Small Intestine Volvulus - Horse
A small intestinal (SI) volvulus occurs in the horse when the intestine rotates on its mesenteric axis through an angle greater than 180o, resulting in strangulation. The pathogenesis is thought to be due to a segment of hypermotile intestine preceding a segment where peristalsis has ceased, leading to the development of a twist. Volvulus may occur as a primary cause of colic or secondarily as a result of another condition such as a lipoma, incarceration within the mesentery or adhesion within the abdomen.
SI volvulus has been reported to be more common in horses less than three years of age, and to be particularly prevalent in foals aged two to four months. This has been hypothesised to be due to a change in diet from milk to solid food at this age.
The clinical signs associated with this condition are both acute and severe. Common signs include:
- Severe, unrelenting abdominal pain that is non-responsive to analgesia
- Reduced or absent borborygmi
In addition to the above signs, signs relating to endotoxaemia may be present including prolonged capillary refill time, congested mucous membranes and poor pulse quality. Abdominal distension may be observed, especially in cases where the mesenteric root is involved.
Diagnosis is made based on the above clinical signs and a number of confirmatory tests. Large volumes of nasogastric reflux may be obtained; greater than 2L of fluid with a pH greater than 5 is considered abnormal. Rectal examination may indicate multiple distended loops of small intestine, a finding that usually indicates the need for surgical intervention. Ultrasonographic examination often reveals a distended, oedematous, fluid-filled small intestine proximal to the strangulated segment. The intestinal wall is hypoechoic and peristalsis may be absent. PCV and total protein are increased with a concurrent increase in respiratory rate to compensate for metabolic acidosis. Abdominocentesis may initially yield a mildly serosanguineous fluid; as strangulation continues, the fluid becomes turbulent with a large increase in white blood cells and protein.
Also see Colic Diagnosis in Horses.
Treatment for this condition is surgical and consists of correction of the volvulus via a ventral midline coeliotomy. This must be performed within hours of the vovlulus occurring due to the significant cardiovascular deterioration associated with the condition. Following reduction of the volvulus, nonviable bowel is resected and an end-to-end anastamosis is performed.
Also see Medical Treatment of Colic in Horses.
The prognosis associated with small intestinal volvulus is poor due to the rapid cardiovascular deterioration associated with the condition. Previous authors have reported that euthanasia should be considered if greater than 50% of the small intestine requires resecting.
McIlwraith, C. W., Robertson, J. T. (1998) McIlwraith & Turner's Equine Surgery: advanced techniques Wiley-Blackwell
Stephen, J. O., Corley, K. T. T., Johnstone, J. K., Pfeiffer, D. K. (2004) Small Intestinal Volvulus in 115 Horses: 1988-2000 Veterinary Surgery 33:333-339
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