Missing the Mark: When X-rays Underestimate a Dog’s Collapsing Trachea

Radiography underestimates the severity of tracheobronchoscopy-confirmed grade IV tracheal collapse in dogs

Masahiro Suematsu, Caroline V. Fulkerson, Reo Nishi, Masahiro Murakami

Background
Tracheal collapse (TC) is a prevalent respiratory disorder in small-breed dogs, typically evaluated using radiography or tracheobronchoscopy. While tracheobronchoscopy is the gold standard for diagnosis, radiography is more accessible but known to underestimate the disease's severity. This study aims to quantify the agreement between radiographic and tracheobronchoscopic findings in grade IV TC and to assess the prevalence of a specific radiographic pattern termed tracheal collapse with axial rotation (Rad-AR), which has previously been underreported.

Methods
A retrospective analysis was performed on 78 dogs diagnosed with grade IV TC via tracheobronchoscopy between 2021 and 2024. Radiographic evaluations (inspiratory and expiratory right-lateral thoracic views) and tracheobronchoscopic assessments were conducted independently by experts. Four tracheal regions were evaluated: midcervical, thoracic inlet, midthoracic, and carina. Tracheal collapse was classified as mild (≤50%) or severe (>50%) based on the most pronounced radiographic finding. Statistical comparisons included weighted kappa statistics and percentage agreements.

Results
Severe TC was consistently detected at the thoracic inlet (100%) via tracheobronchoscopy, but radiography showed severe collapse in only 87.2% of these cases. Radiographic detection of severe collapse at other sites was lower: 48.7% at midcervical, 11.5% at midthoracic, and 11.5% at the carina. Agreement between modalities was fair only at the midthoracic site (weighted κ = 0.24) and slight to poor elsewhere. Notably, 11 dogs showed no radiographic evidence of collapse despite confirmed grade IV TC. The Rad-AR pattern was seen in 21.8% of cases at the thoracic inlet.

Limitations
The retrospective nature and focus solely on grade IV cases may limit generalizability. Absence of a direct comparison with fluoroscopy and the inability to confirm Rad-AR anatomically are additional limitations. Potential effects of anesthetic agents during tracheobronchoscopy were acknowledged, though minimized.

Conclusions
Radiography, while useful for screening severe TC at the thoracic inlet, fails to detect or underestimates disease in many cases, particularly in midcervical, midthoracic, and carinal regions. Tracheobronchoscopy remains essential for accurate diagnosis and treatment planning. The Rad-AR pattern is not rare and should be recognized to avoid misinterpretation. A multimodal diagnostic approach is recommended to improve detection and clinical decision-making in canine TC.

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