Page 338 - Small Animal Internal Medicine, 6th Edition

310 PART II Respiratory System Disorders

mean values. In our canine studies we have used values of supportive of the diagnosis in an additional 50%. Only
≥12% neutrophils, 14% eosinophils, or 16% lymphocytes dogs in which a definitive diagnosis was obtained by any
VetBooks.ir as indicative of inflammation. means were included. Definitive diagnoses were possible
Interpretation of BAL fluid cytology and cultures is essen­
on the basis of BAL only in those animals in which infec­
tially the same as that described for tracheal wash fluid,
overtly malignant cells were present in specimens in the
although the specimens are more representative of the deep tious organisms were identified, or in those cases in which
lung than the airways. In addition, the normal cell popula­ absence of marked inflammation. BAL has been shown to
tion of macrophages must not be misinterpreted as being be more sensitive than radiographs in identifying pulmonary
indicative of macrophagic or chronic inflammation (Fig. involvement with lymphosarcoma. Carcinoma was defini­
20.25). As for all cytologic specimens, definitive diagnoses tively identified in 57% of cases, and other sarcomas were
are made through identification of organisms or abnormal not found in BAL fluid. Fungal pneumonia was confirmed
cell populations. Fungal, protozoal, or parasitic organisms in only 25% of cases, although organisms were found in
may be present in extremely low numbers in BAL specimens; 67% of cases in a previous study of dogs with overt fungal
therefore the entire concentrated slide preparation must be pneumonia.
carefully scanned. Profound epithelial hyperplasia can occur
in the presence of an inflammatory response and should not
be confused with neoplasia. TRANSTHORACIC LUNG ASPIRATION
If quantitative bacterial culture is available, growth of AND BIOPSY
3
organisms at greater than 1.7 × 10 colony­forming units
(CFUs)/mL has been reported to indicate infection (Peeters Indications and Complications
et al., 2000). In the absence of quantitative numbers, growth Pulmonary parenchymal specimens can be obtained by
of organisms on a plate directly inoculated with BAL fluid is transthoracic needle aspiration or biopsy. Although only a
considered significant, whereas growth from fluid that small region of lung is sampled by these methods, collection
occurs only after multiplication in enrichment broth may be can be guided by radiographic findings or ultrasonography
a result of normal inhabitants or contamination. Patients to improve the likelihood of obtaining representative speci­
that are already receiving antibiotics at the time of specimen mens. As with tracheal wash and BAL, a definitive diagnosis
collection may have significant infection with few or no bac­ will be possible in patients with infectious or neoplastic
teria by culture. disease. Patients with noninfectious inflammatory diseases
require thoracoscopy or thoracotomy with lung biopsy for a
DIAGNOSTIC YIELD definitive diagnosis.
A retrospective study of BAL fluid cytologic analysis in dogs Potential complications of transthoracic needle aspiration
at referral institutions showed that BAL findings served as or biopsy include pneumothorax, hemothorax, and pulmo­
the basis for a definitive diagnosis in 25% of cases and were nary hemorrhage. These procedures are not recommended
in animals with suspected cysts, abscesses, pulmonary
hypertension, or coagulopathies. Severe complications are
uncommon, but these procedures should not be performed
unless the clinician is prepared to place a chest tube and
otherwise support the animal if necessary.
Lung aspirates and biopsy specimens are indicated for the
nonsurgical diagnosis of intrathoracic mass lesions that are
in contact with the thoracic wall. The risk of complications
in these animals is relatively low because the specimens can
be collected without disrupting aerated lung. Obtaining aspi­
rates or biopsy specimens from masses that are far from the
body wall and near the mediastinum carries the additional
risk of lacerating important mediastinal organs, vessels, or
nerves. If a solitary localized mass lesion is present, thora­
cotomy and biopsy should be considered rather than trans­
thoracic sampling because this permits both the diagnosis of
the problem and the potentially therapeutic benefits of com­
plete excision.
Transthoracic lung aspirates can be obtained in animals
with a diffuse interstitial radiographic pattern. In some of
these patients, solid areas of infiltrate in lung tissue immedi­
FIG 20.25 ately adjacent to the body wall can be identified ultrasono­
Bronchoalveolar lavage fluid from a normal dog. Note that graphically even though they are not apparent on thoracic
alveolar macrophages predominate. radiographs (see Fig. 20.11). Ultrasound guidance of the