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Pedunculated lipomas in horses

Pedunculated lipomas are benign tumors that most frequently arise from the mesentery of the small intestine and remain attached by a pedicle. Obstruction of intestine by a pedunculated lipoma is one of the more commonly encountered causes of colic requiring surgical management. Geldings and ponies are know to be at a greater risk of colic resulting from pedunculated lipomas than are other horses. Upon review of the records of 17 horses that were evaluated and treated because of colic caused by pedunculated lipomas between 1983 and 1990, the mean age of the horses was determined to be 16.6 + 3.9 years. Most obstructions are closed loop strangulating obstructions resulting from the pedicle becoming wrapped around a length of intestine and the lipoma tucking itself underneath this band. The resulting tight compression occludes the lumen of the intestine and corresponding mesenteric vessels. At laparotomy, the strangulated loop of bowel frequently shows advanced infarction appearing reddish-black with very thin walls, suggesting that arterial occlusion may occur very soon after initiation of the obstruction. In contrast, in horses with non-strangulating obstruction, the lipomas are frequently large and the pedicle is drawn firmly across the intestine by the weight of the lipoma resulting in obstruction without vascular impairment. Alternatively, having encircled the gut, the lipoma may become enveloped in the mesentery.

Pedunculated lipomas start as localized plaques of fat between the two serosal layers of mesentery. As these aggregations enlarge, the overlying serosa stretches forming a pedicle, which lengthens as the weight of the lipoma increases. While many old horses and ponies have one or more lipomas attached to mesentery, only a small proportion of these animals develop strangulating obstruction. How the lipoma becomes intricately wrapped around a loop of intestine, which may be several meters long, is unknown. The weight of the lipoma, the length of the pedicle and sufficient momentum resulting from movement of the horse or intestinal motility would seem likely contributory factors in this bizarre accidental obstruction of small intestine and, much less commonly, small colon. Only one report of strangulation of the small colon has appeared in the literature. The paper describes the extensive resection and anastomosis of the descending colon of a horse after strangulation by the pedicle of a mesenteric lipoma originating from the mesocolon.

Gastric reflux is a common clinical finding in cases of small intestinal obstruction associated with ileus and buildup of fluid anterior to the obstruction. Deboom (1975) suggests that this reflux may result from compression of the proximal duodenum by the gradual distention of the large intestine through the proximity of the attachment of these two structures, or perhaps from the effects of severe pain leading to a generalized ileus. Some reports suggest that horses with descending colon obstruction often present with mild changes and, as time progresses, there is a slow deterioration of clinical signs, and hematological and peritoneal fluid values associated with buildup of fluid and gas anterior to the obstruction.

Treatment of a strangulating lipoma involves resection of the lipoma at the base of its pedicle and resection of any compromised intestine. The decision on whether to resect, and how much to resect, is a judgement made for each individual case. Evaluation of the color of the serosa and mesentery, reflex motility, a pulse in the mesenteric vessels and evaluation of the mucosa via enterotomy are the most frequently used criteria. The incidence of complications following resection and anastomosis of the affected intestine appears to be high. Contamination is difficult to control because of high intraluminal bacterial count and particulate matter within the lumen.

Various postoperative treatment regimes have been recommended to minimize complications at surgery. A combination of antimicrobials to provide broad spectrum activity is recommended. Ideally, food should be withheld for a minimum of 24 hours, then re-introduced slowly to minimize the bulk of feed passing through the surgical site and combined with fecal softeners to reduce tension on the anastomosis. Aggressive peritoneal lavage, with heparin added to the lavage solution, frequent walking, anti-inflammatory medications, and motility stimulants may be used to minimize formation of abdominal adhesions.

The clinical signs associated with pedunculated lipomas depend on the segment and extent of intestine involved and the degree of strangulation. Horses often present with mild to moderate abdominal pain and may initially respond well to analgesic medication. The majority of horses with obstructing lipomas have palpable small intestinal distention on rectal examination. Fluid obtained by abdominocentesis may be normal early in the course of the obstruction; however, most horses with strangulating lipomas have increases in peritoneal fluid total protein and WBC counts. Lipomas are also usually discovered as incidental findings at surgery or necropsy.

The short-term survival rate for strangulating pedunculated lipoma obstruction cases alone is 43%. This may be due to a reluctance to refer older animals with colic, leading to a greater delay between the onset of obstruction and surgical correction. Endotoxemia and post-operative ileus are frequent causes of mortality in cases of strangulating obstruction. Long term survival rate is known to be 38%, indicating an appreciable mortality rate due to colic in the first year after surgery. Adhesions, mesenteric stump abscesses or stenosis of the anastomosis are all possible strangulations.

-by Saeed Bashir, ECFVG Student
-edited by Dr. Kaori Sakamoto, ADDL
Graduate Student

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Vol. 68.
2. Equine Veterinary Journal: 1994. 26:18.
3. Equine Veterinary Journal:1978. 10;269
4. Equine Veterinary Journal: 1994. 26:20
5. Kunesh JP: 1984. JAVMA 185:1222
6. JAVMA: 1992. Vol 201
7. Stashak TS: 1982. Vet Clin North Am.p. 147





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