Can a Chest Radiograph Reveal Laryngeal Paralysis? New Evidence Points to the Carina

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

Rachel E. Natsume, DVM; Mariana T. Quina, DVM, DACVS; Jason B. Arble, DVM, DACVR; Steven W. Frederick, LVT, VTS; Lauren E. Drenning

Background

Laryngeal paralysis (LP) in dogs results from failure of arytenoid cartilage abduction, leading to upper airway obstruction. Definitive diagnosis requires laryngeal examination under sedation or anesthesia, which may be impractical or risky in some clinical settings. Thoracic radiographs are routinely obtained as ancillary tests, and anecdotal observations suggest that dogs with LP may exhibit distension of the tracheal carina. This study investigated whether radiographic tracheal and carina diameter ratios are associated with LP and could serve as a noninvasive screening indicator.

Methods

A retrospective, case-matched study was conducted at a single veterinary specialty hospital. Dogs with confirmed LP that underwent preoperative 3-view thoracic radiography between January 2013 and January 2024 were identified and matched 1:1 with dogs of similar age, weight, and breed without known cardiorespiratory disease. Tracheal diameters at the thoracic inlet (TI), intrathoracic trachea (TT), and carina (CD), along with the width of the proximal third rib (3R), were measured on lateral radiographs. Multiple tracheal diameter ratios were calculated and analyzed using logistic regression and receiver operating characteristic (ROC) curve analysis to assess diagnostic performance.

Results

Dogs with LP had significantly higher CD:3R, TT:3R, and TI:3R ratios compared with control dogs. For every 0.10 increase in these ratios, the odds of having LP increased between 1.87- and 2.2-fold. All three ratios demonstrated outstanding diagnostic discrimination, with areas under the ROC curve ranging from 0.97 to 0.98. Optimal cutoff values associated with LP were ≥ 2.3 for CD:3R, ≥ 1.9 for TT:3R, and ≥ 1.9 for TI:3R, each providing high sensitivity and specificity. Measurement reliability was excellent when triplicate measurements were averaged.

Limitations

The study’s retrospective design resulted in nonstandardized radiographic technique and variable respiratory phase at image acquisition. Measurements were performed by a single, nonblinded observer, and dogs in the control group did not undergo laryngeal examination, raising the possibility of undetected subclinical LP. Additionally, results were derived from a referral population with overrepresentation of certain breeds, particularly Labrador Retrievers.

Conclusions

Radiographic distension of the trachea and carina, expressed as specific tracheal diameter ratios, is strongly associated with a confirmed diagnosis of laryngeal paralysis in dogs. While not a replacement for laryngeal examination, these ratios may serve as a useful, noninvasive screening tool to guide further diagnostic decision-making. Prospective studies are warranted to validate these findings and define their role in clinical practice.

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