Page 319 - Small Animal Internal Medicine, 6th Edition

CHAPTER 20 Diagnostic Tests for the Lower Respiratory Tract 291

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FIG 20.4
Lateral radiograph of a dog with chronic bronchitis and bronchiectasis. The airway
lumens are greatly enlarged, and normal tapering of the airway walls is not seen.

BOX 20.4

Differential Diagnoses for Dogs and Cats With Alveolar
Patterns on Thoracic Radiographs*
Pulmonary Edema
Severe Inflammatory Disease
Bacterial pneumonia
Aspiration pneumonia
Hemorrhage
Pulmonary contusion
Pulmonary thromboembolism
Neoplasia
Fungal pneumonia
Systemic coagulopathy
FIG 20.5
*Any of the differential diagnoses for interstitial patterns (see Boxes Lateral view of the thorax of a dog with aspiration
20.5 and 20.6) can cause an alveolar pattern if associated with pneumonia. An alveolar pattern is evident by the increased
severe inflammation, edema, or hemorrhage. soft tissue opacity with air bronchograms. Air bronchograms
are bronchial air stripes without visible bronchial walls. In
this radiograph the pattern is most severe in the ventral
fluid­filled alveoli are silhouetted against the walls of the (dependent) regions of the lung, consistent with bacterial or
airways they surround. The result is a visible stripe of air aspiration pneumonia.
from the airway lumen in the absence of definable airway
walls. This stripe is an air bronchogram (Fig. 20.5). If fluid Edema most often results from left­sided heart failure (see
continues to accumulate, the airway lumen eventually will Chapter 22). In dogs the fluid initially accumulates in the
also become filled with fluid, resulting in the formation of perihilar region, and eventually the entire lung is affected. In
solid areas of fluid opacity, or consolidation. When fluid­ cats patchy areas of edema can be present initially through­
dense regions are located at the edge of the lung lobe, a lobar out the lung fields. The finding of enlarged pulmonary veins
sign occurs. The curvilinear edge of the affected lung lobe is supports the cardiac origin of the infiltrates. Noncardiogenic
visible in contrast with the adjacent, aerated lobe. edema is typically most severe in the caudal lung lobes.