Page 452 - Atlas of Small Animal CT and MRI

4.5

Airways

Normal airways Tracheal and bronchial developmental

The large airways are well delineated on CT images disorders
since the soft‐tissue attenuating airway walls are defined A single CT report describes tracheal hypoplasia in two
both internally and externally by a gas‐attenuating English Bulldog puppies but does not include quantitative
interface. CT quantification of tracheal diameter has data. Computed tomography features of other tracheal
5
been performed in anesthetized German Shepherd and bronchial dysplasia have not been previously reported
Dogs and revealed a consistent horizontal to vertical in the dog or cat. Common imaging features in people
ratio of approximately 1.0, with luminal cross‐sectional include bronchi originating from an abnormal location
area progressively decreasing from the cranial cervical and segmental or complete atresia or hypoplasia with
region to the thoracic cavity. A CT evaluation of the resulting narrowing of the airway lumen (Figure 4.5.2). 6
1
trachea in normal dogs during respiration revealed a
decrease in tracheal cross‐sectional area during inspira­ Trauma
tion, with the change in area being primarily attributa­ Tracheal trauma with mural disruption can result in res­
ble to a decrease in vertical tracheal diameter. Many of piratory compromise as well as pneumomediastinum,
these dogs had invagination of the dorsal tracheal mem­ subcutaneous emphysema, and pneumothorax. CT fea­
brane at expiration. Ratios of lobar bronchi diameters tures include discontinuity of the tracheal wall and a
2
to corresponding pulmonary arterial diameters in nor­ variable volume of extraluminal gas (Figure 4.5.3).
mal dogs have been reported to average 1.45 with an Iatrogenic pulmonary barotrauma from positive‐
3
upper limit of 2.0 (Figure 4.5.1). Bronchial/arterial pressure ventilation of anesthetized patients can occa­
ratio measurements obtained in anesthetized normal sionally lead to alveolar or small airway rupture in
cats yielded a mean value of 0.71 with an estimated people, with resulting perivascular gas dissection. We
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upper limit of 0.91. 4 have seen a similar phenomenon in dogs, which appears
CT is not routinely used to evaluate dynamic as a thin gas‐attenuating layer surrounding pulmonary
changes of the major airways since patients are often blood vessels on CT images (Figure 4.5.4).
intubated, anesthetized, and mechanically ventilated.
However, one report describes dynamic tracheal and Inflammatory disorders
bronchial collapse due to airway wall malacia on CT
images in sedated and nonintubated dogs. Bronchial Tracheobronchitis
collapse was defined as a width to height ratio of Chronic bronchitis is common in dogs and is typically
greater than 2. 5 associated with an underlying neutrophilic/eosinophilic

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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