Page 321 - Small Animal Internal Medicine, 6th Edition

CHAPTER 20 Diagnostic Tests for the Lower Respiratory Tract 293

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FIG 20.8
Lateral radiograph of a dog with pulmonary carcinoma. An unstructured pattern is
present, as is an increased bronchial pattern.

Lesions caused by parasites, fungal infections, and some
eosinophilic lung diseases or idiopathic interstitial pneumo­ BOX 20.6
nias may be indistinguishable from neoplastic lesions. In the Differential Diagnoses for Dogs and Cats With Reticular
absence of strong clinical evidence, malignant neoplasia (Unstructured) Interstitial Patterns
must be confirmed cytologically or histologically. If this is
not possible, radiographs can be obtained again 4 weeks later Pulmonary Edema (Mild)
to evaluate for progression of disease. Infection
Neoplastic involvement of the pulmonary parenchyma Viral pneumonia
cannot be totally excluded on the basis of thoracic radio­ Bacterial pneumonia
graph findings because malignant cells are present for a Toxoplasmosis
while before lesions reach a radiographically detectable size. Mycotic pneumonia
The sensitivity of radiography in identifying neoplastic Parasitic infection (more often bronchial or nodular
interstitial pattern)
nodules can be improved by obtaining left and right lateral Neoplasia
views of the thorax. Eosinophilic Lung Disease
The reticular interstitial pattern is characterized by a Idiopathic Interstitial Pneumonia
diffuse, unstructured, lacy increase in the opacity of the pul­ Idiopathic pulmonary fibrosis
monary interstitium, which partially obscures normal vas­ Hemorrhage (Mild)
cular and airway markings. Reticular interstitial patterns
frequently occur in conjunction with nodular interstitial pat­
terns (also called reticulonodular patterns) and alveolar and
bronchial patterns (Fig. 20.8). interstitial nodular patterns can cause a reticular interstitial
Increased reticular interstitial opacity can result from pattern early in the course of disease (see Boxes 20.4 and
edema, hemorrhage, inflammatory cells, neoplastic cells, or 20.5). This pattern is also often seen in older dogs with no
fibrosis within the interstitium (Box 20.6). The interstitial clinically apparent disease, presumably as a result of pulmo­
space surrounds the airways and vessels, and is normally nary fibrosis; this further decreases the specificity of the
extremely small in dogs and cats. With continued accumula­ finding.
tion of fluid or cells, however, the alveoli can become flooded,
which produces an alveolar pattern. Visible focal interstitial Lung Lobe Consolidation
accumulations of cells, or nodules, can also develop with Lung lobe consolidation is characterized by a lung lobe that
time. Any of the diseases associated with alveolar and is entirely of soft tissue opacity (Fig. 20.9, A). Consolidation