Hematoma is a word most of us have heard at some point in time, in reference to a swelling on a horse or yourself. But what is it, and how does it affect your horse? This article will discuss some of the conditions or diseases in horses that involve hematomas.

A hematoma, from Dorland’s Illustrated Medical Dictionary, is defined as “a tumor containing effused blood” (tumor meaning a benign swelling or mass). Hematomas usually result from bleeding within the body which, as the blood clots, the swelling or hematoma results. Most hematomas are just an indicator of prior hemorrhage and do not need treatment. However, there are other types that indicate severe hemorrhage, such as hematomas within the broad ligament of the uterus in a post-foaling mare or around a fractured long bone. Other hematomas can occur within the upper respiratory tract, which can cause airway obstruction, or on an ovary after ovulation.

Ethmoid Hematoma

One type of hematoma that occurs in the horse is called an ethmoid hematoma. The hematoma is the result of a vascular anomaly within the respiratory tract that is unique to horses. This hematoma is a benign mass that begins within the ethmoid region of a horse’s nasal passage, hence the name. (The ethmoid region of the horse is in the very back recesses of the nasal cavity within the skull, under the sinuses at about the horse’s eye level.) This hematoma is a relatively slow-growing tumor.

Because the tumor begins so deeply within the horse’s nasal cavity, by the time the tumor becomes evident, it usually is quite large and advanced. Horses with ethmoid hematomas will have small amounts of blood or bloody discharge from the nostrils (epistaxsis). This can occur in a horse that is resting or during exercise. In very advanced cases, the tumor will protrude from the nostril of the horse. In these instances, the horse will have some difficulty breathing, especially while exercising, as the tumor is obstructing half of the horse’s airway. Remember, horses cannot breathe through their mouths as humans do