Page 878 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.2 The lower gastrointestinal tr act 853

VetBooks.ir LARGE-COLON IMPACTION 4.170

Definition/overview
Impaction of the large colon with ingesta is a com-
mon cause of colic.

Aetiology/pathophysiology
Large-colon impactions occur from accumulation
of dehydrated and densely packed ingesta, often at a
site where the large colon narrows, such as the pelvic
flexure or right dorsal colon (Fig. 4.170). The most
common site is the pelvic flexure although right dor-
sal impactions are not uncommon.
Factors affecting hydration of the colonic con- Fig. 4.170 Severe impaction of the right dorsal colon
tents and intestinal motility may predispose to the that required surgical intervention.
development of impactions. These include ingestion
of highly fibrous grass or hay, poor diet, decreased
water intake (restricted access, excessively cold water, peritonitis, exertional rhabdomyolysis, urinary
change in water source), management changes, obstruction and reproductive tract lesions should
transportation, sudden exercise restriction, pain, also be considered.
sand enteropathy and EGUS. Many cases occur in
the absence of these factors. As firm ingesta accu- Diagnosis
mulates in the affected area, colonic distension from Most impactions of the large colon are palpable p/r
ingesta and altered movement of intestinal gas cause by identification of a section of ingesta-filled and
variable signs of pain. distended large colon. Pelvic flexure impactions
are the most obvious and they sometimes extend
Clinical presentation into the pelvic canal. The size and texture of the
Non-specific signs of abdominal pain, including impaction should be noted. Occasionally, an impac-
anorexia, flank-watching, pawing, rolling, tail- tion may lie beyond reach of the examiner. Gastric
swishing, straining to defaecate and sweating, are reflux is unusual with large-colon impactions, but it
commonly observed. Intermittent pain over a few can occur, presumably as a result of small-intestinal
days may be reported. Pain can range from mild and compression by the distended large colon or pain-
intermittent to severe and continuous. Heart rate induced ileus. Transabdominal ultrasonography
will be correspondingly elevated. Borborygmi are can be useful in horses that are too small for p/r
often decreased. Signs of systemic compromise or palpation.
toxaemia should not be evident. Intestinal tympany Peritoneal fluid is normal in the vast majority of
may be present. Sometimes, a decrease in faecal pro- impactions. If abdominocentesis is performed, care
duction or passage of firm, dry faeces is reported. should be taken to avoid penetrating a markedly dis-
Faeces may be covered in mucus, indicating delayed tended, friable large colon. Abdominocentesis should
intestinal transit. Dehydration may be present, be performed in horses that deteriorate acutely in
depending on the duration of signs. order to determine whether colonic rupture may
have occurred.
Differential diagnosis
Other causes of mild to moderate colic without Management
intestinal compromise should be considered. These Feed should be withheld and can be restricted
include spasmodic colic, intestinal tympany, sand from otherwise healthy adult horses for a week
impaction, enteroliths and large-colon displacement. without adverse consequences in most cases. Care
Extraintestinal diseases such as laminitis, pleuritis, should be taken in obese animals to avoid inducing