In our last post, we discussed (mainly) non-surgical types of large intestinal colic. However, as we all know, sometimes colic goes beyond what we can treat in the field and referral for surgery is necessary. Typically, these result from the colon moving (or displacing) into a place that it shouldn’t be. That being said, some of these can be treated medically, however not always successfully. Since we’ve already gone over the anatomy of the large colon, (See Large Intestinal Colic: Part One) let’s jump right into what might have happened if your horse’s bowel becomes blocked.
Right Dorsal Displacement: The left colon is quite mobile and likes to get stuck in places. In a right dorsal displacement (RDD), the left colon slides around to the right side of the abdomen and gets stuck between the cecum and the body wall. The pelvic flexure (the U-shaped area at the top of the picture) moves from the back end of the abdomen (near the rectum) to end up near the diaphragm. This is all kinds of crazy! The large intestine becomes partially occluded and gas distended. In practice, we can see this occur in conjunction with a pelvic flexure impaction. Generally speaking, the blood supply remains intact so the bowel remains healthy. We can sometimes treat these with fluids and withholding feed, but often times surgery is required. At surgery, the colon just needs to be decompressed and repositioned into the appropriate anatomic location. As long as nothing more serious is going on, these horses recover quite well.
Left Dorsal Displacement: Again, the left half of the colon goes for a walk-about. This time, it slides up along the left body wall and gets hung up between the spleen and the kidney. Why? Well, there’s structure there called the nephrosplenic ligament – merely a tissue attachment between the spleen and the kidney. (That’s also why the other name for this type of displacement is a “nephrosplenic entrapment”.) The problem is that this ligament can act like a hammock for the large colon. And we all know how hard it is to get out of a hammock! Feed material may still be able to pass through initially, but gas buildup and the excess weight on the spleen pushes that organ out of position as well. This can be quite uncomfortable, as you can imagine. Medical therapy with phenylephrine (given slowly intravenously) can sometimes to shrink the spleen allowing the colon to “fall” off the nephrosplenic ligament (usually assisted with trotting or trailering the horse), however is not usually successful. Attempts are sometimes made to anesthetize and “roll” a horse to try to dislodge the spleen as well, but this is difficult for many reasons. Surgery is sometimes required (we estimate 50% of these colics require surgery), and again aims at merely emptying the colon and putting it back where it belongs.
Colon Torsion or Volvulus: (Above) This is one of the scariest types of large intestinal colic. Imagine a line drawn along the length of a horse through the chest and out the back end. Then we take the large colon and twist it around this line, spinning it on its axis. That is a volvulus, and while they commonly rotate clockwise, it can go in either direction. If the colon rotates >360 degrees, blood supply will be cut off and significant injury to the bowel occurs. This generally results in a poor prognosis and requires euthanasia. However, if it is less than 270 degrees rotated, the colon is usually ok and just needs to be twisted back around that rod. This is more common in broodmares post-foaling as there is a large amount of space left in the abdominal cavity after the foal is born. Surgery is required to correct a volvulus.
Cecal Impaction: In the previous post, we mentioned pelvic flexure impaction. While this is probably the most common area for an impaction, it is not the only area where an impaction can occur. The cecum is another structure that can become impacted, and medical treatment can be difficult. Initially, horses with cecal impactions have intermittent colic which can become more severe if it is prolonged in course. Surgery is often recommended to removed the impaction, especially if medical therapy is not successful. Prognosis if surgery is performed is fair, as success rates are about 70%. The success rate rises to 80% if these cases are able to be treated medically.
Enteroliths: An enterolith is a concretion that forms in the GI tract. The term broken down is entero (GI tract) and -lith (stone). It is very uncommon to see this in the Northeast where we are, but can be seen in areas such as the southwest and Florida. It’s unclear what causes these to form, it often occurs in horses with higher mineral concentrations. Feeding of alfalfa hay has been attributed to this higher mineral concentration.
The problem with enteroliths is that they can grow large enough to plug up the GI tract. Not only that, but they can abrade the lining of the intestine. Imagine if you had a boulder rolling around in your gut! Horses will typically show recurring colic signs, but can become extremely painful when the lumen of the intestine becomes blocked. Surgery is required to remove these, but prognosis tends to be quite good.
The colon is a complex structure in horses and as such causes many problems. Some of these can be treated easily on the farm, but sometimes they require referral for further care or surgery. The choice on whether or not to do surgery should be made prior to any problems occurring, as it can be an emotionally and financially draining endeavor. That being said, depending on the issue, large intestinal colic surgery does usually carry a good prognosis.
