Page 363 - Small Animal Internal Medicine, 6th Edition

CHAPTER 21 Disorders of the Trachea and Bronchi 335

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FIG 21.5
Lateral radiograph of the thorax and neck of a dog with A
collapsing trachea taken during inspiration. The
extrathoracic airway stripe is severely narrowed cranial to
the thoracic inlet.

of the thorax should also be taken during inspiration to
detect concurrent bronchial or parenchymal abnormalities.
(See Chapter 20 for further discussion of radiography.) It
should be noted that the common radiographic finding of a
redundant dorsal tracheal membrane can be a result of over-
lying soft tissue (most likely esophagus) rather than from
TBM (Bylicki et al., 2015).
Fluoroscopic evaluation provides a “motion picture” view
of large airway dynamics, making changes in luminal diam-
eter easier to identify than by routine radiography. The sensi-
tivity of fluoroscopy in detecting airway collapse is enhanced
if the patient can be induced to cough during the evaluation B
by pressure applied to the trachea. Some degree of collapse
is probably normal during cough, and in people a diagno- FIG 21.6
sis of tracheobronchomalacia is generally made if luminal Lateral radiographs of a dog with tracheobronchomalacia.
diameter decreases by more than 70% during forced exhala- During inspiration (A) the trachea and mainstem bronchi
are nearly normal. During expiration (B) the intrathoracic
tion. This criterion was recently increased from 50% because trachea and mainstem bronchi are markedly narrowed.
studies in people have shown that a strong cough can result Evaluation of the pulmonary parenchyma should not be
in near total collapse in some apparently healthy individuals. attempted using films exposed during expiration.
Bronchoscopy is also useful in the diagnosis of airway
collapse (Fig. 21.7; see also Fig. 21.3). The bronchi of smaller
dogs may be difficult to evaluate by radiography or fluoros-
copy but are easily examined bronchoscopically. Bronchos-
copy and the collection of airway specimens (such as by BAL
and bronchial brushings) are useful for identifying exacer-
bating or concurrent conditions.
Bronchoscopy is performed with the patient under
general anesthesia, which interferes with the ability to induce
cough. However, allowing the patient to reach a light plane
of anesthesia while the airways are manipulated will often A B
cause more forceful respirations that increase the likelihood
of identifying airway collapse. FIG 21.7
Additional tests are performed to identify exacerbating Bronchoscopic images from a dog with tracheal collapse
or concurrent conditions. Tracheal wash fluid is analyzed by (A). The dorsal tracheal membrane is much wider than that
cytology and culture if bronchoscopy with specimen collec- of a normal dog (B). The airway lumen is greatly
tion is not done. Other considerations include upper airway compromised.