CT and radiographic evaluation of bronchial collapsibility at forced expiration in asymptomatic brachycephalic dogs

A retrospective study of tracheal collapse in small-breed dogs: 110 cases (2022-2024)

Background

The grade of tracheal collapse (TC) is assessed by the diameter of the narrowed lumen. However, studies on the relationship between TC grade and clinical symptom severity are lacking.

Objectives

To investigate the clinical characteristics of small-breed dogs diagnosed with TC and determine if fluoroscopic grading correlates with cough severity.

Methods

We retrospectively reviewed medical records from 2022 to 2024. TC diagnosis was confirmed using fluoroscopic examination. Multiple linear regression was employed to investigate factors influencing cough severity, with a significance level set at p < 0.05.

Results

A total of 132 dogs with TC were identified, of which 22 were excluded. The final cohort consisted of 110 dogs, aged between 2-19 years, with no significant sex differences. The majority (97.2%) of dogs had a BCS of ≥4. Among the top four breeds (Maltese, Pomeranian, Poodle, and Chihuahua), the most severe collapse was observed in the carinal region. The grade of collapse on fluoroscopy was mostly related to high BCS (p < 0.007) and low body weight (p < 0.001). However, interestingly, fluoroscopic findings of collapse location and grade did not correlate with cough severity (p = 0.350). Notably, clinical symptoms improved in 86.6% of cases following interventions such as weight reduction, environmental changes, and pharmacotherapy.

Conclusions and clinical relevance

In small-breed dogs, the severity of cough was not associated with the region or grade of TC diagnosed by fluoroscopy.

Fluoroscopically measured bronchial collapse in healthy dogs during cough exceeds 25%, and a cutoff of 60% bronchial collapse can be used to distinguish healthy from chronically coughing dogs

Bronchomalacia, the weakening of bronchial cartilage, is a common cause of cough in dogs. The gold standard for diagnosis of bronchomalacia is bronchoscopy; however, fluoroscopy is often used as a preliminary diagnostic test due to its noninvasiveness. The normal amount of bronchial collapse in healthy dogs using fluoroscopy has not been previously established, with some authors citing <25%. The aims of this prospective and retrospective analytical observational study were to determine the normal amount of airway collapse in healthy animals, the amount of airway collapse in dogs with chronic cough and presumed bronchomalacia, and cut-off values of airway collapse during expiration and cough to distinguish between the two groups. Thoracic fluoroscopy was performed in right and left lateral recumbency during inspiration, expiration, and cough to evaluate the percentage collapse of the trachea and lobar bronchi in 45 healthy and 76 chronically coughing dogs. The bronchi of chronically coughing dogs exhibited a significantly greater amount of collapse during both expiration and cough compared with healthy dogs. Chronically coughing dogs exhibited up to 31.7 ± 26.6% collapse in expiration and 87.5 ± 23.7% collapse during cough, whereas healthy dogs exhibited 14.9 ± 6.1% collapse in expiration and 35.0 ± 13.7% collapse during cough. Based on ROC curves, the authors suggest using cut-off values of 30% during expiration and 60% during cough to distinguish between healthy dogs and those with presumed bronchomalacia. Findings suggest that though healthy dogs can exhibit a greater degree of airway collapse than previously thought, fluoroscopy can be used to distinguish between healthy and presumed bronchomalacic dogs.

Computer tomography measurements of the airway and thoracic cavity do not provide support for bronchial conformation as a predisposing factor of left cranial lung lobe torsion in pugs

The objective of this retrospective clinical study was to determine if airway or thoracic cavity measurements in pugs, particularly the left cranial lung lobe, were significantly different from brachycephalic and mesocephalic control. Thoracic computed tomographic studies of 10 pugs, French bulldogs (FB), and Jack Russell Terriers (JRT) were analyzed. Thoracic height: width ratio (H:W), cross-sectional areas of the left mainstem bronchus (CSA LMB), left cranial lung lobe bronchus (CSA LCrBr), left caudal lung lobe bronchus (CSA LCauBr), CSA LCrBr relative to length (CSA LCrBr/length) and CSA LCauBr/length were measured and adjusted to body weight (/kg). CSA LMB/kg, CSA LCauBr/length/kg, and CSA LCrBr/length /kg were smaller in pugs and FB compared with JRT (P < .05), but no differences were found between pugs and FB. Cross-sectional areas of left cranial lung lobe bronchus /kg and CSA LCauBr/kg were smaller in pugs than JRT (P < .05), but no differences were found between pugs and FB or FB and JRT. No difference was found in thoracic H:W between any breeds. This demonstrated that pugs and FB had significantly narrower bronchi CSA/lengths ratios compared with JRT, but this was not limited to the LCBr. Airway measurements were not significantly different between brachycephalic breeds; therefore, the pugs' predisposition to left cranial lung lobe torsion cannot be solely explained by narrower lower airways.

Prevalence of bronchial wall thickening and collapse in brachycephalic dogs with and without brachycephalic obstructive airway syndrome and in nonbrachycephalic dogs

OBJECTIVE

To assess the prevalence of bronchial wall thickening (BWT) and collapse in brachycephalic dogs with and without brachycephalic obstructive airway syndrome (BOAS) and in nonbrachycephalic dogs.

ANIMALS

85 dogs with no history of lower respiratory tract disease that underwent CT of the thorax.

PROCEDURES

Electronical medical records for March 2011 through August 2019 were reviewed to identify brachycephalic dogs with BOAS (BOAS group) and brachycephalic dogs without BOAS (BDWB group) that did not have any evidence of lower respiratory tract disease and had undergone thoracic CT. A population of nonbrachycephalic dogs of similar weight (control dogs) was also retrospectively recruited.

RESULTS

BWT was identified in 28 of 30 (93.3%; 95% CI, 80.3% to 98.6%) dogs in the BOAS group, 15 of 26 (57.7%; 95% CI, 38.7% to 75.0%) dogs in the BDWB group, and 10 of 28 (35.7%; 95% CI, 20.1% to 54.2%) control dogs. On multivariable analysis, only brachycephalic conformation (P < 0.01) and body weight (P = 0.02) were significantly associated with the presence of BWT. Bronchial collapse was identified in 17 of 30 (56.7%; 95% CI, 39.0% to 73.1%) dogs in the BOAS group, 17 of 26 (65.4%; 95% CI, 46.3% to 81.3%) dogs in the BDWB group, and 3 of 28 (10.7%; 95% CI, 3.1% to 25.9%) control dogs. On multivariable analysis, only brachycephalic conformation was significantly (P < 0.01) associated with the presence of bronchial collapse.

CLINICAL RELEVANCE

A relationship between brachycephalic conformation and body weight with BWT was established, with heavier dogs having thicker bronchial walls. However, further studies are required to investigate the cause. Bronchial collapse was also more common in dogs with brachycephalic conformation, which is in agreement with the previously published literature.

Clinicopathologic features, comorbid diseases, and prevalence of pulmonary hypertension in dogs with bronchomalacia

Background

Reports of clinicopathologic features of bronchomalacia (BM) differ because of inconsistent definitions and frequent prevalence of comorbid cardiopulmonary disease. Pulmonary hypertension (PH) secondary to BM is poorly described.

Objectives

Dogs with BM will be older but of any somatotype, and increased expiratory effort, ≥1 comorbid disease, and PH will be more common than in dogs without BM.

Animals

Client‐owned dogs (n = 210) evaluated for respiratory signs.

Methods

Medical records of dogs with paired inspiratory: expiratory‐breath‐hold computed tomography, tracheobronchoscopy, or both between January 2016 and December 2019 were retrospectively reviewed. Comparisons between dogs with and without BM using Mann‐Whitney rank sum or χ² tests (P < .05 significant were made). Because of high numbers of variables, criteria with high prevalence (>25%) were identified (n = 10) for univariate analysis (P < .005 significant). Significant variables were submitted for multivariate analysis.

Results

Bronchomalacia was identified in 41% of dogs of all sizes/somatotypes; 38% were >10 kg. All dogs with BM had ≥1 comorbid cardiopulmonary disorder. Dogs with BM were significantly older (P < .001), smaller (P < .001), and were more likely diagnosed with tracheal or mainstem bronchial collapse (P < .001) or bronchiectasis (P < .001). Multivariate analysis confirmed associations with age, tracheal or mainstem bronchial collapse, and bronchiectasis. In dogs with BM, PH was more prevalent.

Conclusions and Clinical Importance

Although significantly more common in older, smaller dogs, BM occurs in dogs of all sizes and in all instances with comorbidities. Echocardiography should be considered in dogs with BM to identify PH.