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]

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Impact of Lipoma Location

In cases where strangulation occurs, the vast majority (90%) involve the small intestine. [3] Typically, it is the middle part of the intestine, the jejunum, which becomes entangled. [4]

Other parts of the horse’s digestive system can develop lipomas and are at some risk of strangulation. Pedunculated lipomas do occasionally arise from the mesentery that is attached to the small colon. [1] In these cases, it is less likely to result in strangulation. [2]

The small colon has a different anatomy, weight, mobility, and contents from the small intestine, which influences the way it interacts with pedunculated lipomas when present. [2]

In rare cases, a part of the mesentery itself is strangulated. [1][2][3] In mesentery strangulation, the small intestine and small colon may be unaffected because the blood supply to these structures comes from many branches. Cutting off supply to some of these structures may not prove catastrophic to the attached organ if the other supply vessels are still working normally. [3]

In very rare cases, the cecum is strangulated. [4] In most cases, the lipoma forms in the mesentery. [2] In other cases, it forms in the omentum. [2]

Causes

Some pedunculated lipomas do no harm while others travel in the body cavity, trapping and strangulating one or more loops of intestine. This can cause catastrophic injury to the horse and even lead to death. [1] 

The conditions that lead to the development of strangulating lipomas and determine whether involved structures will become permanently damaged are unknown at this time. [1]

Factors that affect whether a pedunculated lipoma is likely to get tangled with another structure include the location, the length of the peduncle, and the weight of the lipoma. [2]

Lipomas that develop close to the junction between the intestine and the mesentery are less likely to trap the intestine. [2] Lipomas that are heavier than 33 grams (1.2 oz) are more likely to incarcerate another structure. [2] The longer the peduncle and the heavier the lipoma, the more likely incarceration is to occur. [2]

In rare cases two pedunculated lipomas develop and wrap around each other. [4]

In the case of large lipomas with short peduncles, disease may result from compression of an organ under the weight of the mass, not from incarceration of the organ. [1][4] Pain and colic in these cases may also be the result of the stretching of the mesentery. [2]

Symptoms

The most common symptom of strangulating lipoma is colic. [1] Mild to severe abdominal pain usually develops within 24 hours of strangulation. [3] It’s important for horse owners to familiarize themselves with all of the hallmark signs of colic, including:

  • Rolling
  • Biting at the flanks
  • Sweating
  • Groaning
  • Restlessness and agitation

Other symptoms specific to strangulating lipoma include: [4][6]

  • Distention of the stomach
  • Increased heart rate
  • Absence of stomach noises (borborygmi)
  • Fatigue
  • Signs of dehydration including tacky gums
Colic is a medical emergency requiring urgent veterinary attention. Early intervention provides the best chance of a positive outcome for the horse.

Diagnosis

Depending on the severity of symptoms, affected horses may need to be sedated before diagnostic investigation begins.

In cases of suspected strangulating lipoma, administering drugs that stop the peristaltic activity (gut motility) in the intestines can reduce the amount of intestine trapped in the peduncle and improve outcomes. [2]

In addition to a physical exam and medical history, diagnostic tools to identify a strangulating lipoma include: [3][4][5][6][7]

  • Abdominal ultrasound
  • Rectal palpation
  • Abdominocentesis (sampling liquid from the abdomen for testing)
  • Blood work
  • Urinalysis
  • Fecal analysis
  • Dental investigation
  • Intestinal biopsies
  • Surgical exploration of the abdomen (laparotomy/celiotomy)
  • Endoscopy

Treatment

In horses with strangulating lipomas, early detection and referral to a veterinarian provide the best chance of survival. [2]

Treatment of strangulating lipoma is surgical. [2] In mild cases that are caught early, particularly with minimal intestinal swelling and if the strangulation occurs in an easily accessible part of the abdomen, the intestine can be unwound from the lipoma, reversing the strangulation. [2] In other cases, cutting the stalk and freeing the intestine is necessary. [2]

In more severe cases where strangulation has caused tissue death, the dead portion of the intestine must be removed, and the two healthy ends reconnected to each other. [8] If several loops of intestine are involved, more than one segment of intestine must be removed. [8]

As surgical correction becomes more invasive (i.e. more pieces of intestine need to be removed to resolve the strangulation), it is less likely the horse will be able to make a full recovery. [8]

Treatment also may include: [6][7]

Prognosis

Horses recovering from surgery usually require hospitalization and stall rest with a belly band on to protect the incision. Supportive care and monitoring are ongoing during the hospital stay. [10]

The prognosis for horses with strangulating lipomas is poor, with a reported long term survival rate of 38%. [5] Horses where the strangulating lipoma has caused sepsis or endotoxemia and those that require the removal of parts of the intestine have particularly poor prognosis. [9]

In mild cases where strangulation has not caused tissue death, prognosis is somewhat better. [2]

Complications

In some cases, the strangulating lipoma is deep in the abdomen and must be severed blindly. [2] This can cause injury to the mesentery and its blood supply vessels. [2] If the mesentery is severely injured, it may be irreparable and humane euthanasia is the only possible resolution.

Horses that survive surgery for strangulating lipomas are at risk of complications such as: [6][9]

  • Adhesions; gastrointestinal tract tissue becomes attached to the abdominal cavity, which can be painful and severely impair function
  • Intestinal rupture
  • Tissue death
  • Blood clots
  • Laminitis
  • Excess fluid in the body (edema)
  • Endotoxic shock

In some cases, horses that have strangulating lipomas removed survive but eventually develop new lipomas. [9]

Prevention

Since the exact cause of lipomas and development of peduncles is not fully understood, there are no known preventative measures to avoid strangulating lipomas at this time.

Keeping up to date with best routine wellness and management practices provides the best chance of early detection, which may improve outcomes should a strangulating lipoma develop. Strategies include:

Summary

Strangulating lipomas in horses are non-cancerous fat tumors that hang from a tether of tissue within the abdominal cavity. They develop in the mesentery and trap other structures of the digestive system causing the disruption of blood supply.

  • The underlying cause of lipomas is unknown but strangulating lipomas occur more commonly in older horses, geldings, and certain breeds
  • The risk of a lipoma becoming a strangulation is variable
  • Internal injury from a strangulating lipoma is usually life threatening; horses that survive often have permanent intestinal damage
  • Diagnostic tools include rectal palpation, ultrasound, abdominocentesis, urinalysis, fecal analysis, bloodwork, and exploratory surgery.
  • Treatment is surgical and also includes antibiotics, NSAIDs, and IV fluids.
  • Prognosis in cases that require surgery is poor
  • There are no known causes or preventative measures

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References

  1. Kilcoyne, I. & Nieto, J., Perplexing Pedunculated Lipomas. Equine Veterinary Education. 2020.
  2. Gandini, M. et al., Hypothesis on the Pathophysiology of Small Intestinal Strangulation by a Pedunculated Lipoma. Equine Veterinary Education. 2022.
  3. Bauck, A. G. et al., Mesenteric Strangulation by Pedunculated Lipomas without Involvement of Associated Intestine in Four Horses. Equine Veterinary Education. 2020.
  4. Elane, G. et al., Strangulation of the Caecum by a Pedunculated Lipoma in a Rocky Mountain Horse Gelding. Equine Veterinary Education. 2024.
  5. Edwards, G. B. & Proudman, C. J., An Analysis of 75 Cases of Intestinal Obstruction Caused by Pedunculated Lipomas. Equine Veterinary Journal. 1994.View Summary
  6. Lavoie, J.-P., Ed., Blackwell’s Five-Minute Veterinary Consult: Equine. Third edition. Wiley-Blackwell, Hoboken, NJ. 2019.
  7. Verwilghen, D. et al., A Giant Nonstrangulating Mesenteric Lipoma as a Cause of Recurrent Colic in a Horse. Equine Veterinary Education. 2013.
  8. Reed, S. M. et al., Equine Internal Medicine, 3rd ed. St. Louis, Mo: Saunders Elsevier. 2010.
  9. Rudnick, M. J. et al., Effects of Age Disease and Anastomosis on Short‐ and Long‐term Survival after Surgical Correction of Small Intestinal Strangulating Diseases in 89 Horses. Equine Veterinary Journal. 2022.View Summary
  10. Findley. J. and Archer. D., Management of the Surgical Equine Colic Patient Following Hospital Discharge. In Practice. 2014.