Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

222 Small Animal Radiolo g y and Ultrasono graphy
P U L M O N A RY B U L L A E A N D B L E B S
Pulmonary bullae and blebs produce oval, round, or spherical radiolucent areas with a
thin, smooth, tissue-dense margin (Fig. 2-206). They may be congenital or secondary to
trauma or infection. 631 Their smooth, thin walls distinguish them from other cavitary
lesions. Although the term bulla usually indicates a lesion within the lung and the term bleb
usually indicates a subpleural lesion, the terms often are used interchangeably.
Pneumomediastinum or pneumothorax may occur as a sequela to rupture of bullae or
blebs. Many traumatic bullae contain both air and fluid. A radiograph obtained using a
horizontal x-ray beam may demonstrate the air–fluid interface. Computed tomography
has been used to demonstrate bullae that were not apparent on survey radiography. 73
C AV I TA RY L E S I O N S
A tissue-dense mass within the lung may become necrotic and communicate with an airway,
allowing air accumulation within the mass and producing a cavitary
lesion. 632,633,635,637-643 Cavitation may occur with primary and secondary neoplasms, granulomas,
congenital bronchial cysts, and intrapulmonary abscesses (Figs. 2-207 to 2-209).
Cavitary lesions generally have thicker, more irregular walls than bullae or blebs. It is nearly
impossible to differentiate the cause of the cavitary lesion based solely on its radiographic
features.
E M P H Y S E M A
Focal areas of emphysema are uncommon and usually are accompanied by chronic
bronchial and interstitial disease (Fig. 2-210). They often are masked by the increased pulmonary
density, which results from the bronchial or interstitial infiltrate. Chronic bronchitis
and bronchiectasis may result in focal emphysematous areas.
Generalized emphysema, deep inspiration, and overinflation result in similar radiographic
changes. The diaphragm appears flattened and the dome is positioned caudally
to approximately the level of T13 or L1. The cardiac silhouette often appears small. The
lungs appear hyperlucent with well-defined and small pulmonary vessels. Bronchial structures
may appear normal, reduced, or increased in number, size, or wall thickness.
Radiographs should be obtained at both full inspiration and expiration when generalized
Fig. 2-206 Radiographs of a
2-year-old female mixed breed dog
were performed after thoracic
trauma. The dog showed evidence of
mild respiratory distress. On the lateral
thoracic radiograph there is a
fluid- and air-filled structure evident
and superimposed on the cardiac silhouette
(arrows). The structure has
thin, soft tissue–dense walls. The cardiac
silhouette is separated from the
sternum. The left caudal lung lobe is
separated from the thoracic vertebral
bodies by an air density. Diagnosis:
Traumatic bulla and pneumothorax.