Brachycephalic Obstructive Airway Syndrome (BOAS)

What makes up BOAS? The most common components of this disease are both stenotic nares(nostril) and an elongated soft palate. These two features are commonly seen. Other components are everted saccules, hypoplastic trachea, and secondary laryngeal collapse. In dogs that have stenotic nares the cartilage that makes up the nares is generally thicker and more condensed and oftentimes more medially displaced which causes an obstruction. Also, the conchae(cartilage in the nasal passageway) can be altered and displaced causing further airway turbulence and obstruction.

Anatomically the soft palate is just caudal(behind) to the hard palate and further divides the nasopharynx from the oropharynx (nasal passage from the mouth or oral cavity). In the normal patient the soft palate will typically extend caudally to just touch (slightly overlap) the epiglottis. In patients with an active obstruction this can be seen to extend 1-2 cm (or more) past the epiglottis. Due to this extension past the epiglottis, this tissue can actively obstruct airflow into the larynx and also become edematous(swollen) and undergo inflammation. Inflammation from this airway obstruction can extend to the tissue surround the pharyngeal region.

Generally considered to be a secondary side effect of the aforementioned conditions, everted saccules can develop due to the presence of increased air pressure of a prolonged period of time. Laryngeal saccules are normal out-pouchings noted adjacent to the vocal folds. Normally they extend outward away from the airway. After being under constant negative pressure these out-pouchings will evert and extend into the caudal laryngeal lumen causing an obstruction. Another secondary effect noted due to the constant high pressure is laryngeal collapse. This generally occurs in later stages of the disease process and will progress in severity. There is a grading scale that is used to assess the condition. Grade I laryngeal collapse is present when the laryngeal lumen is narrowed by everted saccules. Grade II collapse is characterized by both everted saccules and the cuneiform processes begin to collapse inward and fail to abduct during inspiration. Grade III collapse is characterized by the addition of the corniculate processes inwardly folding during inspiration, which signifies complete collapse.

The next posting will go over some of the physical exam findings and what we can do to help these patients out for the long run.

Note the narrow nostrils.

Note the narrow nostrils.

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