demon- fluid and/or cells. The resulting increase in opacity is not
strate radiolucent tubular, branching structures. Bronchial as dramatic or severe as the alveolar pattern, but instead

Feline Diagnostic Imaging, First Edition. Edited by Merrilee Holland and Judith Hudson.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.