Page 380 - Small Animal Internal Medicine, 6th Edition

352 PART II Respiratory System Disorders

within weeks of onset of signs, and only 7 of 23 survived Some animals with lung neoplasia have no clinical signs
longer than 1 year (Cohn et al., 2004). at all, and the tumor is discovered as an incidental finding
VetBooks.ir PULMONARY NEOPLASIA on thoracic radiographs or at postmortem examination.
Animals with metastatic or multicentric lung neoplasia may
have signs of tumor involvement in another organ.
Lung sounds may be normal, decreased, or increased.
Primary pulmonary tumors, metastatic neoplasia, and mul- They are decreased over all lung fields in animals with pneu-
ticentric neoplasia can involve the lungs. Most primary pul- mothorax or pleural effusion. Localized decreased or
monary tumors are malignant. Carcinomas predominate increased lung sounds can be heard over regions that are
and include adenocarcinoma, bronchoalveolar carcinoma, consolidated. In a few patients, crackles and wheezes can be
and squamous cell carcinoma. Sarcomas and benign tumors auscultated. Evidence of other organ involvement or hyper-
are much less common. Small cell carcinoma, or oat cell trophic osteopathy may be noted.
tumor, which occurs frequently in people, is rare in dogs and
cats. Diagnosis
The lungs are a common site for the metastasis of malig- Neoplasia is definitively diagnosed through the histologic or
nant neoplasia from other sites in the body and even from cytologic identification of criteria of malignancy in popula-
primary pulmonary tumors. Neoplastic cells can be carried tions of cells in pulmonary specimens (Fig. 22.5). Thoracic
in the bloodstream and trapped in the lungs, where low radiographs are commonly evaluated initially, and findings
blood flow and an extensive capillary network are present. can support a tentative diagnosis of neoplasia. Radiographs
Lymphatic spread or local invasion can also occur. can be used to identify the location of disease; this informa-
Multicentric tumors can involve the lungs. Such tion helps the clinician select the most appropriate technique
tumors include lymphoma, malignant histiocytosis, and for specimen collection.
mastocytoma. Good-quality radiographs, including both left and right
Multiple tumors of different origins can occur in the same lateral projections, should be evaluated. Primary pulmonary
animal. In other words, the presence of a neoplasm in one tumors can cause localized mass lesions (see Figs. 20.7 and
site of the body does not necessarily imply that the same 20.10) or the consolidation of an entire lobe (see Fig. 20.9,
tumor is also present in the lungs. A). Tumor margins are often distinct but can be ill defined
as a result of associated inflammation and edema. Cavitation
Clinical Features may be evident. Metastatic or multicentric disease results in
Neoplasms are most common in older animals but also a diffuse reticular, nodular, or reticulonodular interstitial
occur in young adult animals. Tumors involving the lungs
can produce a wide spectrum of clinical signs. These signs
are usually chronic and slowly progressive, but peracute
manifestations such as pneumothorax or hemorrhage can
occur.
Most signs reflect respiratory tract involvement. Infiltra-
tion of the lung by the tumor can cause interference with
oxygenation, leading to increased respiratory effort and exer-
cise intolerance. Mass lesions can compress airways, provok-
ing cough and obstructing ventilation. Erosion through
vessels can result in pulmonary hemorrhage. Blood loss can
be sudden, resulting in acute hypovolemia and anemia, in
addition to respiratory compromise. Edema, nonseptic
inflammation, or bacterial infection can occur secondary to
the tumor. Erosion through the airways can result in pneu-
mothorax. Pleural effusion of nearly any character can form.
In rare cases, the caudal or cranial venae cavae are obstructed,
resulting in the development of ascites or head and neck FIG 22.5
edema, respectively. Bronchoalveolar lavage fluid from the dog whose lateral
Nonspecific signs in dogs and cats with pulmonary neo- thoracic radiograph showing a severe, unstructured
plasms include weight loss, anorexia, depression, and fever. interstitial pattern is depicted in Fig. 20.8. Many clumps of
Gastrointestinal signs may be the primary complaint. Vomit- deeply staining epithelial cells showing marked criteria of
ing and regurgitation may be the presenting signs in cats in malignancy were seen. One such clump is shown here. A
diagnosis of carcinoma was made. Note that a cytologic
particular. Lameness may be the presenting sign in patients diagnosis of carcinoma should not be made if concurrent
with hypertrophic osteopathy secondary to thoracic mass inflammation is noted. The surrounding lighter-staining cells
lesions and in cats with metastasis of carcinoma to their are alveolar macrophages—the normal predominant cell
digits. type in bronchoalveolar lavage fluid.