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Surgical Options and Prognosis for the Acute Abdomen: Large Intestine
T. Mair
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Take Home Message
The most important surgical diseases of the large intestine include non-strangulating colonic displacements (left dorsal displacement, right dorsal displacement, non-strangulating volvulus) and colon volvulus/torsion. In some parts of the world, enterolithiasis is also common. Horses that are successfully treated for displacements or volvulus are at a significant risk of recurrence.
Introduction
The large colon in an adult horse is approximately 3.4 meters in length and has a capacity of approximately 81 L. The large size and mobility due to sparse mesenteric attachments of the ascending colon predispose it to a variety of displacements. The colon is normally looped back upon itself at the pelvic flexure and then folded at the sternal and diaphragmatic flexures to fit within the abdomen. Colonic mobility is restricted only by attachments to the cecum and transverse colon. In addition to this anatomical predisposition, other risk factors for various displacements include age (> 7 years), large stature (Warmbloods), foaling and lactation, abrupt feeding changes and previous displacement.
Non-Strangulated Colonic Displacement
In these disorders, the colon moves out of its normal position and becomes sufficiently entrapped, kinked, or twisted to obstruct the flow of gas and ingesta. The vascular integrity of the affected colon remains normal or is minimally affected. The clinical picture is that of simple obstruction of the large intestine and must be differentiated from impaction, enterolithiasis, and other colonic disorders inducing simple obstruction. Obstruction due to displacement may be either complete or partial (blocking ingesta but permitting passage of gas) thus further confounding the diagnosis. A variety of colonic malpositions may result in non-strangulated displacement but there are three common types:
- left dorsal displacement of the colon (renosplenic ligament entrapment)
- right dorsal displacement of the colon
- non-strangulated volvulus of the large colon
Left Dorsal Displacement of the Colon (Renosplenic Ligament Entrapment)
Entrapment of the left colon over the renosplenic ligament (nephrosplenic ligament or suspensory ligament of the spleen) results in partial or complete colonic obstruction. Strangulation of the entrapped colon is rare.
The clinical signs of left dorsal displacement of the colon are variable depending on the length of colon involved, the degree of tympany and the amount of traction on the renosplenic ligament. In mild cases, gas accumulation proximal to the obstruction is minimal and affected horses present with only low grade pain. In severe cases with marked tympany of the large colon (and cecum), the signs include marked, unrelenting pain, tachycardia, and abdominal distension. Some horses have substantial nasogastric reflux. Rectal findings include left colon tympany coupled with convergence of left colon tenia dorsally over the renosplenic ligament. Additional findings may include difficulty in palpating the dorsal border of the spleen, ventral displacement of the spleen, and variable cecal tympany. Ultrasonographic findings of a gas-filled viscus axial to the splenic base or obliterating the dorsal border of the spleen/left kidney are typical.
Treatment options include the following:
- Conservative therapy - food restriction and analgesia.
- Phenylephrine (3 to 6 µg/kg/min for 15 minutes) + exercise. Phenylephrine results in splenic contraction. During administration, horses should be monitored for reflex bradycardia, and administration should be discontinued if severe bradycardia occurs.
- Rolling under general anesthesia. Phenylephrine can be administered immediately before anesthetizing the horse. The anesthetized horse is placed in right lateral recumbency, then rolled onto its back (at which time it is jostled to try to encourage the colon to come out of the nephrosplenic space) and then into left lateral recumbency.
- Surgical treatment
If pain and distension are not severe, medical management is frequently successful, but in horses with severe pain or that are unresponsive to medical treatment, surgery is often required.
Horses successfully treated for left dorsal displacement of the colon are at increased risk of one or more recurrences. Obliteration of the renosplenic space has been successfully used to prevent recurrences of the condition.
Right Dorsal Displacement of the Colon
Displacement of the large colon between the cecum and right body wall results in signs of colic due to obstruction. The cause of this problem is unknown. Most commonly the pelvic flexure and left colon pass in a cranio-caudal direction between cecum and right body wall. These structures then turn cranial placing the pelvic flexure in the cranial abdomen. Less commonly, the pelvic flexure and left colon pass caudocranial between the caecum and body wall, also with the pelvic flexure in the cranial abdomen. Either type may be accompanied by 180°–360° volvulus of the large colon. The clinical signs of right dorsal displacement of the colon are extremely variable ranging from a prolonged course of very mild colic to an acute episode of severe pain and tympany. Rectal examination reveals large colon segments with variable tympany passing from between the cecum and right body wall, behind the cecum and then forward. The pelvic flexure ordinarily is not palpable. In cases accompanied by 270° or greater volvulus, edema in the wall of the colon may be evident during rectal palpation. This finding may be confirmed ultrasonographically. [...]
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