Choanal atresia is caused by the bucconasal membrane, a membrane that separates portions of the mouth and nose during fetal development but is normally gone by birth. In choanal atresia, the membrane is still present at birth and one or both nostrils are partially or completely shut off from the rest of the respiratory system. Clinical signs are evident immediately after birth in foals in which both nostrils are affected, because labored breathing is severe and air cannot be detected passing through the nostrils. This is a life-threatening condition. Immediately after birth, a tube must be inserted through the neck into the trachea (tracheotomy) to allow the foal to breathe until the condition can be corrected. The situation is less severe if only one nostril is affected.
Diseases of the nasal septum (the “wall” between the nostrils) are uncommon. A traumatic injury to the bridge of the nose of a young horse can produce nasal septal deviation and thickening. Other less common diseases of the nasal septum include fungal infection and squamous cell carcinoma (a type of cancer). Thickening or deviation of the nasal septum causes low-pitched noisy breathing during exercise. Facial deformity may be observed. Your veterinarian may be able to detect septal abnormalities by physical examination or endoscopic examination. X-rays of the skull can provide evidence of septal deformity, deviation, and thickening. Microscopic examination of any nodules or lesions on the septum will identify tumors, amyloidosis, or fungal infections.
Surgical repair of the nasal septum is the only treatment option in most cases. The incisions heal in a few weeks, but horses should be rested for about 2 months before returning to normal activity. After surgery, most horses make breathing noise during work, although less than before surgery, and exercise tolerance is improved. Shortening of the upper jaw, poor alignment of the incisors, or nostril collapse can develop if the procedure is performed in immature horses, so the surgery should be delayed until the horse has reached maturity, if possible.
Nasal polyps are noncancerous growths that arise from the mucous membranes of the nasal cavity, nasal septum, or tooth socket. Polyps are usually single but can be multiple. They form in response to chronic inflammation by excess growth of the mucous membrane or fibrous connective tissue. They occur in all ages and breeds of horses.
Signs include poor airflow through the affected nasal passage, labored inhalation, a bad-smelling nasal discharge containing mucus and pus, and low-volume bleeding from the nose. The polyp may extend until it protrudes beyond the nostrils. Polyps are detected via endoscopic and radiographic examination, and microscopic evaluation of tissue samples provide a definitive diagnosis. They can be removed surgically.
Also see professional content regarding disorders of the nasal passages in horses.