There are several reports in the veterinary literature on tracheal assessment; however, there is a lack of studies on the trachea in voluntarily breathing dogs. The aim of this study was to describe the natural shape of the trachea in awake dogs and to assess tracheal dimensions and the width-to-height ratio. Thoracic computed tomographic images of awake small breed dogs without any signs of respiratory malfunction (n = 19) were evaluated. Each trachea was categorised into one of four different shapes: circular, horseshoe, crescent or focal dorsal invagination. The circular shape was prominent, particularly in the thoracic inlet and intrathoracic area, while the horseshoe shape was also normally present. In this group of normal dogs, there were no crescent-shaped tracheas, but focally invaginated tracheas were observed. The mean tracheal heights at five locations, namely the caudal endplate of the fourth cervical vertebra, cranial endplate of the seventh cervical vertebra, mid-body of the first thoracic vertebra, mid-body of the third thoracic vertebra, and 1 cm cranial to the carina were 9.12, 8.96, 9.34, 9.88 and 10.16 mm, respectively. The widths at these same sites were 12.26, 10.42, 10.07, 9.82 and 10.23 mm, respectively. The width-to-height ratios of each tracheal location were 1.38, 1.20, 1.10, 1.01 and 1.03, the last two of which are consistent with the circular shape of the intrathoracic trachea. Multi-detector computed tomography under non-general anaesthesia is a non-invasive and unparalleled imaging tool for describing tracheal appearance in healthy awake dogs.
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