Page 322 - Small Animal Internal Medicine, 6th Edition

294 PART II Respiratory System Disorders

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A B C

FIG 20.9
Thoracic radiographs from three different patients, ventrodorsal projections. Radiograph A
shows consolidation of the right middle lung lobe caused by neoplasia. Note that the soft
tissue density of the lung silhouettes with the shadow of the heart. Radiograph B shows
atelectasis of the middle region of the right lung and marked hyperinflation of the
remaining lungs in a cat with idiopathic bronchitis. Note the shift of the heart shadow
toward the collapsed region. Radiograph C shows atelectasis of the right middle lung
lobe in another cat with idiopathic bronchitis. In this patient the adjacent lung lobes have
expanded into the area previously occupied by the right middle lobe, preventing
displacement of the heart.

occurs when an alveolar or interstitial disease process and/or small airway obstruction, as seen in some cats with
progresses to the point at which the entire lobe is filled idiopathic bronchitis; blebs, which are bullae located within
with fluid or cells. Common differential diagnoses for the pleura; and cysts, which are cavitary lesions lined by
lung lobe consolidation are severe bacterial or aspira­ airway epithelium. Parasitic “cysts” (not lined by epithe­
tion pneumonia, neoplasia, lung lobe torsion, and hem­ lium) can form around Paragonimus flukes. Thoracic trauma
orrhage. Inhalation of plant material can also result in is a common cause of cavitary lesions. Other differential
consolidation of the involved lung lobe as a result of the diagnoses include neoplasia, lung infarction (from throm­
inflammatory reaction to foreign material and secondary boembolism), abscess, and granuloma. Cavitary lesions
infection. This differential diagnosis should be consid­ may be apparent as localized accumulations of air or fluid,
ered especially in regions of the country where foxtails are often with a partially visible wall (Fig. 20.10). An air­fluid
prevalent. interface may be visible when standing horizontal beam
projections are used. Bullae and blebs are rarely apparent
Atelectasis radiographically.
Atelectasis is also characterized by a lobe that is entirely Cavitary lesions may be discovered incidentally or on
of soft tissue opacity. In this instance, the lobe is col­ thoracic radiographs of dogs and cats with spontaneous
lapsed as a result of airway obstruction. All the air within pneumothorax. If pneumothorax is present, surgical excision
the lobe has been absorbed and not replaced. It is distin­ of the lesion is usually indicated (see Chapter 24). If inflam­
guished from consolidation by the small size of the lobe matory or neoplastic disease is suspected, further diagnos­
(see Fig. 20.9, B). Often the heart is displaced toward the tic testing is indicated. If the lesion is found incidentally,
atelectatic lobe. Atelectasis is most commonly seen involv­ animals can be periodically reevaluated radiographically to
ing the right middle lobe of cats with bronchitis (see Fig. determine whether the lesion is progressing or resolving.
20.9, C). Displacement of the heart may not occur in If the lesion does not resolve during the course of 1 to 3
these cats. months, surgical removal is considered for diagnostic pur­
poses and to prevent potentially life­threatening spontane­
Cavitary Lesions ous pneumothorax.
Cavity lesions describe any abnormal air accumulation in
the lung. They can be congenital, acquired, or idiopathic. Lung Lobe Torsion
Specific types of cavitary lesions include bullae, which result Lung lobe torsion can develop spontaneously, particularly in
from ruptured alveoli due to congenital weakness of tissues deep­chested dogs, or as a complication of pleural effusion