Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Two The Thorax 197
Fig. 2-177 A 4-year-old male
Afghan Hound was evaluated for a
sudden onset of dyspnea.
Auscultation revealed dull lung
sounds in the left cranial thorax.
Examination of the lateral radiograph
reveals a homogeneous density
in the cranial lung lobe area.
Close examination reveals an abrupt
obstruction of the left cranial lung
lobe bronchus (arrow). Diagnosis:
Torsion of the left cranial lung lobe.
AT E L E C TA S I S
Atelectasis is collapse of a lung lobe. This occurs when the end–air spaces are no longer
filled with air, and it results in the affected lobe being homogeneously tissue dense with a
loss of normal volume. 561 Mediastinal shifts and compensatory hyperinflation of other
lung lobes may be noted in association with atelectasis. Complete atelectasis will not have
any air-filled structures and air bronchograms may not be present. There seems to be a
predilection for atelectasis of the right middle lung lobe in cats. The cause of this is
unknown. The general causes of atelectasis include airway obstruction due to tumor,
hypertrophy of luminal epithelium, or foreign matter; compression as seen with tumor,
hydrothorax, or hypostatic congestion; or pneumothorax evidenced by loss of negative
pleural pressure resulting in collapse of a lobe or lobes (Figs. 2-67 and 2-178).
DISEASES ASSOCIATED WITH INTERSTITIAL PATTERNS
These diseases may become apparent as a primarily linear-reticular or nodular pattern.
Although overlap frequently exists among these diseases, and even some overlap exists
between alveolar and interstitial patterns, the feature that is demonstrated most frequently
on the radiograph is the one that should be used in developing a list of possible diagnoses.
Disseminated or diffuse interstitial pulmonary patterns may be subdivided into
chronic or active infiltrates. In chronic interstitial patterns, the linear and circular densities
will be thin and fairly well defined, and the pulmonary vessel margins will be minimally
blurred. Well-defined nodular densities of various sizes, many of which can be calcified,
may be present. In contrast, more active infiltrates are wider and less well defined, and vessel
margins may be more blurred.
LINEAR AND RETICULAR INTERSTITIAL PATTERNS
PA R A S I T I C P N E U M O N I A
Parasitic pneumonia may be seen with Capillaria aerophila, Filaroides milksi, and
Aelurostrongylus abstrusus infections. 562-567 These are uncommon, but in severe cases they
may produce focal or multifocal alveolar or interstitial pulmonary patterns. Peribronchial
densities may be present throughout the lung, and multifocal nodular densities are seen
(Fig. 2-179). The most obvious changes reportedly involve the caudal lung lobes. Visceral