Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

106 Small Animal Radiolo g y and Ultrasono graphy
Fig. 2-79 A 2-year-old female cat with a unknown history of multiple external wounds and subcutaneous
emphysema. On the lateral radiograph, gas is noted in the soft tissues at the thoracic inlet.
The air dissects into the cranial mediastinum. The outer tracheal wall is distinctly outlined (open
arrows). The cranial vena cava and the aortic arch also are outlined distinctly (closed arrows). The azygous
vein is delineated clearly. There are multiple shotgun pellets in the soft tissues over the thorax.
Diagnosis: Pneumomediastinum. This resulted from extension of the subcutaneous emphysema
from the external wounds in the cervical soft tissues. There was no evidence of tracheal or esophageal
perforation. The mediastinal air resolved without treatment.
Localized or segmental tracheal stenosis may be congenital, secondary to local
inflammation and fibrosis, or secondary to trauma (Figs. 2-82 and 2-83). The stenosis is
usually circumferential and involves one or more tracheal rings. The mucosal surface is
usually smooth, although the tracheal rings may be deformed. Distinction between
acquired and congenital localized tracheal stenosis is not radiographically possible.
However, congenital localized stenosis is extremely uncommon. The major distinction
must be made between localized stenosis and intramural or intraluminal masses.
T R AC H E A L AV U L S I O N O R P E R F O R AT I O N
Tracheal avulsion or rupture is usually traumatic. 192,193 An interruption in the tracheal wall
may be visible (Fig. 2-84). The avulsed ends may be separated widely, or a thin, soft tissue–dense
band or line may separate the avulsed portions. Pneumomediastinum is frequently,
but not always, present.
Tracheal perforation is rarely a specific radiographic diagnosis. Pneumomediastinum is
often present, but the site of the perforation rarely can be identified even when contrast
studies are performed. 194
T R AC H E A L M A S S E S
Extraluminal masses may displace or deform the trachea. These usually arise from mediastinal
structures and are described in that section (see Mediastinal Structures). Because the trachea
is somewhat rigid, extraluminal masses produce a gradually curving displacement of the
trachea. Although displacement is the most common finding with an extraluminal mass, the
tracheal lumen can become narrowed if the mass surrounds the trachea or compresses it
against a solid structure such as the heart, aorta, spine, or cervical muscles. 195-197
Intramural lesions cause thickening of the tracheal wall with luminal deformities.
The curvature of the mass will be more abrupt than the gradual curve of the trachea,
which accompanies extraluminal masses. The degree of tracheal displacement depends
upon the amount of the mass that extends outside the tracheal wall and the compressibility
of the adjacent tissues. The mucosal surface of the trachea is usually smooth
(Figs. 2-85 and 2-86).
Intraluminal lesions are more common than intramural lesions. Granulomas, neoplasms,
polyps, and foreign objects may be encountered. Masses may be solitary or multiple
and are often eccentric. They produce rounded or cauliflower-shaped densities within the
tracheal lumen. The attachment site of the mass blends with the normal tracheal mucosa.