CT Reveals Why BOAS Severity Differs by Breed: Distinct Airway Risk Profiles in Pugs, French Bulldogs, and Bulldogs

Breed-specific anatomical risk factors of brachycephalic obstructive airway syndrome: A comprehensive computed tomographic study from nares to cervical trachea

Nai-Chieh Liu; Eileen L. Troconis; David R. Sargan; Jane F. Ladlow

Background

Brachycephalic obstructive airway syndrome (BOAS) shows wide variation in severity among dogs with similar external conformation. Previous studies have described upper airway lesions using advanced imaging, but breed-specific anatomical contributors to BOAS severity remain unclear. This study aimed to identify computed tomographic (CT)–defined upper airway lesions associated with BOAS severity in pugs, French bulldogs, and bulldogs, using the BOAS index derived from whole-body barometric plethysmography as an objective measure of airway obstruction.

Methods

This prospective cross-sectional study included 113 client-owned dogs (40 pugs, 52 French bulldogs, and 21 bulldogs). All dogs underwent respiratory function testing to obtain a baseline BOAS index and CT imaging of the head and neck from nares to cervical trachea. Eleven validated CT-derived anatomical measurements and laryngeal collapse grading were recorded. Breed-specific univariate and multivariate linear regression models were used to assess independent associations between anatomical variables and BOAS index.

Results

Distinct breed-specific anatomical risk factors were identified. In pugs, increased soft tissue proportion at the rostral nasopharyngeal meatus and Grade III laryngeal collapse were significantly associated with higher BOAS index. In French bulldogs, a smaller nasopharyngeal index and the presence of Grade I or Grade II laryngeal collapse were associated with increased BOAS severity. In bulldogs, a smaller tracheal perimeter, smaller nasopharyngeal index, and higher skull index were independently associated with higher BOAS index. The contributory lesions differed markedly among breeds, and multivariate models explained 41.3%, 56.0%, and 63.8% of BOAS index variance in pugs, French bulldogs, and bulldogs, respectively.

Limitations

The study relied on static CT imaging acquired under general anesthesia, which may not fully reflect dynamic airway collapse during respiration. Certain airway regions were excluded from measurement due to interference from endotracheal tube placement. Additionally, CT cannot accurately assess nasal mucosa, potentially underestimating some intranasal obstructions.

Conclusions

BOAS severity is associated with different anatomical risk factors in pugs, French bulldogs, and bulldogs. Some contributory lesions, such as hypoplastic trachea in bulldogs, are not amenable to surgical correction and should be targeted through selective breeding. The findings support the use of CT for breed-specific surgical planning, prognostication, and informed breeding strategies, emphasizing that BOAS is a multi-lesional and breed-dependent condition.

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