Abstract
BackgroundTracheal narrowing due to congenital tracheal hypoplasia, acquired tracheal stenosis and tracheal collapse can lead to life-threatening respiratory distress. Tracheal hypoplasia has been identified in brachycephalic dog breeds, predominantly English Bulldogs, by measuring the tracheal diameter compared to the diameter of the thoracic inlet and creating a ratio. However, reference ranges for tracheal diameter have not been established for non-brachycephalic small breed dogs. It would be advantageous to have established tracheal diameters for non-brachycephalic small breed dogs, as these are the dogs most at risk of tracheal collapse. The main objective, of this study was to radiographically evaluate vertical tracheal diameter (VTD) at three standardized locations along the trachea of non-brachycephalic small breed dogs, in an attempt to further establish a screening diagnostic protocol for canine tracheal hypoplasia. Medical records and thoracic radiographs of non-brachycephalic small breed dogs without respiratory disease were reviewed. Right lateral radiographs were reviewed. The absolute and average VTDs at three locations (location A: caudal cervical VTD; location B thoracic inlet VTD; location C: intrathoracic VTD) were standardized by manubrium length (ML), as well as by the previously utilized thoracic inlet distance (Ti-D) and proximal 3rd rib width (PR3-W) to calculate manubrium-tracheal index (M-TI), thoracic inlet-tracheal index (Ti-TI), and proximal R3-tracheal score (PR3-TS), respectively. Correlations between averaged tracheal diameter and each of the ML, Ti-D, and PR3-W, and between M-TI and each of Ti-TI and PR3-TS were calculated.ResultsEighty-one healthy dogs met the criteria for inclusion. Significant differences (P < 0.0001) were identified among the mean values of the absolute and standardized VTDs at levels A, B, and C. The smallest tracheal diameter was identified at the level of the thoracic inlet (Level B).The average VTD correlated better with ML (rs = 0.82, P < 0.0001) compared to Ti-D and PR3-W. A relatively strong correlation (rs = 0.77, P < 0.0001) was identified between the averaged manubrium tracheal index (M-TI) and thoracic inlet tracheal index (Ti-TI).ConclusionM-TI is an appropriate alternative to Ti-TI and PR3-TS to radiographically evaluate VTD in dogs. M-TI < 0.43, < 0.34, or < 0.38 at level A, B, or C, respectively, may indicate tracheal hypoplasia in non-brachycephalic small breed dogs. Screening of canine VTD could be achieved using M-TI.
Highlights
Tracheal narrowing due to congenital tracheal hypoplasia, acquired tracheal stenosis and tracheal collapse can lead to life-threatening respiratory distress
Our 2nd hypothesis is that manubrium tracheal index (M-TI) could be an appropriate alternative to thoracic inlet-tracheal index (Ti-TI) and proximal R3-tracheal score (PR3-TS) in the radiographic assessment of canine tracheal index
Vertical tracheal diameter (VTD) measured at thoracic inlet region was 20.9 and 10.9% narrower than vertical tracheal diameter (VTD) measured at caudal cervical and intrathoracic regions, respectively; 3) the average VTD correlated better with the manubrium length compared to thoracic inlet distance and proximal 3rd rib width; 4) manubrium tracheal index (M-TI) correlated better with thoracic inlet tracheal index (TiTI, rs = 0.77) compared to proximal 3rd rib tracheal score (PR3-TS, rs = 0.63); 5) means M-TI at levels A, B, and C were 0.45, 0.35, and 0.39, with concomitant 95% CIs being 0.43–0.46, 0.34–0.36, and 0.38–0.40, respectively
Summary
Tracheal narrowing due to congenital tracheal hypoplasia, acquired tracheal stenosis and tracheal collapse can lead to life-threatening respiratory distress. The main objective, of this study was to radiographically evaluate vertical tracheal diameter (VTD) at three standardized locations along the trachea of non-brachycephalic small breed dogs, in an attempt to further establish a screening diagnostic protocol for canine tracheal hypoplasia. Medical records and thoracic radiographs of non-brachycephalic small breed dogs without respiratory disease were reviewed. Fluoroscopy and bronchoscopy were established to diagnose and monitor dynamic tracheal collapse in dogs [8, 11]. Among these diagnostic procedures, radiography has been found to be the most widely used modality among practitioners [12, 13]. The commonly utilized radiographic procedures included measurement of the VTD at the thoracic inlet to be standardized by the thoracic inlet distance (Ti-D) [2, 6, 7, 14, 15] or the proximal 3rd rib width (PR3-W) [7, 15, 16]
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