Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 113
A
Fig. 2-89 A 14-year-old male
Cocker Spaniel with a history of
chronic cough for several months. A,
On the lateral radiographs taken on
inspiration the trachea appears of
normal size. B, On the lateral radiograph
taken at expiration the trachea
narrows markedly at the
tracheal bifurcation. This is indicative
of collapse of the tracheal bifurcation
and main stem bronchi.
Enlargement of the left ventricle and
left atrium is present. The left atrium
is seen extending caudal and dorsal
to the tracheal bifurcation (arrows).
Diagnosis: Collapse of the tracheal
bifurcation and main stem bronchi.
Left heart enlargement consistent
with mitral valve insufficiency.
B
A tangential cross-sectional projection of the trachea also has been described for evaluation
of tracheal collapse. The animal is positioned in sternal recumbency and the head and
neck are dorsiflexed. The x-ray beam is directed caudally and ventrally to strike the trachea
tangentially at the thoracic inlet. Although this view is difficult to obtain because of patient
resistance, it may provide additional information (Fig. 2-90).
The amount of tracheal collapse that occurs during coughing in normal dogs has not
been defined. A clear-cut distinction between normal narrowing and tracheal collapse cannot
be made. If the tracheal diameter narrows more than 50% with normal respiration or
coughing, a diagnosis of tracheal collapse should be considered. If the tracheal diameter
narrows by more than 20% in normal respiration, a diagnosis of tracheal collapse should
be considered if clinical signs are present.
An overlap of the trachea by the esophagus at the thoracic inlet may be seen.
Careful examination of the radiograph will reveal the tracheal lucency with the superimposed
esophagus. This is probably due to a flaccid dorsal trachealis muscle with
esophageal indentation (see Fig. 2-90). The trachea may rotate slightly, causing the trachealis
muscle to become dorsolateral instead of dorsal. Indentation of the trachea by
the esophagus due to laxity of the trachealis muscle may represent a type of collapsing
trachea.
Animals with tracheal collapse also may have cardiac, pulmonary, or bronchial disease;
therefore the radiographic evaluation should include the entire respiratory tract. Tracheal
collapse occurs most frequently in old, obese, small-breed dogs. It rarely occurs in cats. 205
ESOPHAGEAL ABNORMALITIES
Radiography is an important part of the clinical evaluation of animals with esophageal
abnormalities. Survey radiographs provide useful information. Additional information can
be obtained with esophageal contrast studies. A static (radiographic) contrast examination
provides some functional information. However, a complete functional evaluation requires