WHAT'S THAT lump?

An unexpected swelling on a horse is enough to catch anyone off guard. From how a haematoma forms to helping them heal, Robyn Graham MRCVS tells all

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THE sudden appearance of a large swelling on a horse can be quite alarming to horse owners, but if it is a haematoma, it can look worse than it is.

WHAT IS IT?

A HAEMATOMA is a localised collection of blood specifically (as opposed to a seroma, which is filled with serum, or free blood in a body cavity, which is not trapped in a specific location). Haematomas usually occur within a muscle or between regions of connective tissues and may present as an acute soft swelling of varying sizes on any part of the horse, though are most commonly found on the neck, hindquarters, chest, or abdomen.

FORMATION

HAEMATOMAS can arise from any blunt force trauma, such as a kick or fall, or a collision with solid objects, such as cross-country fences. There may be an associated graze or wound of the skin overlying the affected tissues, or the skin may remain completely intact. Depending on the proximity to the time of trauma, the swelling may be sensitive, warm to the touch or both.

The swelling forms from injury to the soft tissues under the skin and the resulting leakage of blood from damaged blood vessels into the space created by the injured soft tissues. The degree of swelling can vary significantly depending on the exact tissues involved, and the size and number of blood vessels damaged.

The blood will continue to fill the space and the swelling will grow until the pressure that builds up from the accumulated fluid stops the bleeding and a clot forms in the damaged vessel. This is the reason that haematomas resulting from a ruptured artery will be larger than those from a vein, as higher pressures are required to cause a clot to form in the artery.