Horses with evidence of epistaxis can be challenging to diagnose and manage. The volume of visible blood can range from a
trace of serosanguinous discharge that is suggestive of a past episode of bleeding, to high volume fresh blood flow from both
nares. The occurrence can be sporadic and intermittent or sudden, continuous and fatal in a short period of time. Epistaxis
can be secondary to hemorrhage arising from anywhere along the respiratory tract. Unilateral epistaxis tends to arise from
somewhere rostral to the caudal extent of the nasal septum, i.e. from the ipsilateral nasal passage/paranasal sinus region.
Bilateral nasal epistaxis is typically from a lesion caudal to the end of the nasal septum but occasionally the lesion will
be located in the caudal nasal passage on one side and blood tracks down both nasal passages. Successful treatment of the
cause of epistaxis depends on an accurate and timely diagnosis. Respiratory tract endoscopy and radiography remain the key
imaging modalities to facilitate most diagnoses. Biopsy of masses is also required for definitive diagnosis in many cases.
Awareness of the causes of nasal epistaxis and classic history and clinical signs are useful to formulate a differential diagnosis
and determine if a case represents an emergency. This paper will describe the causes of nasal hemorrhage moving from the upper
to the lower respiratory tract. Iatrogenic causes of nasal hemorrhage are not discussed (for example, nasogastric intubation
trauma, and surgical trauma).
Upper Respiratory Tract Origin
Idiopathic Mucosal Bleeding
Rarely, or perhaps more commonly than appreciated, a steady or intermittent low flow nasal bleed will arise from a leaking
mucosal vessel in the nasal, paranasal or nasopharyngeal wall. Historically these horses are reported to have spontaneous
epistaxis of very small volume, sometimes related to exercise. The bleeding often stops and then recurs intermittently days,
weeks or months apart. Veterinary attention is sought when the bleeding persists or is more frequent in occurrence. Diagnosis
is completely dependent on endoscopic visualization of the source of bleeding from a mucosal surface. Use of a pediatric endoscope
allows thorough examination of the nasal conchal surfaces where access into the recesses of the nasal meati is too tight for
a standard 9-10 mm diameter endoscope to pass without traumatizing the tissues. Active bleeding must be present to find the
source of this hemorrhage. A single vessel rupture, sometimes with a low pulsatile flow if a small arterial branch is damaged,
or a diffuse oozing of blood from a small surface area of the mucosa has been seen. These cases have been successfully treated
by cauterizing any accessible bleeding vessel/mucosa with silver nitrate sticks or laser ablation. 
