Diseases of the nasal septum are rare. Most nasal septal disorders are congenital abnormalities that remain undetected until the horse is exercised. Traumatic injury to the bridge of the nose as a juvenile can produce nasal septal deviation and thickening. Other less common diseases of the nasal septum include amyloidosis, fungal infection, and squamous cell carcinoma.
Thickening or deviation of the nasal septum causes low-pitched stertorous breathing during exercise. Facial deformity may be seen. Septal abnormalities may be detected by palpation, visual inspection, and endoscopic examination. Dimensions of the nasal cavity are difficult to appreciate via endoscopic examination; however, abnormalities of the mucosa are easily identified. Precise dorsoventral radiographs of the skull provide definitive evidence of septal deformity, deviation, and thickening. Histologic examination of any nodules or discrete lesions on the septum will identify tumors, amyloidosis, or fungal infections.
Surgical resection of the nasal septum is the only treatment option in most cases. The entire diseased portion of the septum can be excised using obstetrical wire by transecting the septum on the dorsal, ventral, and caudal border. Hemorrhage is substantial during this procedure (4–8 L), and the nasal passages are packed with sterile gauze soaked in saline or in 1:100,000 epinephrine solution to minimize blood loss. Before the horse recovers from anesthesia, a tracheotomy is performed.
Postoperative care includes parenteral antibiotics and NSAIDs. The packing and tracheotomy tube should be removed 48–72 hr after surgery. All incisions heal by second intention within 3 wk. Horses should be rested for ~2 mo before returning to normal activity. After surgery, most horses make a respiratory noise during work, although less than before surgery, and exercise tolerance is improved. Shortening of the upper jaw, incisor malalignment, or nostril collapse can develop if the procedure is performed in immature horses. Ideally, the surgery should be delayed until maturity.
Nasal polyps are pedunculated growths that arise from the mucosa of the nasal cavity, nasal septum, or tooth alveolus. Polyps are usually unilateral and single but can be bilateral and multiple. They form in response to chronic inflammation by hypertrophy of the mucous membrane or exuberant proliferation of fibrous connective tissue. There is no age, breed, or gender predilection.
Clinical signs are poor airflow through the affected nasal passage; inspiratory dyspnea; unilateral, malodorous, mucopurulent nasal discharge; and low-volume epistaxis. The mass may extend rostrally until it protrudes beyond the nostrils. Polyps are detected via endoscopic and radiographic examination, and histopathologic evaluation of biopsy samples provide a definitive diagnosis. Surgical excision is performed via an incision in the false nostril, a trephine opening, or a bone flap.
Choanal atresia is caused by persistence of the bucconasal membrane that separates the primitive buccal or oral cavity from the nasal pits during embryonic development. Bilateral and unilateral cases have been described in horses. Clinical signs are evident immediately after birth in foals with bilateral disease, because dyspnea is severe and air cannot be detected passing through the nostrils. An endoscope or stomach tube passed through the ventral meatus will be obstructed at the level of the medial canthus of the eye.
Bilateral complete choanal atresia is a life-threatening condition, and a tracheotomy must be performed immediately after birth. It may be possible to perforate a thin membrane by electrocoagulation or laser or by excision through bilateral flaps centered along the midline. Indwelling tube stents should be inserted through both choanae and left in place for 6 wk.