Page 388 - Small Animal Internal Medicine, 6th Edition

360 PART II Respiratory System Disorders

CHAPTER 23
VetBooks.ir

Clinical Manifestations and

Diagnostic Tests of Pleural

Cavity and Mediastinal Disease

CLINICAL SIGNS stabilize the animal’s condition before radiographs are taken.
Although thoracocentesis is more invasive than radiography,
Common abnormalities of the pleural cavity in the dog and the potential therapeutic benefit of the procedure far out-
cat include the accumulation of fluid (pleural effusion) or air weighs the small risk of complications. Animals in stable
(pneumothorax) in the pleural space. Mediastinal masses and condition at presentation can be evaluated initially with tho-
the pneumomediastinum are also discussed in this chapter racic radiographs or ultrasound to confirm the presence of
and the next. Respiratory signs caused by pleural disease air or fluid and the location of fluid before thoracocentesis
result from interference with normal expansion of the lungs. is performed.
Exercise intolerance is an early sign; overt respiratory dis- Ultrasonography is a valuable tool for the evaluation
tress ultimately occurs. Physical examination findings that of patients with pleural effusion. If equipment is available
assist in localizing the cause of respiratory compromise to on site, animals in critical condition can be examined with
the pleural space include increased respiratory rate and minimal stress to confirm the presence of fluid and direct
decreased lung sounds on auscultation (see Chapter 25). needle placement for thoracocentesis. Ultrasonography is
With increasing compromise, increased abdominal excur- also useful in evaluating the thorax for the presence of mass
sions during breathing may be seen. Breathing effort may be lesions, hernias, and primary cardiac or pericardial disease.
increased during inspiration relative to expiration, but this Because sound waves cannot pass through aerated lungs,
finding is not always obvious. Paradoxical breathing refers any masses must be adjacent to the chest wall, heart, or dia-
to a breathing pattern in which the abdominal walls are phragm to be detected by ultrasound. The presence of pleural
“sucked in” during inspiration. Paradoxical breathing has fluid facilitates ultrasonographic evaluation of the chest. If
been associated with pleural diseases in dogs and cats pre- the patient is stable, it is preferable to evaluate the thorax
sented for respiratory distress (LeBoedec et al., 2012). In cats ultrasonographically before the pleural fluid is removed.
with mediastinal masses, decreased compressibility of the Thoracic radiographs should be taken again after as much
anterior thorax may be palpable. fluid or air as possible has been removed from the pleural
Pulmonary thromboembolism (PTE) can cause pleural space and the lungs have had time to reexpand. Full expan-
effusion. The effusion is generally mild and may be an sion of the lungs is required for accurate evaluation of the
exudate or a modified transudate. PTE should be consid- pulmonary parenchyma. The presence of fluid also obscures
ered as a diagnosis, particularly in patients whose respira- visibility of heart size and shape and mass lesions.
tory efforts seem in excess of the volume of effusion (see Cytologic analysis of pleural fluid obtained by thora-
Chapter 22). cocentesis is indicated for the diagnostic evaluation of all
animals with pleural effusion. Measurement of protein con-
centration and total nucleated cell count, as well as qualita-
GENERAL DIAGNOSTIC APPROACH tive assessment of individual cells, is essential for accurate
classification of the fluid, formulation of a diagnostic plan,
The presence of pleural or mediastinal disease in a dog or cat and initiation of appropriate therapy (Table 23.1). The diag-
is usually confirmed by thoracic radiography, thoracic ultra- nostic approach to patients with pleural effusion based on
sonography, or thoracocentesis. In animals presented in cytologic findings is described further later. For patients with
respiratory distress with suspected pleural effusion or pneu- a mediastinal mass, fine-needle aspirates are obtained with
mothorax, thoracocentesis is performed immediately to ultrasound guidance for analysis.

360