English
As horse owners are well aware, equines are susceptible many forms of gastrointestinal disease. One such concern is strangulating lipomas, which pose a serious risk of gut dysfunction in horses.
A lipoma is a tumor made of fat cells and can develop anywhere in the body. Lipomas are common in aging mammals and are often harmless.
Strangulating lipomas are a subtype that pose a much more serious risk to horses. When a lipoma arises from the outer layers of the gastrointestinal tract, it can grow until it wraps around the entire circumference of the tract, cutting off blood supply.
If blood flow in the gut is significantly restricted, it can result in tissue death and permanent damage. In severe cases, strangulating lipomas can be fatal.
Horses over the age of 15 are at greater risk of developing strangulating lipomas, as are geldings and certain breeds.
Surgery is the main treatment for strangulating lipomas. Prognosis varies depending on how invasive the lipoma surgery is, but mortality rates of strangulating lipomas are high.
Strangulating Lipomas in Horses
A strangulating lipoma is a ball of fat at the end of a long tether of tissue that has become wrapped around a part of the horse’s digestive system, cutting off the blood supply. [1]
A lipoma is a benign (non-cancerous) fat tumor that develops between layers of tissue in the mesentery, the fan-shaped organ that loosely anchors the digestive system to the rest of the body. [1][2]
Lipomas that remain in place are not usually a problem, but in some cases the tissues they are housed in begin to stretch under their weight. [1] The stretched tissue gets pulled further from its starting point due to the weight of the growing tumor, eventually becoming a bola – a ball at the end of a long tether. [1][2]
The tether of tissue that stretches from the mesentery to the lipoma is called a peduncle (also referred to as a pedicle or stalk). [1][2] When a lipoma forms a peduncle, it is called a pedunculated lipoma. [1]
When the structures near the lipoma get tangled in the peduncle they can become incarcerated – trapped in a knot of tissue. [1] This typically occurs in the small intestine, but can also involve the colon, part of the mesentery itself, or in very rare cases, the cecum. [1][3][4]
Incarceration occurs either when the lipoma travels around inside the body cavity and encircles structures, or because movement of the GI tract allows adjacent structures to fit behind the stalk where they become trapped. [2]
If the intestine or another structure caught up in the pedunculated lipoma is wrapped tightly enough to cut off blood supply, it is referred to a strangulating lipoma. [1] If the blood supply to these structures is disrupted for too long, the tissue trapped inside begins to swell, making it impossible for the structure to free itself. [3] Eventually, if blood supply is cut off completely, the tissue dies. [3]
Risk Factors
Strangulating lipomas are one of the more common causes of colic in horses that require surgery. [5][1]
Older horses are more likely to develop strangulating lipomas. [1][4] Horses older than 15 years have a very high likelihood of developing lipomas. [4]
Geldings are more likely than stallions or mares to develop strangulating lipomas. [1][5] This is possibly due to increased food intake and decreased activity associated with castration in horses. [1] Obesity may also play a role in the development of strangulating lipomas. [1]
Some breeds are particularly susceptible to strangulating lipomas, including: [1]
Horses that are insulin resistant also have a higher risk of lipomas. [1]
Severity
The severity of a strangulating lipoma depends on which structure is incarcerated, how much tissue is trapped, for how long, and to what degree. [2] In some cases, only a small piece of intestine or colon becomes incarcerated. [2] In other cases, long sections become trapped. [2]
Two or more loops from different sections of the intestine can also become trapped by a single lipoma. [2]
The intestine can also become incarcerated by a pedicle without it being strangulated. [2] This means that blood is still able to get to the portion of the intestine that is trapped, and no tissue death takes place. [4] However, in cases where a structure is completely obstructed, the blood supply is cut off and tissue death occurs. [5]
Lipomas can develop in the mesentery and never develop a peduncle, and some develop a peduncle but never trap another organ. [1]
Other factors influencing potential severity include: [1][4]
- Peduncle length
- Lipoma weight
- Presence of single vs. multiple lipomas
Although there is considerable variation in the character of pedunculated lipomas, once a structure in the gastrointestinal tract loses significant blood supply due to strangulation, the prognosis for the horse is poor even with appropriate medical intervention. [5]