Page 391 - Small Animal Internal Medicine, 6th Edition

CHAPTER 23 Clinical Manifestations and Diagnostic Tests of Pleural Cavity and Mediastinal Disease 363

to intraperitoneally administer water-soluble iodinated con- secondary to migrating grass awns or other foreign bodies,
trast media and perform peritoneography, or perform CT, to or as an extension of bacterial pneumonia. Sterile technique
VetBooks.ir confirm the presence of a diaphragmatic hernia. should be used during thoracocentesis and chest tube place-
Neoplasia must be considered as a differential diagnosis
ment in all animals with pleural effusion or pneumothorax,
for patients with any type of effusion, although it is rare for
Gram staining and both aerobic and anaerobic bacte-
a pure transudate to develop. (See the section on effusions to prevent iatrogenic infection.
caused by neoplasia.) rial cultures with antibiotic sensitivity testing should be
performed on the fluid. Prolonged incubation should be
SEPTIC AND NONSEPTIC EXUDATES requested to increase the likelihood of identifying Acti-
Exudates have a high protein concentration (greater than nomyces and Nocardia spp. Culture and sensitivity testing
3 g/dL) compared with that in transudates. Nucleated cell provide valuable information that can be used in selecting
counts are also high (greater than 5000/µL). Cell types in appropriate antibiotics and in monitoring therapy. Mixed
nonseptic exudates include neutrophils, macrophages, bacterial infections are common. However, bacteria do not
eosinophils, and lymphocytes. The macrophages and lym- grow from cultures of all septic exudates, and results are not
phocytes may be activated, and typically the neutrophils are available for several days. Gram staining provides immediate
nondegenerative. There is no evidence of organisms. Dif- information that can be used to help select antibiotics and
ferential diagnoses in animals with nonseptic exudates is helpful in cases in which bacteria cannot be grown from
include feline infectious peritonitis (FIP), neoplasia, chronic the fluid.
diaphragmatic hernia, lung lobe torsion, and resolving septic
exudates. Prior treatment with antibiotics in animals with a CHYLOUS EFFUSIONS
septic effusion can alter the characteristics of the neutrophil Chylous effusion (chylothorax) results from leakage of fluid
population in the fluid, making them appear nondegenera- from the thoracic duct, which carries lipid-rich lymph from
tive, and can decrease the number of organisms present in the body. Such leakage can be idiopathic or congenital,
the fluid to an undetectable level. Therefore pleural fluid or it can occur secondary to trauma, neoplasia, cardiac
analysis should be performed before treatment is initiated so disease, pericardial disease, dirofilariasis, lung lobe torsion,
that bacterial infection is not overlooked. or diaphragmatic hernia. Chyle is usually milky white and
Cats with FIP can present with fever or chorioretinitis in turbid (see Fig. 23.1, E), largely as a result of chylomicrons
addition to respiratory signs (see Chapter 96). The pleural that carry fats from the intestines. The fluid is occasion-
fluid protein concentration is often very high in such animals, ally blood tinged, although this finding may be an artifact
approaching serum concentrations. It is common to see from prior thoracocentesis. It is possible to obtain clear and
fibrin strands or clots in the fluid. Careful cytologic evalua- colorless fluids, particularly in anorectic animals, but this is
tion of the fluid is essential to differentiate FIP fluid from uncommon.
exudates caused by pyothorax or malignant lymphoma. Chyle has the cytologic characteristics of a modified tran-
Evaluation of animals for diaphragmatic hernia was described sudate or nonseptic exudate with moderate concentrations
for transudates, and evaluation for neoplasia is discussed of protein, usually greater than 2.5 g/dL. The nucleated cell
later in the section titled Effusion Caused by Neoplasia. count is low to moderate, ranging from 400 to 10,000/µL.
Spontaneous lung lobe torsions are most common in dogs Early in the disease, the predominant cell type is the small
with deep, narrow thoracic cavities. In addition to causing lymphocyte. A few neutrophils may also be present. With
an effusion, torsions can be seen in dogs and cats secondary time, nondegenerative neutrophils become more predomi-
to pleural effusion. Underlying pulmonary disease resulting nant, and lymphocytes are fewer. Macrophages also increase
in lobe atelectasis can also contribute to the development of in number with time, and plasma cells may be present.
torsion. Torsion should be considered in animals with a pre- A diagnosis of chylothorax is confirmed by measuring the
existing effusion or pulmonary disease if their condition concentrations of triglycerides in pleural fluid and serum.
suddenly deteriorates. The effusion is often a nonseptic Each specimen should be well mixed by the laboratory
exudate, but it may be chylous or hemorrhagic. Signs of lung before a portion is analyzed because of the tendency for the
lobe torsion may be identified through thoracic radiography lipid portion to rise to the surface. The triglyceride content
or ultrasonography (see Chapter 20). CT, bronchoscopy, or in chyle is high compared with that in serum. Rarely, the test
thoracotomy is required to verify the condition in some will need to be repeated after a meal in anorectic animals.
animals. Most cases of chylothorax are idiopathic, but this diagno-
Septic exudates often have extremely high nucleated cell sis can be made only after other disorders have been ruled
counts (e.g., 50,000 to more than 100,000/µL), and degener- out. Treatment is most likely to be successful if an underlying
ate neutrophils are the predominant cells. Bacteria can often problem is identified and treated directly. (See Chapter 24
be observed within neutrophils and macrophages as well as for a complete discussion of chylothorax.)
extracellularly (see Fig. 24.1). The fluid may have a foul odor.
Septic exudates are diagnostic for pyothorax, which can HEMORRHAGIC EFFUSIONS
occur spontaneously, secondary to wounds that penetrate Hemorrhagic effusions are grossly red as a result of the large
into the thoracic cavity through the chest wall or esophagus, red blood cell content. Hemorrhagic effusions consist of more