Accidents happen, especially where horses are concerned, so it’s not uncommon for trauma and bruising to occur through a kick, a fall or a collision with an object such as a gatepost. As a result, we can suddenly discover a large, soft lump on some part of the horse’s body — typically the hindquarters, chest or ribs.

The skin might not be broken but one or more of the blood vessels beneath are damaged and bleeding. This blood can fill the space between the damaged tissue and the overlying skin, forming a swelling called a haematoma. The swelling will grow until the pressure that builds up from the fluid accumulation halts the bleeding, allowing a clot to form in the ruptured vessel. Blood pressure is, therefore, an important factor in determining the eventual growth and size of the haematoma.

Since arteries have a higher blood pressure than veins, the haematoma caused by the rupture of an artery will be larger — until sufficient back pressure develops to stop the artery losing blood.

If the haematoma continues to expand and is not being confined to a limited area, your vet may advise an operation to identify the haemorrhaging vessel and ligate it (tie it off).

Haematoma

Most of the time, haematomas are best left alone to resorb (absorb again) — a process that can take weeks or even months. Sometimes, however, your vet will drain the swelling, a decision that will depend on how big it is, how long it has been there and whether the growth is interfering with the horse’s ability to move.

The presence of the haematoma may occasionally disguise a more important injury sustained in the same trauma, such as torn muscle tissue that typically occurs if a limb gets caught. Such involvement of deeper tissues, most common on the inside of the hindlegs or the large muscles of the hindquarters, would be confirmed by ultrasonography.

Stallions kicked during breeding can present with a rapidly developing haematoma in the scrotum, an injury rendered even more serious should it mask the presence of a ruptured testicle.

Drainage dilemma

The haematoma will generally reach a mature or static state around two weeks after formation, when the ruptured vessel has clotted and stabilised. Over time the clot will begin to resolve, resulting in a serum pocket of straw-coloured fluid that should shrink steadily over the coming weeks or months as the fluid is gradually resorbed.

Some haematomas will fail to reduce in size, even after a period of several months. Intervention by way of drainage may be considered in these cases. This should not be done until the haematoma is mature and the damaged vessels have sealed, however, because to do so risks kick-starting the haemorrhage.

Attempting to drain a haematoma with a needle is not without risks and is usually only considered if the haematoma is large, if it is causing some sort of mechanical problem (impairment of movement) or is located where there’s danger of injury from tack or surroundings.

The swelling may well reappear after the contents of the pouch have been removed, because the skin over the pocket is no longer attached to the underlying tissue and the space refills with serum. Even more concerning is that most haematomas are sterile, with very little pain or inflammation, yet draining may introduce bacteria. With blood and serum being the perfect medium for bacterial growth, this may result in a painful abscess replacing the once sterile, painless swelling.

Another form of drainage is to make an incision at the lower portion of the swelling, creating an open wound that allows any fluid to escape. This encourages the pocket to heal from the inside out, through contraction of the surrounding tissues.

Under pressure

If you see the injury occur, you can help control the bleeding (and therefore keep the swelling substantially smaller) by applying direct pressure with a towel — providing it is in an area where the horse will tolerate this and it is safe to do so.

A large haematoma formed on this pony’s chest following surgery to remove a large lump…

Pressure applied in this way should help the haemorrhaging vessel to stop and can make a significant difference by limiting the size to which the haematoma develops. It will also affect the rate at which the fluid is eventually resorbed and the issue resolved.

Cold-hosing the area for 20 minutes at a time, with an hour between sessions, can also be helpful. Only persist with these techniques, however, if the horse is in an unexcited state. Any elevation in his blood pressure due to stress will defeat the purpose.

…and the haematoma was drained. This isn’t always the favoured option, as there is a risk of introducing bacteria and causing an abscess

Cold therapy should be continued intermittently for as long as the area feels warm and soft. When the haematoma has stabilised and the swelling feels as if it is filled by gel rather than free fluid, the application of warm packs and regular gentle massage can help increase the circulation and speed healing. Exercise should be limited until the haematoma is healing, as the aim of management should be to keep the horse calm and limit movement to avoid disturbing and aggravating the clot.

Once the haematoma has healed, scar tissue may remain for some time due to disruption of the skin and underlying tissues. Occasionally, the area will sweat more readily than normal skin.

Haematomas may be unsightly but are rarely a medical emergency. There are some types, however, that indicate severe haemorrhage — such as those around a fractured long bone.

A form of vascular tumour (relating to cancer of the cells that line the blood vessels, and known as a haemangiosarcoma) can be mistaken for a haematoma. Fortunately, this frequently fatal cancer is very rare. If a swelling considered to be a haematoma does not respond normally to treatment, or continues to grow, your vet may wish to take a biopsy sample of tissue to confirm its exact nature.

Other types of haematoma

Ethmoid tumours are unique to horses and grow slowly in the nasal cavity

Ethmoid

Unique to horses, this haematoma (below) forms in the deepest recesses of the nasal cavities and is actually a relatively slow-growing tumour. By the time it becomes evident, it is usually quite large and advanced, causing small amounts of nasal bleeding or bloody discharge and in very advanced cases protruding from the nostril.

Diagnosis is reached by standing endoscopy and/or X-rays of the skull, along with a biopsy of the swelling. Treatment involves either surgical removal, injection of the haematoma with formalin or one of the newer approaches using lasers.

Uterine Artery

Pressure from foaling can rupture the large uterine artery. Blood then collects within the broad ligament, which runs alongside the artery, forming a haematoma. If the blood does not clot then continued bleeding can lead to a fatal haemorrhage within the abdominal cavity.

The bleeding artery can be difficult to find, so surgery to ligate it is usually not recommended. Treatment involves giving intravenous fluids and blood transfusions, along with appropriate medication to encourage the blood to clot and seal the breach in the vessel. Sadly, many mares suffer from profuse bleeding despite aggressive treatment and are unable to be saved.

If the haematoma does stabilise, it can cause pressure on the broad ligament resulting in pain and signs of colic.

Ovarian

Haematomas on the surface of the ovaries can grow up to 10cm in diameter, yet they produce few outward signs and are usually found during routine reproductive examinations. They occur following ovulation as the follicle fills with blood and usually resolve on their own, although they can remain for two to three months. The breeding ability of the mare is not usually affected.

Ref: Horse & Hound; 3 August 2017