Page 453 - Atlas of Small Animal CT and MRI

Airways 443

inflammatory response of the airway mucosa. The dis­ Canine eosinophilic bronchopneumopathy
order is more prevalent in small‐breed dogs because CT imaging features of eosinophilic bronchopneumo­
of the association with tracheobronchial collapse and pathy are described in Chapter 4.6. 9
left atrial enlargement, but may be present in dogs of
any breed. Bronchiectasis
CT imaging features are similar to those present on Bronchiectasis is an irreversible dilatation of the bron­
conventional radiographs, with bronchial wall thicken­ chi resulting from chronic airway inflammation that
ing appearing as “doughnuts” when viewed in cross‐ damages elastic components of the bronchi leading to
section and as “tramtracks” when viewed in long axis. bronchial wall destruction and impaired clearance of
Pulmonary parenchyma may also appear diffusely more respiratory secretions. CT features of bronchiectasis in
attenuating than normal because of small airway involve­ people and domestic animals include abnormal bron­
ment. Focal or regional peripheral lung consolidation chial dilation, lack of peripheral bronchial tapering,
may be present in more severe cases. and identification of distinct airways more peripherally
than expected. 10–13 Secondary features of bronchiectasis
Feline bronchial disease include bronchial wall thickening, mucus plugging
Feline eosinophilic pulmonary disease is a complex dis­ within the bronchial lumen, and peripheral air trap­
order that may take on many forms depending on chro­ ping, as reflected by measurable reduced pulmonary
density in affected regions (Figures 4.5.8, 4.5.9, 4.5.10).
nicity and severity. It is thought to be the result of type I
hypersensitivity reaction causing airway inflammatory In people, a bronchoarterial ratio of greater than 1.0 is
an important CT criterion for the diagnosis of bronchi­
response and smooth muscle contraction. With chro­ 10,12
nicity and increasing severity, airway walls become ectasis. However, in dogs the normal upper thresh­
old has been reported to be approximately 2.0, although
thicker, resulting in a typical bronchial pattern. In some 11
patients, inspissated bronchial secretions accumulate bronchiectatic airways can fall below this value.
within airway lumina, resulting in obstruction and Bronchial foreign bodies
characteristic hyperattenuating branching concretions.
In people, the “tree‐in‐bud” sign describes the charac­ The most common bronchial foreign bodies are migrat­
teristic peripheral soft‐tissue attenuating branching ing plant awns, which are prevalent in some parts of the
pattern associated with the accumulation of exudates world. Pulmonary plant awn foreign bodies most com­
in the respiratory bronchioles and alveolar ducts (the monly enter the body through nasal inhalation. They
buds) and the peripheral bronchioles (tree branches). then migrate through the trachea and into the lobar and
8
The subgross anatomy in dogs and cats is somewhat more peripheral bronchi. Multiple awns involving mul­
different from that in people; however, the tree‐in‐bud tiple lung lobes are common. Migrating foreign bodies
pattern is similar. Although airway concretions are eas­ result in multifocal bronchitis that rapidly progresses
ily recognized as being airway oriented and intralumi­ to consolidating focal or lobar pneumonia. Typical CT
nal on CT images, they can sometimes be misdiagnosed features include multifocal mixed alveolar and intersti­
as hyperattenuating pulmonary masses on conventional tial pulmonary infiltrates. The proportion of lung
radiographic images. In the acute phase of feline bron­ involved depends on number and location of plant awns
chial disease, imaging findings may be minimal and and the chronicity of the pneumonia. Although often
limited to reduced airway diameter and increased lung masked by bronchial exudates, the awns can sometimes
volume due to lower airway obstruction. Routine radio­ be detected when surrounded by intraluminal gas
14
graphic imaging would be most commonly employed (Figure 4.5.11).
as part of the diagnostic evaluation at this stage. CT is
employed in patients refractory to treatment or when Neoplasia
radiographic findings are unclear. CT features include Malignant neoplasia originating from the upper airways
evidence of bronchial thickening; diffusely increased is rare, with carcinoma being most common in dogs and
pulmonary density, likely due to terminal airway carcinoma and lymphoma in cats. Rhabdomyosarcomas
involvement; exudative airway collections; and some­ of the canine larynx have also been reported. Chondromas
times hyperinflation due to lower airway obstruction. and osteochondromas may also arise from the tracheal or
This latter feature may be difficult to assess because of bronchial wall. Clinical signs depend on location and
15
assisted ventilation in patients under general anesthesia invasiveness of the neoplasm. Tumors arising from or
(Figures 4.5.5, 4.5.6, 4.5.7). near the larynx may result in voice change, and neoplasms

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