Brachycephalic Airway Obstruction Syndrome (BAOS)
in the Cavalier King Charles Spaniel
- Symptoms
- Care and Treatment
- Elongated Soft Palate
- Stenotic Nares
- Everted Laryngeal Saccules
- Laryngeal Collapse
- Breeders' Responsibilities
- Current Research
- Related Links
- Dedication
- Veterinary Resources
Brachycephalic airway obstruction syndrome (BAOS), also referred to as brachycephalic airway disease (BAD) and brachycephalic airway syndrome (BAS), is an inherited condition in the Cavalier King Charles spaniel. The breed is pre-disposed to it, due to the comparatively short length of the Cavalier's head and a compressed upper jaw*.
The term "brachycephalic" or "brachiocephalic" means short-nosed and refers to dogs with short muzzles, noses, and mouths. "Brachy" means short and "cephalic" means head. The throat and breathing passages in brachycephalic dogs often are undersized or flattened. The head's soft tissues are not proportionate to the shortened nature of the skull, and the excess tissues tend to increase resistance to the flow of air through the upper airway (nostrils, sinuses, pharynx and larynx).
This developmental defect is somewhat more apparent in a few other breeds: the English bulldog, pug, Boston terrier, and Pekingese, in particular. However, various degrees of BAOS predominate in the CKCS. The primary BAOS abnormalities in the Cavalier include an elongated and fleshy soft palate, narrowed nostrils (stenotic nares), and everted laryngeal saccules, all of which are discussed in detail here. Other disorders may include laryngeal malformation and relatively small windpipe (tracheal hypoplasia or stenosis) and collapsing trachea**, which are not specifically covered in this article. All of these disorders cause obstruction of the upper airway, compromise the dog's ability to take in air, and may result in laryngeal collapse.
* There is some argument among researchers as to whether
the Cavalier King Charles spaniel is a brachycephalic breed or a mesaticephalic
(or mesocephalic)
breed. Regardless, the CKCS is pre-disposed to the brachycephalic breathing
difficulties described in this article.
** Trachea collapse in the Cavalier King Charles spaniel may also be due to an
enlarged heart caused by advanced mitral valve disease. Also,
a 2004 study by researchers at the Royal
Veterinary College found that 53% of the brachycephalic dogs in their 92 dog
sample had heart disease, compared to 24% of the non-brachycephalic dogs.
See
Mitral Valve Disease.
Overall Symptoms
The symptoms may vary and range in severity, depending upon which abnormality is causing them, but they typically include labored and constant open mouthed breathing, noisy breathing, snuffling, snorting, excessive snoring, gagging, retching, exercise and/or heat intolerance, general lack of energy, pale or bluish tongue and gums due to a lack of oxygen.
Also, studies have concluded that brachycephalic dogs may be predisposed to the conditions of Primary Secretory Otitis Media (PSOM), and eye problems, such as entropion, dry eye, and other disorders which may be caused by eyes not properly seated in the skull.
Overall Care and Treatment
The brachycephalic Cavalier is an inefficient panter. Increased panting can cause swelling and narrowing of the airway, resulting in collapsing or fainting. The excessive panting and episodes of other symptoms may place increased strain on the dog's heart, which Cavaliers with mitral valve disease cannot afford to risk.
Care should be taken to avoid overheating and excessive excitement and excessive exercise, which may cause increased panting. Excessive barking or panting may cause the throat to swell, which could result in a totally blocked airway. Most importantly, the owner should not let the dog get too hot, particularly in the summer months, and not allow the dog to become overweight, as obesity will exacerbate the respiratory difficulties. Death from such related causes as heat stroke may be the consequence of not diagnosing and treating these symptoms early enough.
In mild episodes, calming and cooling the dog may be sufficient. Inflammation and swelling of the airway tissues (oedema) may be treated with oxygen therapy and corticosteroids for short term relief. Surgery is required when the abnormalities chronically interfere with breathing. Following surgery, the dog will need to be monitored closely for at least the first 24 hours, because inflammation or bleeding can obstruct the airway, making breathing difficult or impossible.
Elongated Soft Palate
-- what it is
The
palate is the roof of the mouth. It is divided into two parts, the anterior bony
hard palate, and the posterior fleshy soft palate. The soft palate separates the
nasal passage from the oral cavity. An elongated soft palate is too long for the
length of the mouth, so that its tip protrudes into the front of the airway and
may get sucked into the laryngeal opening where it may obstruct the normal
passage of air into the trachea.
-- symptoms
The most common and recurrent symptom of an elongated soft palate is noisy breathing. Occasionally, the dog will make snorting sounds, which is due to the tip of the palate flapping into the trachea during respiration. This is called the "Cavalier snort" or a "reverse sneeze". The dogs also are more likely to snore, gag, or retch, and in severe instances, they may collapse if the airflow is obstructed completely.
-- diagnosis
In severe cases, the palate usually is examined with the dog under light general anesthesia, using a laryngoscope. An elongated palate will obstruct the view of the larynx when the tongue is depressed. The veterinarian may take an x-ray to determine the length of the palate and airway.
-- treatment
If the palate is only moderately elongated and does not totally block the trachea, snorting may be relieved by forcing the Cavalier to breathe through its mouth instead of its nose. This may be done by holding the dog's head down and mouth open with one hand while blocking air from entering the nose with the other hand.
Treatment for recurring blockage of airflow is surgical removal of excess tissue from the palate by a veterinary surgeon. Post surgery prognosis is good for young dogs. They generally may be expected to breathe much easier, with significantly reduced respiratory distress, and display more energy and stamina. Older dogs may have a less favorable prognosis.
Stenotic Nares
-- what they are
Stenotic nares are abnormally narrow or obstructed nostrils, especially when inhaling. Dogs with this disorder tend to breathe primarily through their mouths, because breathing through the nose is unproductive. When they do breathe through their noses, they make wheezing sounds. Stenotic nares cause the dog to inhale deeper to draw air through the nose and into the lower airway, which may contribute to the development of secondary abnormalities, such as everted laryngeal saccules and laryngeal collapse.
-- symptoms
The dog's nose appears narrow, with the nostril wings (alar folds) collapsing inward during inhalation and possibly blocking the nares. As noted above, the dog tends to breathe through its mouth, and makes wheezing sounds when breathing with its mouth closed. Symptoms typically include labored and constant open mouthed breathing, noisy breathing, snuffling, snorting, excessive snoring, and in severe cases, gagging, retching, exercise and/or heat intolerance, pale or bluish tongue and gums due to a lack of oxygen.
-- diagnosis
Stenotic nares are easily diagnosed by visual examination. In severe cases, the flow of air through the nostrils may be so poor that no air movement can be detected.
-- treatment
Surgery under general anesthesia is the preferred means of treating stenotic nares. The aim is to increase the size of the nostrils by removing tissue from the wings and possibly some related cartilage. Post surgery recovery is similar to that described above under Overall Care and Treatment and treatment for elongated soft palate. Following surgery, the dog will be required to wear an Elizabethan collar to keep the surgical site clean and to protect it from rubbing.
Everted Laryngeal Saccules
-- what they are
Everted laryngeal saccules are a secondary abnormality to either an elongated
soft palate or stenotic nares. The larynx contains the vocal chords, produces
sound, and protects the trachea. It is located at the point where the upper
tract divides into the trachea and the esophagus. During swallowing, the larynx
closes to prevent swallowed material from entering the lungs. The laryngeal
saccules are part of the mucosal lining of the laryngeal ventricles and appear
as two membranous sacs that are located in recessions in front of the vocal
folds.
Brachycephalic Cavaliers must create more pressure when they inhale in order to fill their lungs with air. This decreases the pressure in the upper airway, causes the lining of the larynx (laryngeal ventricles) to swell, and forces the laryngeal saccules to vibrate and evert into the airway at the opening to the trachea, blocking the flow of air. Everted laryngeal saccules usually are the first stage of laryngeal collapse.
-- symptoms
The symptoms are those common to a lack of air intake, such as gagging, retching, fainting, pale or bluish tongue and gums due to a lack of oxygen.
-- diagnosis
Everted laryngeal saccules are diagnosed under anesthesia. They appear as bilateral, red, fleshy, globular sacs.
-- treatment
Tissue from the saccules are surgically removed under general anesthesia. A tube will be inserted through the neck into the trachea (“temporary tracheostomy”) to allow an airway during surgery and will remain until the swelling in the throat subsides enough that the dog can breathe normally. Post surgery and recovery are similar to that described above under under Overall Care and Treatment and treatment for elongated soft palate.
Laryngeal Collapse
-- what it is
Laryngeal collapse is an advanced form of brachycephalic airway obstruction syndrome. The primary conditions of stenotic nares and elongated soft palate, together with everted laryngeal saccules, lead to abnormal stresses on the larynx and a progressive distortion and ultimate collapse of the cartilage supporting the larynx. There are three stages of laryngeal collapse, Stage 1 being the everted laryngeal saccules described above. Stage 2 occurs when the arytenoid cartilage loses its rigidity and gradually collapses inwardly. The third and final stage is when the cartilage fails completely, and the larynx collapses.
-- symptoms
When the larynx collapses, the Cavalier will not be able to breathe at all. The situation will be an extreme, life-threatening emergency.
-- diagnosis
The diagnosis is made by visual examination while the dog is under light anesthesia.
-- treatment
Depending upon the severity of the collapse, an early option may be a partial laryngectomy to enlarge the laryngeal opening. The procedure will include anesthesia and a temporary tracheostomy. Statistical studies have shown that less than 50% of dogs treated this way survive, due to the permanent cartilage deformation and softening which results in continued collapse. Permanent tracheostomy is the only other option. Prognosis is poor, particularly for older dogs.
Breeders' Responsibilities
BAOS is a consequence of the conformation standards for the CKCS. Cavaliers with significant breathing difficulties or that have required surgery to correct airway obstruction, should not be used for breeding.
Current Research
4July 2010: UK researchers find association between PSOM and brachycephalic conformation in Cavaliers. In their report, they find, "in CKCS, greater thickness of the soft palate and reduced nasopharyngeal aperture are significantly associated with OME [otitis media with effusion, meaning PSOM]."
Related Links
Primary
Secretory Otitis Media
Entropion
Syringomyelia
Elongated Soft Palate -- ACVS Website
Stenotic Nares Surgery -- ACVS Website
Everted
Laryngeal Saccules Surgery -- ACVS Website
Laryngeal Collapse -- ACVS Website
Dedication
This article is dedicated to a six year old male Cavalier King Charles Spaniel named Callie, who died in June 2006 of heat stroke due to BAOS after a brief walk with his owner in 79º weather in California, and to a six year old female Cavalier named Bafi (right), who died in September 2007 from BAOS in Israel.
Veterinary Resources
Upper airway obstruction surgery. Harvey C.E. J. Amer. Animal Hosp. Assn. 18: 538–544 (1982). Included CKCS.
Brachycephalic airway obstructive syndrome. Wykes PM. (1991) Problems in Veterinary Medicine 3, 188–197.
"Recognition and treatment of congenital respiratory tract defects in brachycephalics.". Hendricks, JC In Kirk's Current Veterinary Therapy XII Small Animal Practice. p. 892-894. .JD Bonagura and RW Kirk (eds.) 1995. W.B. Saunders Co., Toronto.
Brachycephalic airway obstruction syndrome – a review of 118 cases. Lorinson D., Bright R.M. and White R.A.S. Canine Practice 22: 18–21 (1997). Included CKCS.
Temporomandibular joint morphology in Cavalier King Charles spaniels. Alison M. Dickie, Tobias Schwarz, Martin Sullivan. Vet. Rad. & Ultra; May 2002; 43:260
"Brachycephalic airway syndrome." Monnet E. In: Textbook of Small Animal Surgery, 3d Ed. vol. 1, pp.808–813. D Slatter, ed. (2003) WB Saunders, Phila.
Breed Predispositions to Disease in Dogs & Cats. Alex Gough, Alison Thomas. 2004; Blackwell Publ. 44-45. Quote regarding CKCS: "Brachycephalic upper airway syndrome -- complex of anatomical deformities -- common in this breed -- a likely consequence of selective breeding for certain facial characteristics."
Material in the middle ear of dogs having magnetic resonance imaging for investigation of neurologic signs. Owen MC, Lamb CR, Targett MP. Vet. Radiology & Ultrasound, Mar 2004, 45(2):149-155.
Brachycephalic Airway Syndrome. Eric Monnet. WSAVA Proceedings 2004
Differences between breeds of dog in a measure of heart rate variability. Doxey S, Boswood A. Vet Rec. 2004 Jun 5;154(23):713-7.
"Brachycephalic airway disease." Dottie Brown, Sue Gregory. In: BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery. Daniel Brockman and David Holt, eds. Oct. 2005. Quote: "Breeds particularly predisposed to BAD [brachycephalic airway disease] with elongation of the soft palate include the Bulldog, Pug, Boston Terrier and, in the UK, the Cavalier King Charles Spaniel."
Results of surgical correction of abnormalities associated with brachycephalic airway obstruction syndrome in dogs in Australia. C. V. Torrez and G. B. Hunt. J.Sm.Anim.Prac. March 2006; 47(3):150. Quote: "Stenotic nares were present in 31 dogs (42·5 per cent), elongated soft palate in 63 (86·3 per cent) and everted laryngeal saccules in 43 (58·9 per cent). The most common breeds were the pug (19 dogs, 26 per cent), Cavalier King Charles spaniel (15 dogs, 20·5 per cent), British bulldog (14 dogs, 19·2 per cent) and Staffordshire bull terrier (4 dogs, 5·5 per cent). Laryngeal collapse was present in 34 of 64 (53 per cent) dogs. ... Clinical Significance: Laryngeal collapse is relatively common in dogs presented for surgical correction of brachycephalic airway obstructive disease. Dogs with severe laryngeal collapse often respond well to surgery. Clinical signs rarely resolve completely following surgery."
Surgical correction of brachycephalic syndrome in dogs: 62 cases (1991–2004). Todd W. Riecks, DVM; Stephen J. Birchard, DVM, MS, DACVS; Julie A. Stephens, MS. J.Amer.Vet.Med.Assn. May 1, 2007, 230( 9): 1324-1328. Included CKCS. Quote: "Elongated soft palate was the most common abnormality (54/62 [87.1%] dogs); the most common combination of abnormalities was elongated soft palate, stenotic nares, and everted saccules (16/62 [25.8%] dogs). ... Surgical treatment of brachycephalic syndrome in dogs appeared to be associated with a favorable long-term outcome, regardless of age, breed, specific diagnoses, or number and combinations of diagnoses."
Canine Inherited Disorders Database: www.upei.ca/cidd/Diseases/respiratory%20disorders/brachycephalic%20syndrome.htm Quote: "These problems are generally most common and severe in the English bulldog. Other brachycephalic breeds in which this syndrome is found include the pug, Boston terrier, Pekingese, Cavalier King Charles spaniel, Chinese shar-pei, French bulldog, Lhasa apso, and shih tzu."
Brachycephalic Syndrome: New Knowledge, New Treatments. Gilles Dupre. 2008 WSAVA Congress. Quote: "Brachycephalic breeds are usually distinguished from others by their shortened skull which results from an early ankylosis of the cartilages in this region. Different breeds are usually recognized as brachycephalic: Boston terrier, English and French bulldog, pugs, Pekinese, Shih-tzu and cavalier King Charles." www.vin.com/proceedings/Proceedings.plx?CID=WSAVA2008&PID=pr23882&O=Generic
Relationship between pharyngeal conformation and otitis media with effusion in Cavalier King Charles spaniels. Hayes GM, Friend EJ, Jeffery ND. Vet Rec. 2010 Jul 10;167(2):55-8. Quote: "Otitis media with effusion (OME) is a common incidental finding in otherwise normal Cavalier King Charles spaniels (CKCS). In this study, measurements made on MRI were used to determine whether there was an association between OME and brachycephalic conformation. The results confirm that association and also demonstrate that, in CKCS, greater thickness of the soft palate and reduced nasopharyngeal aperture are significantly associated with OME. These results suggest that auditory tube dysfunction and OME may represent a previously overlooked consequence of brachycephalic conformation in dogs."
