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Cecum and Large Intestine |  |
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Impaction: |
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The most common sites of impaction are the pelvic flexure region of the left colon, the junction of the right dorsal colon with the transverse colon, and the base and body of the cecum. The pelvic flexure and transverse colon regions are anatomically predisposed to obstruction because of the dramatic changes in size. The underlying reason for impaction of the cecum is unknown, although it has been speculated that cecal muscular activity is
abnormal in affected horses. Other predisposing factors include feed that is too coarse, diseased or poorly managed teeth, and insufficient water intake. In one clinical study, Morgan, Arabian, and Appaloosa breeds were over-represented among horses with cecal impaction, and it has been proposed that the condition may develop secondary to infection with the tapeworm
Anoplocephala
perfoliata
. Impactions also may develop secondary to other intestinal diseases and may be associated with prolonged hospitalization. Consequently, the fecal output of horses being treated for other abnormalities should be assessed on a routine basis. This is especially important in horses receiving NSAID on a daily basis. |
| Horses with simple impactions of the cecum or large colon exhibit mild intermittent signs of colic, and there is minimal evidence of systemic deterioration unless the impaction has a prolonged course. Generally, the heart rate is only slightly increased. Intestinal sounds are usually heard on auscultation of the abdomen and may be associated with the onset of pain as the affected portion of the intestine contracts against the obstruction. Diagnosis is made on rectal
examination. Although the most common site of obstruction is considered to be the pelvic flexure region of the large colon, the impacted ingesta actually fills much or all of the left ventral colon. The impacted mass may be felt extending cranially in the abdomen, and the affected segment of bowel identified by palpating the longitudinal bands on the surface of the ventral colon. Impaction of the cecum is relatively easy to identify because the mass is situated in the right
paralumbar region. The cecum can be definitively identified by palpating the taut ventral cecal band and the fat and blood vessels overlying the medial cecal band. Peritoneal fluid analysis may be normal, or the total protein concentration may be increased as the course becomes more prolonged. |
| Cecal impactions tend to be a primary cause of colic in horses >8 yr old. Alternatively, impactions may be seen in horses hospitalized for other reasons and are often associated with abrupt rupture of the cecum in these cases. Consequently, there is some controversy regarding the best method of treatment. Because medical therapy in some clinical studies has been unsuccessful in 50% of the cases, surgical removal of the impacting mass followed by an ileocolostomy has been
strongly recommended. Other veterinarians report good results with aggressive medical therapy, particularly if abdominal pain associated with the cecal impaction was the primary reason the horse required veterinary attention. |
| Medical treatment of horses with cecal or large-colon impaction involves the administration of analgesics as necessary, large volumes of balanced IV fluids, and intragastric administration of either mineral oil or dioctyl sodium sulfosuccinate and water. Feed should be restricted until the impaction is relieved. Many veterinarians consider aggressive fluid therapy to be the mainstay of treatment. Balanced electrolyte solutions are administered to induce movement of fluid from
the plasma into the lumen of the intestine. This form of treatment may require administration of >50 L of fluid/day to a 450-kg horse until the impaction is resolved. Recently, interest has increased in using enteral fluid therapy to treat horses with impactions, primarily because enteral fluid therapy is significantly less expensive than IV fluid therapy. The clinical results with enteral fluid therapy have been rewarding, and the results of experimental work in healthy
horses have shown that enteral fluid therapy is more effective than IV fluid therapy in promoting hydration of colonic contents. |
| If the large-colon impaction fails to resolve with medical management, surgery can be performed. Generally, the impaction is approached via a ventral midline celiotomy, with the affected portion of the colon gently exteriorized and positioned on a sterile colon tray. An enterotomy then is made in the pelvic flexure and the contents of the colon removed. |
| Surgery for treatment of cecal impactions requires general anesthesia, a ventral midline celiotomy, isolation of the cecum from the celiotomy site, and removal of the contents of the cecum via an enterotomy. Because impactions have recurred after simple evacuation, the cecum is bypassed with an ileocolostomy. |
| The prognosis associated with impactions involving the large colon is excellent, with a survival rate of >95%. In contrast, the survival rate associated with cecal impactions remains 50-55%, which may reflect the poor prognosis associated with cecal impactions that develop in hospitalized horses. |
| In some geographic areas, the offending material may be sand, especially if there is an insufficient amount of pasture grass and the horses are fed on the ground. The sand accumulates in the right dorsal colon and transverse colon. Intermittent signs of abdominal pain may occur due to the weight of the sand in the intestine. More severe signs of pain occur when the impaction occludes the lumen of the transverse colon. Under such circumstances, the colon proximal to the
obstruction distends with gas, and the horse may become extremely painful. It may not be possible to distinguish this condition from an intestinal displacement or volvulus. Sand also may be identified in the feces by mixing fecal material with water in a plastic rectal examination sleeve. |
| Treatment of sand impaction may be either medical or surgical. Medical treatment generally involves intragastric administration of psyllium (400 g/500 kg body wt, daily for 7 days) to purge the sand from the lumen. The psyllium flakes are added to 7.5 L of warm water and rapidly pumped into the stomach. These treatments are accompanied by analgesics as needed and IV fluids to promote movement of fluid into the intestinal lumen. |
| Surgery via a ventral midline celiotomy is necessary if the sand completely obstructs the lumen of the transverse colon. The left colon is exteriorized on a sterile colon tray, and the sand is removed via an enterotomy. The prognosis is usually good. Problems sometimes develop during surgery if the colon was damaged due to the extensive weight of the sand or while the sand is being removed from the intestine. See also
Sand Enterocolopathy. |
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Enterolithiasis: |
| Enteroliths are concretions composed of magnesium ammonium phosphate crystals around a nidus (eg, wire, stone, nail). Enteroliths may be seen singly or in groups and are commonly found in horses in certain parts of the USA, including California, the southwest, Indiana, and Florida. Enterolithiasis commonly affects Arabian horses, but the fact that these horses are extremely popular in the aforementioned areas confounds the question regarding breed association. Most horses with
enteroliths are ~10 yr old; enterolithiasis rarely is seen in horses <4 yr old. Although not all factors that contribute to the formation of enteroliths have been identified, the results of recent clinical studies indicate that large colon contents from horses with enteroliths have higher mineral (magnesium, calcium, and phosphorus) concentrations and pH than contents from horses with colic not due to enteroliths. A common factor associated with enterolithiasis is the
consumption of alfalfa hay, which results in a higher pH and increased concentrations of calcium, magnesium, and sulfur in the large colon. |
| Many horses with enterolithiasis have a history of recurring colic, presumably indicating that the enterolith(s) had caused partial or temporary obstruction of the colonic lumen. If the enterolith becomes lodged at the origin of the transverse colon, the colon proximal to the obstruction distends with gas and the pain is severe. Distention of the abdomen may be marked. Heart and respiratory rates are increased, and the mucous membranes may be pale or pink. Generally, colonic
and cecal distention is evident on rectal examination, but the mass rarely is palpable because the transverse colon is cranial to the cranial mesenteric artery. Analysis of the peritoneal fluid is usually within normal limits unless ischemia of the colonic wall has developed over the enterolith. In areas where the problem is endemic, radiography may be used to identify the enteroliths. |
| Treatment involves surgery via a ventral midline celiotomy to decompress the colon and cecum and then to remove the stone(s). The left portion of the large colon is exteriorized and positioned on a sterile colon tray, the ingesta removed via an enterotomy, and then the enterolith(s) removed. If the stone has a flat side or a polyhedral shape, the rest of the large and small colons must be thoroughly checked for other stones. The prognosis is excellent, with practices in endemic
areas reporting survival rates of 95%. |
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Left Dorsal Displacement: |
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Left dorsal displacement of the colon is seen when either the pelvic flexure or the entire left colon becomes displaced over the renosplenic ligament. Because the renosplenic ligament is not attached to the most dorsal aspect of the spleen, a natural cleft exists between the spleen and left kidney. Although all ages and sexes of horses are affected equally, results of a clinical study indicate that the displacement is common in young horses. |
| Because left dorsal displacement results in simple obstruction of the colon at the point where it hangs across the ligament, the condition usually is associated with moderate abdominal pain or a prolonged course of intermittent painful episodes. The mucous membranes remain normal, and the heart rate is increased only slightly. The diagnosis usually is made on rectal examination (palpating the pelvic flexure over the ligament, palpating the bands of the left ventral colon
running dorsocranially to the left kidney, and detecting that the spleen is displaced toward the middle of the abdomen). The condition also may be identified using ultrasonography. A paracentesis may yield blood if the spleen is displaced toward the midline. |
| Four forms of treatment have been used: 1) withholding feed to determine whether evacuation of the intestinal contents will allow the colon to return to its normal position, 2) rolling the horse to dislodge the colon from the ligament, 3) administering phenylephrine and/or jogging the horse to cause splenic contraction and correction of the displacement, or 4) performing surgery to return the colon to its correct position. The rolling procedure involves short-term anesthesia
(generally xylazine or detomidine and ketamine), elevation of the horse’s hindlimbs, and rolling the horse 360°. Surgery is performed via a ventral midline celiotomy. The advantage of surgery is that the viability of the colon can be assessed. Overall, the prognosis is good, with most studies reporting survival rates >80%. |
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Right Dorsal Displacement: |
| The left colons move laterally around the base of the cecum to lie between the cecum and the right body wall. With the most common form of this displacement, the pelvic flexure ends up positioned near the diaphragm. In many instances, the displacement may be complicated by twisting of the colon near the base of the cecum. Although there may be some interference with venous drainage from the affected colon, usually the arterial supply remains intact.
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| Most horses with right dorsal displacements exhibit moderate degrees of pain, and there is slow development of systemic deterioration. In some cases, however, the pain may be severe. Rectal examination may reveal the taenia of the colon running transversely across the pelvic inlet. It may not be possible to palpate the ventral cecal band on rectal examination. Some horses with this condition have gastric reflux, presumably due to occlusion of the lumen of the duodenum. |
| Some horses with this condition appear to be stable and may show intermittent signs consistent with mild abdominal pain. Treatment may be conservative, involving attention to fluid needs and administration of mild analgesics. For painful horses, however, surgery must be performed to locate the pelvic flexure, to exteriorize and decompress the left portion of the colon, if possible, and then to relocate the colon to its normal position by rotating it around the cecal base. The
twisting of the colon must be identified and corrected. The prognosis for survival is good, provided that the colonic wall is not damaged during surgery. |
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Right Dorsal Colitis: |
| Right dorsal colitis has been recognized with increasing regularity in the past decade, particularly in, but not limited to, horses receiving excessive amounts of NSAID. Because the condition has been identified in horses receiving recommended doses of these drugs, it appears that some horses are particularly sensitive to their toxic effects. The drug most commonly associated with right dorsal colitis is phenylbutazone, but this may reflect the common and often chronic use of
this drug. The most common lesions reported in horses with right dorsal colitis are ulceration and thickening and/or fibrosis of the wall of the right dorsal colon. |
| Horses commonly present with abdominal pain, anorexia, and lethargy. In many cases, the signs are consistent with severe abdominal pain, fever, endotoxemia, and diarrhea. Horses with the more chronic form of the disease present with intermittent abdominal pain, weight loss, lethargy, and anorexia. In most cases, hypoproteinemia is a common finding on hematology, and may account for ventral edema in some horses with the chronic form of the disease. The diagnosis is usually based
on the history, clinical signs, and hematologic findings. In some cases, ultrasonographic evaluation of the colon via the twelfth to fifteenth intercostal spaces may provide evidence of marked thickening of the colonic wall. |
| Treatment of affected horses includes discontinuation of NSAID, rest, and a change in diet to a complete pelleted feed that contains ≥30% dietary fiber. Some clinicians recommend the feeding of many small meals daily, many recommend the inclusion of psyllium to promote mucosal healing, and some administer sucralfate or metronidazole. Horses with uncontrollable pain may require surgery to resect or bypass the affected portion of the right dorsal colon. The prognosis for horses
with right dorsal colitis is guarded. |
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Volvulus of the Large Colon: |
| Although the term “torsion” has been used for years to indicate that the colon has twisted on itself, the involvement of the mesentery between the ventral and dorsal colons indicates that the condition is a volvulus. When viewed from the most common site of the volvulus (the junction between the right ventral colon and the cecum), the volvulus most often occurs in a clockwise direction; the cecum may or may not be involved. If the volvulus is <270°, there may be obstruction
of the bowel lumen without ischemia. If the volvulus is >360°, there is strangulating obstruction of the entire left colon.
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| The onset of colic is sudden, and the degree of pain may be mild to moderate if the volvulus results only in obstruction of the intestinal lumen. When the twist is more extensive, the pain is severe and the horse may fail to respond to analgesics. The colon is extremely enlarged, and the mesentery between the dorsal and ventral colons is edematous on rectal examination. The heart rate is rapid, the horse’s condition deteriorates rapidly, and there is poor peripheral perfusion.
Distention of the abdomen usually is marked. Generally, results of peritoneal fluid analysis and the degree of colonic involvement are poorly correlated. |
| Although the cause of colonic volvulus remains unknown, it is presumed to be associated with a disproportionate amount of gas in the colon. On broodmare farms, the condition frequently is associated with recent (within 90 days) or impending parturition, a grass diet, or highly fermentable feeds. The presence of a foal at the mare’s side (recent history of parturition) is an additional risk factor. |
| Treatment of colonic volvulus requires surgery to correct the volvulus and remove affected bowel, if necessary. Although the technique for removal of 90% of the colon has been perfected in healthy horses, extreme difficulty can be encountered if the colon is edematous. Because the recurrence rate has been estimated to be as high as 20% in some clinical studies, colopexy procedures have been devised to reduce the recurrence of the condition in broodmares. Although the results of
a study involving several university hospitals reported a 27% survival rate, survival rates >85% are common for practices situated near broodmare farms. |
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Impaction and Foreign Body Obstruction of the Descending Colon: |
| Abnormalities involving the descending (small) colon are infrequent, accounting for <5% of conditions characterized by colic in one study. The more common causes include meconium retention, impaction, and foreign body obstruction. Meconium retention is seen in newborn male foals within the first 24 hr of life. Affected foals swish their tails from side to side, strain to defecate, and roll. The diagnosis is made by careful digital examination. Treatment involves gentle
administration of a warm, soapy water enema. The prognosis is excellent. |
| Impaction of the descending colon is seen in ponies, miniature horses, and adult horses with limited access to drinking water or with other causes of intestinal stasis. Most recently, the condition has been associated with salmonellosis, although a cause and effect relationship has not been proved. Pain may be severe if the obstruction is complete. In such cases, tympany of the colon occurs secondarily, and ileus results. The diagnosis is made in adult horses by palpating the
obstructing mass in the ventral portion of the abdomen on rectal examination. Foreign body obstruction of the descending colon must be considered if the horse is <3 yr old; the offending material may be rubber fencing, nylon fibers from halters or lead shanks, hay net, or feed sacks. Horses with impactions may be treated medically with analgesics, IV fluids, and gentle enemas. Often, however, surgery is required to evacuate the colon due to severity of pain and gas distention.
The prognosis associated with impaction of the descending colon is fair unless it is complicated by severe colitis after the obstruction has been removed. The prognosis is good. |
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