Small Animal ENT and Sleep Medicine Lab-Brachycephalic obstructive airway syndrome in cats

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Brachycephalic obstructive airway syndrome in cats

Brachycephalic obstructive airway syndrome (BOAS) is commonly seen in brachycephalic breeds of cats such as Persian cats, Himalayan cats and Exotic Shorthairs.

Similar to BOAS in dogs, it is a conformation-related disease associated with upper airway obstruction. The preservation of the "flat-faced" characteristic through selective breeding often causes the compression of their facial features.

Some cats may exhibit abnormalities such as proptosis, obstruction of nasolacrimal duct, stenotic nares and malocculation. Other symptoms including nasal congestion sounds, occational mouth breathing, and exercise intolerance.

Pathogenesis
Clinical symptoms
Clinical diagnosis
Treatment and prevention
Pathogenesis
Brachycephalic obstructive airway syndrome (BOAS) is commonly seen in brachycephalic breeds of cats such as Persian cats, Himalayan cats and Exotic Shorthairs. Similar to BOAS in dogs, it is a conformation-related disease associated with upper airway obstruction.

The preservation of the "flat-faced" characteristic through selective breeding often causes the compression of their facial features. Some cats may exhibit symptoms such as corneal ulcer caused by proptosis, epiphora caused by obstruction of nasolacrimal duct, stenotic nares and malocculation.

Pathogenesis for BOAS in cats is the abnormal development of their skulls, in which during the developmemt of the skulls, the basicranial and coronal epiphyseal cartilage closed earlier than other breed kinds. Hence, the facial part of the skull (ex: nasal bones, maxillary bones ) will shorten, causing the compression of the face. This extreme breed selection gives rise to cats that have lost their normal facial structure.

Comparison of head phenotypes between the peke-face Persian (A, B) and the doll-face Persian (C, D). The doll-face Persian has large, round eyes and a small nose, while the peke-face Persian has narrow, elongated eyes and a slightly pronounced muzzle (Schmidt et al., 2017).

Schmidt, M. J., Kampschulte, M., Enderlein, S., Gorgas, D., Lang, J., Ludewig, E., ... & Ondreka, N. (2017). The relationship between brachycephalic head features in modern Persian cats and dysmorphologies of the skull and internal hydrocephalus. Journal of veterinary internal medicine, 31(5), 1487-1501.

Comparison of craniofacial morphologies between the doll-face Persian cats (A, C) and peke-face (B, D). Note the reduction in facial bone size in doll-face Persians. The brachycephalic cranium shape (wide and narrow) is due to premature closure of the coronal suture in these cats (Schmidt, 2019).

Schmidt, M., & Ondreka, N. (2019). Hydrocephalus in animals. Pediatric hydrocephalus, 53.

Four levels of brachycephalic cats are classified by their phenotypic appearance, ranging from mild (I) to severe (IV) (Schlueter et. al., 2009).

Schlueter, C., Budras, K. D., Ludewig, E., Mayrhofer, E., Koenig, H. E., Walter, A., & Oechtering, G. U. (2009). Brachycephalic feline noses: CT and anatomical study of the relationship between head conformation and the nasolacrimal drainage system. Journal of feline medicine and surgery, 11(11), 891-900.

Brachycephalic cats exhibit cranial compression, leading to the disappearance of nasal bone, reduction in the maxilla bone and lacrimal bones, and nearly horizontal alignment of canine teeth (Schlueter et. al., 2009).

Schlueter, C., Budras, K. D., Ludewig, E., Mayrhofer, E., Koenig, H. E., Walter, A., & Oechtering, G. U. (2009). Brachycephalic feline noses: CT and anatomical study of the relationship between head conformation and the nasolacrimal drainage system. Journal of feline medicine and surgery, 11(11), 891-900.

Three-dimensional reconstructions of the skull and teeth in a Domestic shorthair cat (A) and a Persian cat (B) (Sieslack et. al., 2021).

Sieslack, J., Farke, D., Failing, K., Kramer, M., & Schmidt, M. J. (2021). Correlation of brachycephaly grade with level of exophthalmos, reduced airway passages and degree of dental malalignment’in Persian cats. PloS one, 16(7), e0254420.

Malpositioned maxillary canine teeth in brachycephalic cat (Mestrinho et al., 2018).

Mestrinho, L. A., Louro, J. M., Gordo, I. S., Niza, M. M., Requicha, J. F., Force, J. G., & Gawor, J. P. (2018). Oral and dental anomalies in purebred, brachycephalic Persian and Exotic cats. Journal of the American Veterinary Medical Association, 253(1), 66-72.

Nasopharyngeal turbinates in brachycephalic cats (Ginn et al., 2008).

Ginn, J. A., Kumar, M. S. A., McKiernan, B. C., & Powers, B. E. (2008). Nasopharyngeal turbinates in brachycephalic dogs and cats. Journal of the American Animal Hospital Association, 44(5), 243-249.

Use wireframes to explore the relationship between the expressions of different cat breeds and human emotions. Among these breeds, Scottish Fold cats are more likely to exhibit expressions resembling “pain,” evoking feelings of pity in humans (Finka et al., 2020).

Finka, L. R., Luna, S. P., Mills, D. S., & Farnworth, M. J. (2020). The Application of Geometric Morphometrics to Explore Potential Impacts of Anthropocentric Selection on Animals' Ability to Communicate via the Face: The Domestic Cat as a Case Study. Frontiers in Veterinary Science, 7, 606848.
Clinical symptoms
BOAS in cats is slightly different from BOAS in dogs. BOAS in cats is mainly focused on obstruction in upper respiratory tract that is the result of stenotic nares and the growth of soft tissues unproportionately. BOAS-affected cats generally experierence nasal congestion sound, breathing effort or paradoxial breathing. Other symptoms including ocaational mouth breathing and low tolerance towards exercising.

If the obstruction becomes severe, the negative pressure inside the respiratory tract may increase, there is a potential risk of hiatal hernia. The patient may have gastrointestinal symptoms such as vomit or stomach reflux.

Compared to mesocephalic cats, brachycephalic cats are more likely to experience respiratory, gastrointestinal, and exercise issues (Gleason et al., 2023).

Gleason, H. E., Phillips, H., & McCoy, A. M. (2023). Influence of feline brachycephaly on respiratory, gastrointestinal, sleep, and activity abnormalities. Veterinary Surgery, 52(3), 435-445.
Clinical diagnosis
Cats with BOAS (Brachycephalic Obstructive Airway Syndrome) usually come to see the vet because their owners notice symptoms like noisy breathing or open-mouth breathing. When we suspect a brachycephalic cat is affected by BOAS, the next step is to confirm the airway obstruction through examinations, including:

Auscultation for breathing noises (stertor (low-pitch noise), stridor (high-pitch noise), nasal congestion sound)

Nasal examination (visually checking) the narrowness of the nostrils

Doing a slide test to see how clear the nostrils are on both sides

Observing if the cat has inspiratory effort or dyspnea

To confirm an upper airway obstruction, we use imaging tests such as a computed tomography (CT) scan of the head and neck. This allows us to check the nostrils for narrowness, elongated soft palate, or other obstructions relative to the structures.

Additionally, a side-view X-ray of the head and neck, which can be taken without anesthesia, could sometimes show the thick elongated soft palate, but X-ray is not as accurate as a CT scan.

"Auscultation" of the heart, lungs, laryngeal to check for breathing noises.

"Nasal examination" using a penlight to assess the size of the cat's nostrils.

The size of the nostrils from left to right is as follows: normal, mildly stenotic, moderately stenotic, severely stenotic (Anagrius et al., 2021).

Anagrius, K. L., Dimopoulou, M., Moe, A. N., Petterson, A., & Ljungvall, I. (2021). Facial conformation characteristics in Persian and Exotic Shorthair cats. Journal of Feline Medicine and Surgery, 23(12), 1089-1097.

Using a "slide test" to assess the airflow through both nostrils.

Compared to mesocephalic cats (left), brachycephalic cats (right) have absent nasal bones, displaced nasal turbinates, rotated hard palates, smaller airways, and thicker soft palates (Schlueter et. al., 2009).

Schlueter, C., Budras, K. D., Ludewig, E., Mayrhofer, E., Koenig, H. E., Walter, A., & Oechtering, G. U. (2009). Brachycephalic feline noses: CT and anatomical study of the relationship between head conformation and the nasolacrimal drainage system. Journal of feline medicine and surgery, 11(11), 891-900.

CT images of the airway of a brachycephalic cat (requiring anesthesia for imaging), including the nasal alar fold, nasal turbinates, soft palate, and airway (Gleason, 2023).

Gleason, H. E., Phillips, H., Fries, R., Keating, S., Hamel, P., & McCoy, A. (2023). Ala vestibuloplasty improves cardiopulmonary and activity‐related parameters in brachycephalic cats. Veterinary Surgery, 52(4), 575-586.
Treatment and prevention
Unlike brachycephalic dogs, brachycephalic cats commonly suffer from upper airway obstruction due to "narrow nostrils", occasionally accompanied by "nasal turbinate". Therefore, the treatment for narrow nostrils typically involves "ala-vestibuloplasty", performed under anesthesia. This procedure involves removing a portion of nasal alar fold to establish a more open airflow pathway from the inside out. Research showed that ala-vestibuloplasty significantly improves upper airway obstruction in brachycephalic cats, enhancing their breathing, exercise, and feeding abilities, thereby improving their quality of life.

In contrast to brachycephalic dogs, elongated or thickened soft palates are much less common in BOAS-affected cats, so soft palate surgery is not typically a primary treatment option.

Additionally, in daily care, it is important to avoid stressful situations for brachycephalic cats and allow for adequate rest during play to prevent episodes of respiratory distress.

Ala-vestibuloplasty (Techniques：single pedicle advancement flap) (Rahimdoust Mozhdehi et al., 2023).

Rahimdoust Mozhdehi, N., Salari Sedigh, H., & Kazemi Mehrjerdi, H. (2023). Surgical correction of stenotic nares using a single pedicle advancement flap technique in three brachycephalic cats. Veterinary Medicine and Science, 9(6), 2410-2413.

Ala-vestibuloplasty（Techniques：Bilateral wedge resection)(Chen & Chang, 2023).

Chen, Y. C., & Chang, Y. S. (2023). A novel surgical approach for feline stenotic nares: Bilateral wedge resection of the dorsal lateral nasal cartilage in seven cases. Veterinary Medicine and Science, 9(6), 2430-2437.

Ala-vestibuloplasty in brachycephalic cat (removing alar fold).

Photos of ala-vestibuloplasty in brachycephalic cats, showing before, after, and wound healing stages from top to bottom (Schwartz, 2024).

Schwartz, P. (2024). Brachycephalic Obstructive Airway Syndrome in Dogs and Cats. Techniques in Small Animal Soft Tissue, Orthopedic, and Ophthalmic Surgery, 56.

Through owner surveys, it is evident that clinical symptoms such as sneezing, nasal discharge, open-mouth breathing, and snoring decrease in brachycephalic cats after ala-vestibuloplasty surgery (Gleason, 2023).

Gleason, H. E., Phillips, H., Fries, R., Keating, S., Hamel, P., & McCoy, A. (2023). Ala vestibuloplasty improves cardiopulmonary and activity‐related parameters in brachycephalic cats. Veterinary Surgery, 52(4), 575-586.