Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 67
Fig. 2-41 A 12-year-old spayed
mixed breed dog with a 1-month
history of coughing and gagging. A
lateral radiograph of the cervical trachea
was normal. The tracheal cartilages
are faintly visible. The diameter
of the cervical trachea is normal with
a slight narrowing of the lumen caudal
to the cricoid cartilage.
Diagnosis: Normal cervical trachea.
(mucosal) surface should be intact and smooth. A slight dorsal indentation may be present
immediately caudal to the cricoid cartilage but, in general, the dorsoventral tracheal diameter
should not be less than that of the larynx. 44 Flexion and extension of the head and neck
will alter the position of the trachea.
Identification of the cervical trachea is difficult on the ventrodorsal radiograph due to
superimposition of the vertebral column. Additionally, poor patient positioning will alter
the trachea’s location on this view.
C E RV I C A L E S O P H AG U S
The cervical esophagus should not be visible unless the animal swallows a bolus of air at
the time of the radiographic exposure. The area through which the esophagus passes
should be evaluated. The esophagus begins dorsal to the cricoid cartilage, remains dorsal
to the trachea, and gradually moves laterally and to the left at the midcervical area. It continues
to lie on the left side until it passes the thoracic inlet. The esophagus may be visible
as a soft-tissue density overlying the trachea through the midcervical area and beyond the
thoracic inlet. The appearance of superimposition is probably the result of the esophagus
indenting the trachea or actually resting in the groove for the trachealis muscle. This
appearance on lateral survey radiographs may indicate tracheal collapse, chondromalacia
of the tracheal cartilages, or a flaccid trachealis muscle.
RADIO GRAPHIC AND SONO GRAPHIC ABNORMALITIES
SOFT-TISSUE ABNORMALITIES
The soft-tissue structures of the neck, although not visible as individual structures, give the
appearance of longitudinal streaking parallel to the spine because of the fat in the fascial
planes between these predominately muscular structures. Soft-tissue abnormalities include
soft-tissue swelling and changes in density. The extent and location of the swelling are
important. Localized or defined soft-tissue swellings may be caused by tumors or localized
infections (i.e., abscess, granuloma). Diffuse soft-tissue swelling may result from subcutaneous
fluid administration, edema, hemorrhage, or cellulitis (i.e., diffuse infection). This
may appear as a loss of the normal linear streaking, normally due to the soft tissue and fat.
Extension of the soft-tissue swelling into the thoracic cavity or involvement of adjacent
bone provides important clues to the radiographic diagnosis. Oblique radiographs may be
necessary to detect pleural extension of an external mass.