Anatomical and histological comparisons of the epiglottis between brachycephalic, mesocephalic and doliocephalic dogs and puppies

Abstract

In Brachycephalic Obstructive Airway Syndrome (BOAS), anatomical crowding of structures lead to interlinked pathophysiology involving increased negative airway pressure, turbulence and irritation. The syndrome presents with variable functional severity and increased risk of airway maintenance, thermoregulation and anaesthesia. The contribution of head morphology, nares, nasopharynx, tongue, soft palate, palatine tonsils, larynx, trachea and lungs in the pathophysiology of the syndrome has been well characterised. However, the epiglottal component of the larynx of brachycephalic dogs has scant anatomical and histological evaluation for its role in BOAS pathophysiology. In comparison to mesocephalic and doliocephalic dogs, it is hypothesised that the epiglottis of dogs affected by BOAS could have gross morphometric variation (dimension, distortion and relative volume), micromorphometric composition variation (epithelium, lamina propria-submucosa, cartilage core, chondral cell/matrix, fibrous and adipose tissue), and histological variation (inflammation, hyperplasia, reactive and degenerative changes). This study represents the first to demonstrate micromorphometric evaluation of six tissue components using camera-imaging software followed by area calculations from canine epiglottises using a manual approach. Results of this anatomical and histological study showed chondral cell/matrix area and chondral cell numbers were significantly greater in distal, middle or proximal sections of the epiglottis in adult brachycephalic dogs compared to mesocephalic dogs. While not statistically significant, adult brachycephalic dogs had relatively larger epiglottal dimensions compared to similar sized mesocephalic dogs, and brachycephalic individuals displayed subtle tissue proportion, reactive and degenerative differences. Findings suggest that the epiglottis has nuanced structural and histological differences in brachycephalic dogs interlinked with the pathophysiology of BOAS.