Page 469 - Atlas of Small Animal CT and MRI

Small Airways and Parenchyma 459

Developmental disorders many underlying causes: neurogenic causes; pulmonary
embolic disorders; and occasionally an adverse response
Emphysema to drugs or toxins. CT features of noncardiogenic edema
There is a small number of reports of dogs with emphy- include mixed interstitial to alveolar infiltrates with a
sema that is associated with underlying bronchial random multifocal or coalescing distribution (Figure
hypoplasia and bronchiectasis. A proposed mecha- 4.6.5). In patients with ARDS, the severity of pulmonary
2–5
nism is dynamic expiratory bronchial collapse leading infiltrates may be profound, and the imaging appearance
to increased intrapulmonary pressure and subsequent may be altered by superimposition of underlying inflam-
3
development of emphysema. Imaging reports are spo- matory lung disease.
radic but include pulmonary hyperlucency, regional
lobar collapse, and pneumothorax (Figure 4.6.2). Pulmonary contusion and hemorrhage
Pulmonary bulla Pulmonary contusion from trauma and overt pulmo-
Pulmonary bullae are often developmental and may have nary hemorrhage due to trauma, bleeding diatheses, or
a similar underlying pathophysiologic mechanism as other underlying lung pathology varies in appearance
described above for emphysema. Bullae are generally clin- depending on the initiating cause and severity. CT fea-
ically silent unless less they rupture leading to pneumo- tures consist of regional interstitial to alveolar infiltrates
thorax. Pulmonary bullae can also result from shearing that are typically asymmetrical and may be unilateral
6,7
trauma of lung parenchyma, arise as a sequela to underly- (Figure 4.6.6). Fulminant bleeding may flood airways
ing pulmonary parenchymal disease, or be idiopathic. and alveoli, mimicking lobar consolidation from other
Bullae are thin‐walled, well demarcated, and hypoat- causes. In trauma patients, the CT diagnosis of pulmo-
tenuating to adjacent normal pulmonary parenchyma nary contusion is sometimes confounded by the pres-
on CT images (Figure 4.6.3). Clinically silent bullae are ence of positional atelectasis that results in increased
easily detected on routine CT imaging but are often pulmonary attenuation from volume loss.
obscured in the presence of pneumothorax. The clinical
value of CT for bulla detection is reported to be low in Lung lobe torsion
dogs with spontaneous pneumothorax. Detection rate Lung lobe torsion has been reported in both dogs and cats,
improves with increasing bulla size but does not seem to and Pugs are predisposed to the disorder. 9–11 Lobar torsion
correlate with the severity of pneumothorax. 8 is frequently a sequela of chronic pleural effusion, with the
left cranial and right middle lobes most often involved and
Pulmonary edema rarely more than one lung lobe. CT features include pleu-
ral effusion and abrupt termination of the affected lung
Cardiogenic edema lobe bronchus. Additional findings are lobar enlargement,
Cardiogenic edema due to left ventricular failure results peripheral parenchymal collapse/consolidation, and cen-
from increased intravascular hydrostatic pressure at the tral vesicular emphysema (Figures 4.6.7, 4.6.8). 10,11
level of the pulmonary capillaries, causing extravasation Emphysematous lobes have mild or absent enhancement
of transudative edema fluid into adjacent lung interstit- following intravenous contrast administration because of
ium. CT features of cardiogenic pulmonary edema torsional vascular occlusion and necrosis. Lung lobes that
include interstitial to alveolar infiltrates that may be mul- have undergone torsion and are small in size are less
tifocal or coalescing. Mild to moderate infiltrates have a affected by necrosis, possibly due to hyperacute or chronic
ground‐glass appearance, representing interstitial and time course or partial torsion. These atelectatic lobes are
partial alveolar edema (Figure 4.6.4). Left atrial and ven- contrast enhancing as they retain blood supply. Virtual CT
tricular enlargement can also be seen, and pulmonary bronchoscopy has also been reported to aid in diagnosis.
10
venous enlargement, though often present, is inconsist- Partial lobar torsion can occasionally occur and is more
ent. Cardiogenic edema typically has a perihilar distribu- challenging to diagnose since characteristic features asso-
tion in dogs but no characteristic distribution in cats. ciated with complete torsion may be absent.

Noncardiogenic edema Inflammatory lung disorders
Noncardiogenic pulmonary edema is caused by increased
pulmonary capillary permeability, resulting in extravasa- Idiopathic interstitial pneumonia
tion of high‐protein fluid into the interstitial space. The A number of inflammatory interstitial lung disorders
most common initiators of noncardiogenic edema are in people fall under the broad category of idiopathic
acute respiratory distress syndrome (ARDS), which has interstitial pneumonia. Although the array of speculated
12
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