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Cornell Richard P. Riney Canine Health Center

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Brachycephalic Obstructive Airway Syndrome (BOAS)

This condition is also known by other names including: brachycephalic syndrome, brachycephalic airway syndrome, brachycephalic respiratory syndrome, or congenital obstructive upper airway disease.

A 2-year old Boston Terrier named Lou.

What is meant by a brachycephalic dog?

This is a scientific term describing a dog that has a shortened muzzle (or nose) due to its genetics (breed).  The skull bones of these dogs are compressed such that the dog has a more flattened or “pushed-in” facial conformation compared to other dogs.  

What breeds of dogs are considered brachycephalic?

This condition is seen most frequently in the English bulldog, pug, French bulldog, and Boston terrier (pictured left). Other affected breeds include the boxer, Pekingese, shih tzu, Chinese sharpei, Lhasa apso, and bull mastiff. 

What problems are associated with this condition?

The anatomical variations of the skull bones result in abnormalities of the upper respiratory system. Overall, there can be varying degrees of breathing difficulty depending on the extent of the abnormalities. The severity of symptoms may increase as the dog ages. 

What causes BOAS?

There are several possible respiratory tract variations and some or all of them can be found in an individual dog.  All of them contribute to the obstruction of airflow. 

The major findings include:

  • Stenotic nares are congenitally small nostrils that may also collapse as the dog inhales
  • An elongated soft palate can cause obstruction of airflow into the larynx
  • Everted laryngeal saccules refers to tissue near the vocal cords that is pulled inward during inhalation and can block airflow
  • Some dogs may have a windpipe that is proportionally too narrow and is referred to as a hypoplastic trachea

Other possible findings that can contribute to airflow obstruction include:

  • Laryngeal collapse 
  • Large tongue
  • Enlarged or everted tonsils
  • Nasopharyngeal turbinates

Over time the condition worsens as a result of the dog working harder to breathe. Tissues in the throat can become swollen or inflamed, further obstructing the flow of air. 

How is BOAS diagnosed?

Most dogs are diagnosed between one and four years of age.  Males and females are affected equally. 

The diagnosis is made based on a combination of factors including the breed of dog, symptoms, and physical examination findings.  Stenotic nares can be observed through a routine exam. Further evaluation requires your dog to be lightly anesthetized to assess the soft palate and laryngeal saccules. The diameter of the trachea can be assessed by taking x-rays of the neck and chest.  Advanced testing can include endoscopy or a CT scan of the upper airway.  

How is BOAS treated?

Mild cases can be treated conservatively.  

  • Maintenance of a healthy weight
  • Minimize panting
    1. Avoidance of excessive heat and humidity
    2. Controlled activity 
    3. Minimize stress
  • Use a harness instead of a neck collar

More severe cases require surgical correction. Earlier intervention leads to better outcomes. 

  • A consultation with a veterinary surgical specialist should be considered
  • Stenotic nares can be treated by removing a small wedge of tissue to make the openings larger.  
  • Everted saccules can be removed.  
  • If the soft palate is found to be elongated and is contributing to respiratory problems, it can be shortened. 
  • There is no surgical procedure to correct a hypoplastic trachea.
  • There are anesthetic risks associated with these patients.
  • Surgical risks include bleeding and swelling
    • A temporary tracheostomy may be necessary in some cases

BOAS can become an emergency situation.  If your dog is experiencing a respiratory crisis, immediate transport to your veterinarian or nearest emergency hospital is essential. 

Treatment may include:

  • Sedation 
  • Oxygen therapy
  • Medications to reduce inflammation
  • Tracheostomy (either temporary or permanent) to bypass upper airway obstruction

Other conditions associated with BOAS

  • Laryngeal collapse can occur as a result of chronic upper airway obstruction

  • Bronchial collapse is often associated with laryngeal collapse

  • Gastrointestinal disorders such as hiatal hernia and gastroesophageal reflux can improve following treatment for BOAS

  • Aspiration pneumonia

What are the possible outcomes?

  • Dogs with milder cases of BOAS can have normal life expectancies.
  • Early surgical intervention (dogs under 2 years of age) leads to better outcomes.
  • Dogs with laryngeal collapse have less favorable outcomes, with or without surgery.
  • Dogs with milder or fewer defects have a better prognosis.
  • There are risks of complications including mortality associated with surgery. 


Because this is a genetic condition, dogs that have difficulty breathing, that require surgical therapy, or that have a hypoplastic trachea should not be considered for breeding.