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.

These tumors can be diagnosed via standing endoscopy and/or skull radiographs (X rays). A definitive diagnosis of ethmoid hematoma is made from a biopsy. Treatment involves either complete removal of the tumor from the nasal passage via surgery, or one of the newer treatments involving the use of lasers to destroy the tumor.

Uterine Artery Hematoma

Another type of hematoma that can occur in horses is one that is found after a large blood vessel ruptures within the broad ligament during foaling. This ligament suspends the mare's uterus and contains the large uterine arteries. During the birth process, one of these large arteries can rupture, leading to significant hemorrhage and sometimes resulting in death (see Hemorrhage In Broodmares in The Horse of November 1996, page 33).

When the artery is bleeding, the blood can collect within the broad ligament, leading to a hematoma. The hematoma often can be felt on rectal palpation or seen via ultrasound. If the blood does not clot, then the bleeding continues and the mare can hemorrhage to death within her abdominal cavity. The bleeding arteries are difficult to find, so surgery to ligate it usually is not recommended. The cause of the bursting vessel is unknown, although some veterinarians think a copper deficiency might weaken the vessel and predispose it to rupture when the mare is straining to foal. This has not been proven.

Treatment of the bleeding vessel involves correcting the blood loss via intravenous fluids and/or blood transfusions. Other drugs are given to encourage the blood to clot, sealing the break in the vessel. Unfortunately, many of these mares bleed too profusely and quickly and die despite aggressive treatment. The hematoma itself causes pressure on the broad ligament, and this is painful to the mare, resulting in signs of colic. These signs are followed by signs of shock (cold sweat, pale mucous membranes, and a weak and rapid pulse).

Ovarian Hematomas

Ovarian hematomas do not have outward signs as do the other two examples. These hematomas occur on a mare's ovaries and can be felt by palpation or seen via ultrasound. These hematomas usually are found during routine reproductive examinations and can become fairly large (larger than 10 cm in diameter). These hematomas occur following ovulation as the follicle fills with blood, and they are present on the surface of the ovary. Ovarian hematomas usually resolve on their own, but can remain for two to three months. However, they usually do not affect the breeding ability of the mare.

These are only a few examples of hematomas that can occur in horses. Hematomas can occur just about anywhere in the horse where bleeding occurs. Swellings or hematomas that occur in your horse should be evaluated by your veterinarian to determine their cause and treatment, if necessary.

About the Author

Michael Ball, DVM

Michael A. Ball, DVM, completed an internship in medicine and surgery and an internship in anesthesia at the University of Georgia in 1994, a residency in internal medicine, and graduate work in pharmacology at Cornell University in 1997, and was on staff at Cornell before starting Early Winter Equine Medicine & Surgery located in Ithaca, N.Y. He is also an FEI veterinarian and works internationally with the United States Equestrian Team.

Ball authored Understanding The Equine Eye, Understanding Basic Horse Care, and Understanding Equine First Aid, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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