Radiographic tracheal and carina distension is associated with diagnosis of laryngeal paralysis in dogs.

Objective: To determine whether radiographic carina distension is a potential diagnostic indicator of laryngeal paralysis (LP) in dogs.

Methods: Dogs diagnosed with LP on upper airway examination at a veterinary specialty hospital were retrospectively identified if they underwent orthogonal thoracic radiographic evaluation between January 2013 and January 2024. Each case was matched 1:1 with similar patients without underlying cardiorespiratory disease that underwent orthogonal thoracic radiographic evaluation. The thoracic inlet (TI), intrathoracic (TT), and carina tracheal diameters (CD) as well as the width of the proximal third rib (3R) were measured with picture archiving and communication system software for each lateral projection of preoperative radiographs. The TT:TI, TT:3R, TI:CD, TT:CD, CD:3R, and TI:3R ratios were calculated.

Results: Mean (SD) CD:3R, TT:3R, and TI:3R ratios were significantly higher in dogs with LP. The mean (SD) ratio for LP dogs and non-LP control dogs was 3.16 (0.61) and 1.94 (0.21) for CD:3R, 2.81 (0.56) and 1.71 (0.21) for TT:3R, and 2.55 (0.52) and 1.55 (0.20) for TI:3R. For every 0.10 increase in the ratio, the odds of a dog having LP increased by 1.87 times for CD:3R (95% CI, 1.54 to 2.4), 2.1 times for TT:3R (95% CI, 1.68 to 2.8), and 2.2 times for TI:3R (95% CI, 1.74 to 3.1). The area under the receiver operator characteristics curve was 0.97 (95% CI, 0.95 to 1.00), 0.98 (95% CI, 0.96 to 1.00), and 0.98 (95% CI, 0.95 to 1.00) for CD:3R, TT:3R, and TI:3R, respectively, indicating outstanding diagnostic discrimination.

Conclusions: Tracheal diameter ratios of 2.3 (CD:3R), 1.9 (TT:3R), and 1.9 (TI:3R) or greater were associated with LP in dogs.

Clinical relevance: Tracheal and carina diameter ratios may help guide ancillary diagnostic testing in cases of suspected LP.