Page 873 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

848 CHAPTER 4

VetBooks.ir involving the caecum, caecal trocharisation may be when viewed from behind (clockwise rotation). The
In horses with severe abdominal distension also
pathophysiology of large colon volvulus depends on
required (see Caecal tympany, p. 834 ). With severe,
uncontrollable pain, severe abdominal distension the degree of rotation of the colon. If the rotation
is <270°, the blood supply to the large colon is usu-
or progression of clinical signs, surgical interven- ally not compromised and only the colonic lumen
tion may be required to decompress the intestine is obstructed. Such large-colon rotations result in
and rule out the presence of a concurrent surgical obstruction of normal passage of gas and ingesta. If
lesion. the rotation is >270°, the lumen of the large colon is
obstructed and the blood supply (venous or arterial
Prognosis and venous) is compromised, resulting in a stran-
Most cases respond well to conservative therapy. gulating lesion. In most cases, venous occlusion
If the clinical condition deteriorates or there is a and haemorrhagic strangulating obstruction occur.
poor response to treatment, the horse should be This results in sequestration of blood in the stran-
re- evaluated to ensure that another problem is not gulated portions of the colon and ischaemic lesions
present. It is possible that large-colon displacement of the mucosa. The latter dies off within a few hours
or volvulus could occur secondary to gaseous dis- of ischaemia and intraluminal leakage of plasmatic
tension of the large colon. Management should be fluids and absorption of endotoxin occur. Affected
reviewed to identify and address any risk factors that horses rapidly develop both hypovolaemic and endo-
might be present. toxaemic shock.

COLONIC VOLVULUS Clinical presentation
Clinical signs of colonic volvulus vary with the
Definition/overview degree of colonic rotation. Horses with non-
Large-colon volvulus is a relatively common cause of strangulated large-colon volvulus (rotation <270°)
severe, life-threatening colic. Both non-strangulated display clinical signs similar to those associated
and strangulated volvulus may occur, with the lat- with large-colon impaction or non-strangulating
ter being more frequent. Strangulated large-colon displacements. Horses with strangulated large-
volvulus rapidly induces hypovolaemic and endo- colon volvulus experience peracute colic and
toxaemic shock and affected horses require emer- severe, intractable abdominal pain as the most
gency surgical treatment. The prognosis for survival common clinical findings. Moderate to severe
for horses with strangulated large-colon volvulus is abdominal distension causing respiratory compro-
guarded to poor. mise is also frequently observed. Signs of toxaemia
and cardiovascular compromise may be present
Aetiology/pathophysiology and can be severe.
The precise cause of large-colon volvulus in horses
is not currently known, but broodmares just before Differential diagnosis
or after parturition appear to be at increased risk Differential diagnoses for non-strangulated large-
for this condition. Changes in digestion and/or vis- colon volvulus include large-colon impaction and
ceral positioning during pregnancy may predispose large-colon displacement such as right and left dor-
mares to large-colon volvulus. The condition is not sal displacement. Strangulated large-colon volvu-
restricted to broodmares and any changes in large- lus is probably the condition that induces the most
colon motility may predispose horses to the develop- acute and violent signs of colic in horses. The only
ment of large-colon volvulus. other conditions that can induce such signs are
The equine large colon has only two fixed attach- incarcerated internal hernia (diaphragmatic hernia,
ment points: the caecocolic ligament and the trans- epiploic foramen entrapment, incarceration in the
verse colon. In most cases of large-colon volvulus, gastrosplenic ligament and strangulated inguinal
the right ventral colon displaces dorsomedially hernia).