Small Intestine Strangulation by Lipoma in Horses: New Theory

Most abdominal lipomas originate from fat plaques of the small intestinal mesentery, a fibrofatty membrane that envelopes the intestines and anchors them to the abdominal wall. Because they are benign, lipomas can lie dormant indefinitely within the abdominal cavity until their specific location or size causes a problem.

These tumors often feature a narrow stalk, or pedicle, that extends from the mesentery to the growing tumor and gives rise to their common name, pedunculated lipomas. For many years, veterinarians believed that a lipoma bobs on its pedicle until it eventually loops around the small intestine, creating a knot that strangulates the organ and ultimately inhibits the flow of ingesta. Despite this explanation, surgeons have found it difficult to confidently replicate this mechanism during surgical correction.

A team of researchers recently hypothesized an alternative theory, one that is more consistent with surgical findings. Simply put, this theory starts with a pedicle under tension by the weight of the lipoma, with the tension producing a slit-like opening or gap between the pedicle stalk and the mesentery or small intestine. Under the influence of peristalsis, the wavelike movements that move ingesta along the gastrointestinal tract, loops of intestine turn into that opening. These loops eventually become filled with ingesta. The increased weight of the loops that pass through the opening causes the pedicle to turn back on itself, forming a bind and constricting the small intestine.

Understanding how the small intestine becomes trapped by a lipoma can help veterinarians pursue better ways to surgically correct them.

Lipomas seem to be problematic in older horses, with those in their mid to late teens most often affected. Researchers have postulated that increased body weight may be a risk factor for pedunculated lipomas in horses, yet no specific statistics have been recorded.⁺

“Certainly, horses of all sizes and shapes can be diagnosed with pedunculated lipoma. While no exact link has been established between obesity and tumor formation, speculation surrounds this idea,” said Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research.

“The advantages of maintaining a horse in moderate body condition—a 5 on the body condition score chart—are numerous, including benefits to respiratory and musculoskeletal health as well as long-term metabolic well-being,” said Crandell. “Plus, from a practical perspective, feeding horses more than necessary can increase horse-keeping costs considerably.”

Crandell recognizes the difficulty in maintaining moderate body condition in the face of free-choice forage consumption. “Managing easy keepers can be difficult because, as horse owners, we want to see horses grazing contentedly. As stewards of their health, though, we must often use grazing muzzles, drylots, and other management strategies to keep life-threatening problems from cropping up.”

Widespread use of ration balancers and high-quality vitamin and mineral supplements has made it possible for horses on all-forage diets to receive the nutrients necessary for optimal health, according to Crandell.

 ^*Grandini, M., D.E. Freeman, and G. Giusto. 2022. Hypothesis on the pathophysiology of small intestinal strangulation by a pediculated lipoma. Equine Veterinary Education 34(4):207-213.

 ⁺Bilkslager, A.T., K.F. Bowman, M.L. Haven, et al. 1992. Pedunculated lipomas as a cause of intestinal obstruction in horses: 17 cases. Journal of the American Veterinary Medical Association 201:1249-1252.