Anatomical evaluation of soft palate in adult and neonate brachycephalic dogs: morphological features at the basis of brachycephalic airway obstructive syndrome

Introduction: Increased length of soft palate is one of the main factors contributing to pharyngeal narrowing during respiratory activity in brachycephalic dogs. However, no histological studies assessing soft palate morphology and normal tissue composition in brachycephalic breeds are available. The aim of this study was to compare soft palate morphology in brachycephalic versus mesocephalic dogs in order to identify potential anatomical differences involved in the pathogenesis of the brachycephalic airway obstructive syndrome (BAOS), a disease which very frequently affects these breeds during their postnatal life. The soft palate of brachycephalic neonates was also examined to evaluate its morphology at birth. Methods: Specimens from brachycephalic dogs (N=11) with long soft palate and from mesocephalic dogs (N=8) were collected at surgery and euthanasia respectively, processed for histology and examined at six transversal levels. The soft palate dissected from brachycephalic neonates (N=10) dying spontaneously at birth of unrelated conditions was examined as well. Results: Compared with mesocephalic soft palates, brachycephalic samples showed progressive, quali-quantitative changes, such as thickened superficial epithelium, extensive increase of interfibrillar matrix, oedema of the lamina propria and mucous gland hyperplasia. Muscular degenerative changes were evidenced. In the soft palate of neonate brachycephalic dogs lesions were absent. Conclusions: The results of this investigation add further insights into the anatomy of soft palate in the canine species and identify key morphological features at the basis of soft palate thickening in brachycephalic dogs. Functional impairment of soft palate associated with BAOS is morphologically justified by oedema, increased intercellular myxoid matrix as well as increased mucin production by the hyperplastic glands. Based on these findings, a likely hypothesis is that the dysfunctional inspiratory efforts induce chronic vibration and microtrauma that cause the soft palate changes identified in brachycephalic dogs. This hypothesis is further substantiated by absence of tissue lesions in newborn brachycephalic dogs.