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
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