The nostrils are one of the three unsupported structures in the respiratory tract, the others being the larynx and nasopharynx. The nostrils require active muscular contractions to maintain the patency of their lumen during exercise. The nostrils are a relatively rare site of airflow obstruction. Unilateral facial paralysis is clinically obvious as the horse has a twisted muzzle. This is usually the result of trauma, (kick) which usually causes reversible nerve damage. 

Nostril wounds 

Because the horse has large mobile nostrils, nostril wounds must be carefully apposed – in layers if necessary- to ensure that a cicatrix does not develop which . 

High blowing (false and TRUE nostril flutter) 

In normal horses during exercise, expiratory noises are louder than the inspiratory noises. In high blowing, even louder and more vibratory expiratory noises are made. They are not clinically significant but must be differentiated from other significant respiratory “noises” (incidence - very common) 

False nostril cyst 

In some horses, an epidermoid cyst can develop in the false nostril lining, resulting in facial swelling in the area of the naso-maxillary notch. These swellings do not cause nasal airflow obstructions. Treatment (cosmetic reasons) is by surgical removal of the cyst that can be performed via the false nostril under standing sedation (incidence - rare). 

Rhinitis sicca 

Rhinitis sicca , with accumulations of dry crusty casts on the mucosa of the nostril and nasal cavities often occurs in chronic grass sickness and may cause airflow disturbance with noise production. 

Alar Fold Collapse 

The fleshy alar fold is attached between the ventral concha and false nostril and occasionally (mainly in Standardbred trotters) can collapse into the nasal cavity during fast work and cause airflow obstruction and “noise”. Diagnosis can be confirmed by suturing the alar folds to the nostril bilaterally and assess if this stops noise. If confirmed - resect the alar fold under GA 

Epistaxis (nose bleed)
Non- Traumatic

Spontaneous epistaxis from the nasal vasculature (as occurs in humans), does not occur in the horse. In horses epistaxis is usually due to exercise induced pulmonary haemorrhage (EIPH) and less commonly to haemorrhage from trauma, guttural pouch mycosis or ethmoid haematoma. Endoscopy is the most useful technique for identifying the source of haemorrhage.

The nasal mucosa has a particularly well-developed blood supply. Traumatic epistaxis can occur during naso-gastric intubation or endoscopy, where the instrument has been inadvertently passed into the middle meatus, leading to trauma of the nasal conchae (turbinates) or ethmoturbinates. Epistaxis may also occur from the ventral meatus if an excessively wide tube is used, inadequate lubrication or with excessive horse movement.

Epistaxis occasionally occurs after trauma to the head region (eg after a heavy fall).
Due to a tear of rectus capitis muscles (in guttural pouches) - bleed from the pouches
Or bleeding into the sinuses; a lower grade epistaxis may be evident for 4-6 weeks. Fluid lines will be evident on lateral radiographs.

Endoscopy is of little diagnostic value in recent traumatic nasal epistaxis and may cause further haemorrhage and further distress the animal. Most traumatic nasal epistaxis in horses will cease spontaneously within a few minutes. . A deep bedded dark box, and a closed top door for 15 minutes is a time honoured and effective treatment for traumatic epistaxis! Packing the nose, as is often done for human epistaxis, should only be performed if more than a few litres of blood are shed. 

Nasal neoplasia 

Equine nasal tumours are usually very malignant, e.g. adenocarcinomas or osteogenic sarcomas. And They usually affect older animals. The clinical signs initially reflect local inflammation and secondary infection on and around the tumour and may include chronic unilateral purulent nasal discharge, which may progress to a bilateral discharge, malodorous breath, secondary sinus empyema due to sinus drainage obstruction, unilateral submandibular lymph node enlargement, nasal airflow obstruction, facial (nasal bones) swelling, and halitosis, if the oral cavity is invaded. Endoscopy may demonstrate a mass. Biopsy using trans-endoscopic forceps may obtain a suitable sample for histopathology. Most equine nasal tumours cannot be surgically treated. Radiotherapy can be considered. Euthanasia is indicated if the tumour is advanced (incidence - rare). 

Nasal foreign bodies 

These rare occurrences in horses are usually due to twigs lodging in the rostral nasal cavity. The unilateral clinical signs result from secondary mucosal infection, i.e. a purulent unilateral nasal discharge. Removal of the foreign bodies under direct vision or endoscopically will resolve the problem. 

Nasal mycosis (Mycotic rhinitis) 

In Britain, mycotic rhinitis is usually due to infection with Aspergillus fumigatus or Pseudallescheria boydii but is caused by different agents overseas. The main clinical sign is a unilateral, malodorous, mucopurulent nasal discharge and unilateral lymphadenitis, and occasionally epistaxis. On endoscopy, mycotic rhinitis resembles a ‘mouldy cheese’-like white, yellow or black coloured fungal plaque on the nasal conchae (turbinates) or ethmoturbinates. Confirmation can be made via nasal swabs (or transendoscopic biopsy) with isolation of a heavy pure growth of potentially pathogenic fungus. Remove any large fungal plaques prior to topical therapy with natamycin or enilconazole solutions,. Treatment is usually successful (incidence - uncommon). 

Rostral maxillary cheek apical infection 

Infection of the first 2-3 maxillary cheek teeth usually results in a swelling with a discharging sinus tract on the affected side of the face, rostro-dorsal to the facial crest. A small percentage will, however, discharge medially into the nasal cavity. leading to a unilateral purulent, malodorous nasal discharge. Endoscopy may reveal a purulent granuloma or pus in the rostro-lateral aspect of the middle meatus. The affected tooth should be extracted (incidence - common). 

Wry Nose 

Congenital deformity of the nasal and premaxillary bones (in “wry nose”) can cause displacement of the nasal septum and airflow obstruction. Endoscopy and dorso-ventral radiography will allow further assessment of the deformity. With difficulty and much haemorrhage, these lesions can be corrected by fracture and re-alignment of the premaxillary bone and nasal septum removal (incidence – very rare). 

Progressive Ethmoid Haematoma (PEH)

An ethmoid haematoma is a haemorrhagic polyp with the histological appearance of a haematoma. These lesions, which usually occur in adult horses, generally protrude rostrally into the nasal cavity from the ethmoturbinates, less commonly they grow laterally or dorsally into the sinuses. These lesions bleed in small amounts over very long periods (even years). Mucopurulent as well as haemorrhagic nasal discharge, and possibly airflow obstruction, facial swelling and neurological signs may occur in more chronic cases. PEH are the commonest cause of chronic unilateral epistaxis in the horse. Diagnosis is via endoscopy or sinoscopy and radiography. Repeated, transendoscopic intra- lesional formalin injections appear to offer the best treatment. Surgical excision is traumatic with a less favourable long term prognosis (incidence – rare).
Intra-sinus PEH – see below 

Sinusitis (paranasal sinus empyema) 

Sinusitis is the most common cause of unilateral nasal discharge in the horse. Whilst endoscopy will usually confirm the presence of sinusitis, radiography is more valuable in investigating its extent and aetiology.

Aetiology

(1)Primary (infective) sinusitis (2) Dental apical infection or oro-sinus fistula (3) Maxillary (sinus) cysts (4) Sinus Neoplasia (5) Mycotic sinusitis
(6) Sinus trauma (7) Intra-sinus PEH lesions 

Unilateral purulent nasal discharge, unilateral submandibular lymph node enlargement, possibly unilateral facial swelling, nasal airflow obstruction and/or epiphora, Endoscopy will show discharge emanating from the naso-maxillary aperture (drainage angle). Direct endoscopy of the paranasal sinuses (sinoscopy) is possible through a small external sinus opening made under local anaesthesia, usually into the frontal sinus. 

Primary sinusitis 

The sinuses have poor natural drainage. Mucosal inflammation with URT infections and simultaneous increased mucus production and deciliation of the sinus epithelial cells results in even less effective drainage. If secondary bacterial infection occurs, sinus empyema will develop. This type of sinusitis can transiently occur with upper respiratory infections, but on occasions, mainly due to inspissation of pus especially in the rostral maxillary and ventral conchal sinuses, it may become chronic (>2 months duration). Careful radiological, sinoscopic and clinical examination should be performed. In the absence of an obvious underlying lesion, such a sinusitis may be termed a “primary sinusitis”. Primary sinusitis may clear spontaneously, antibiotics may help some early cases. Sinus lavage via a frontal sinus trephine (for caudal sinuses) and following fenestration of ventral conchal bulla (for rostral 2 sinuses) with an indwelling tubing with lukewarm dilute iodine or saline (9g salt/ 1L water) for 5-7 days should resolve a primary sinusitis. If the pus becomes inspissated, it will require transendoscopic or surgical removal under standing sedation. 

Dental Sinusitis 

Dental sinusitis is caused by infection of the apices of the upper 08s-11s, that lie within the maxillary sinuses. A copious and malodorous nasal discharge is often present (anaerobic bacterial infection) and halitosis will occur if the dental infection involves the clinical crown. Oral examination may show fracture, pulpar exposure or other lesions. Latero-oblique radiographs are of most value and dorso- ventral radiographs outline medial sinus swellings and image the ventral conchal sinus. Computed Tomography is of optimal diagnostic value and scintigraphy is also of value. Extraction of the affected teeth is indicated, preferably by oral extraction. 

Maxillary (Sinus) cyst 

These mucoid filled cysts develop in the maxillary and occasionally in the frontal sinuses. They can occur in all age groups, including foals. Very marked facial swelling and epiphora is a feature of many cases. Confirm diagnosis by lateral and dorso-ventral radiography. Homogenous, rounded radio-dense cysts are sometimes visible, possibly surrounded by fluid lines due to secondary sinus empyema. Surgically remove the cyst using a maxillary bone flap. 

Sinus Neoplasia 

Like nasal neoplasia, there are uncommon lesions that usually affect older animals. They are usually very malignant growths, especially carcinomas. Clinical signs, treatment and prognosis are similar to those of nasal neoplasia. (incidence – rare). 

Mycotic Sinusitis 

Mycotic (usually Aspergillus fumigatus) infections of the paranasal sinuses are usually diagnosed on sinoscopy and respond to sinus lavage with dilute pevidine iodine, natamycin or enilconazole.