Page 320 - Small Animal Internal Medicine, 6th Edition

292 PART II Respiratory System Disorders

Inflammatory infiltrates can be caused by infectious can form as a result of foreign bodies or as a sequela to bacte­
agents, noninfectious inflammatory disease, or neoplasia. rial pneumonia. Nodular patterns may also be seen on the
VetBooks.ir The location of the infiltrative process can often help estab­ radiographs obtained in animals with some eosinophilic
lung diseases and idiopathic interstitial pneumonias.
lish a tentative diagnosis. For example, diseases of airway
Inflammatory nodules can persist as inactive lesions after
origin, such as most bacterial and aspiration pneumonias,
primarily affect the dependent lung lobes (i.e., the right the disease resolves. In contrast to active inflammatory
middle and cranial lobes and the left cranial lobe). In con­ nodules, however, the borders of inactive nodules are often
trast, diseases of vascular origin, such as dirofilariasis, well demarcated. Nodules may become mineralized in some
thromboemboli, systemic fungal infection, and bacterial conditions, such as histoplasmosis. Well­defined, small,
infection of hematogenous origin primarily affect the caudal inactive nodules are sometimes seen in healthy older dogs
lung lobes. Localized processes involving only one lung lobe without a history of disease. Radiographs taken several
suggest the presence of a foreign body, neoplasia, abscess, months later in these animals typically show no change in
granuloma, or lung lobe torsion. the size of these inactive lesions.
Hemorrhage usually results from trauma. Thromboem­ Neoplastic nodules may be singular or multiple (Fig.
bolism, neoplasia, coagulopathies, and fungal infections can 20.7). They are often well defined, although secondary
also cause hemorrhage into the alveoli. inflammation, edema, or hemorrhage can obscure the
margins. No radiographic pattern is diagnostic for neoplasia.
Interstitial Pattern
The pulmonary interstitial tissues confer a fine, lacy pattern
to the pulmonary parenchyma of many dogs and cats as they
age, in the absence of clinically apparent respiratory disease.
They are not normally visible on inspiratory radiographs in
young adult animals.
Abnormal interstitial patterns are reticular (unstruc­
tured), nodular, or reticulonodular in appearance. A nodular
interstitial pattern is characterized by the finding of roughly
circular, fluid­dense lesions in one or more lung lobes.
However, the nodules must be nearly 1 cm in diameter to be
routinely detected. Interstitial nodules may represent active
or inactive inflammatory lesions or neoplasia (Box 20.5).
Active inflammatory nodules often have poorly defined
borders. Mycotic infections typically result in the formation
of multiple, diffuse nodules. The nodules may be small
(miliary; Fig. 20.6) or large and coalescing. Parasitic granu­ FIG 20.6
lomas are often multiple, although paragonimiasis can result Lateral view of the thorax in a dog with blastomycosis. A
in the formation of a single pulmonary nodule. Abscesses miliary, nodular interstitial pattern is present. Increased soft
tissue opacity above the base of the heart may be the result
of hilar lymphadenopathy.

BOX 20.5
Differential Diagnoses for Dogs and Cats With Nodular
Interstitial Patterns
Neoplasia
Mycotic Infection
Blastomycosis
Histoplasmosis
Coccidioidomycosis
Pulmonary Parasites
Aelurostrongylus infection
Paragonimus infection
Abscess
Bacterial pneumonia
Foreign body FIG 20.7
Eosinophilic Lung Disease Lateral view of the thorax of a dog with malignant
Idiopathic Interstitial Pneumonia neoplasia. A well-circumscribed, solid, circular mass is
Inactive Lesions present in the caudal lung field. Papillary adenocarcinoma
was diagnosed after surgical excision.