Megacolon in the Cat

The colon is a tubular, muscular structure, which represents the termination of the intestinal tract.  It is continuous with the rectum.  The colon has several functions, such as absorption of water, storage of feces, and defecation (emptying of the bowel).  When the muscles in the wall of the colon are stimulated to contract by nerves from the spinal cord, fecal material is pushed out of the body.  

Megacolon is a condition of colonic dilation and is a fairly common problem in the cat.

Contributing Factors

Any condition that slows movement of material through the colon or causes an obstruction in the colon may lead to constipation.  Chronic constipation can lead to development of Megacolon.  Some possible causes would include refusal to use a soiled litter box, impaction with hair or foreign material, injury to the spinal cord, intestinal cancer, intestinal strictures, and dehydration.

Prevalence

Megacolon generally occurs in middle-aged to older cats, but has also been seen in cats only 3-4 years old.  Some investigators feel that it occurs more commonly in male cats than in females.  It occurs in both purebred and non-purebred cats.

Causes/Transmission

If the nerves to the colon do not function properly, the muscles of the colonic wall will not contract properly.  Eventually, these muscles stretch and the colon begins to enlarge.  When fecal material accumulates and is not moved out of the body, severe constipation results.  With time, the colon can become 3-4 times larger than in the normal cat.

As noted above, an injury to the spinal cord can result in development of megacolon.  Also, mechanical obstruction caused by tumor, foreign bodies, hairballs, and strictures can lead to megacolon.  However, in most cases, we can not determine the reason that the nerves to the colon quit functioning so it is termed “idiopathic.”

Clinical Signs

Many cats with megacolon appear relatively healthy and have no signs other than chronic constipation.  When other signs are present, these include a distended abdomen, anorexia, weight loss, vomiting, nausea, and straining to defecate.  In severe cases, the rectum may protrude from constant straining.

Diagnosis

In many cases, the history given by the owner is suggestive of megacolon and it can be confirmed by palpation of the abdomen or examination of the rectum.  It can be helpful to take an abdominal x-ray to determine the extent of the fecal retention. 

Treatment

Usually, a medical approach is tried first, with surgery reserved for unresponsive cases.  A medical approach involves the use of supplemental fluids, laxatives, stool softeners, colon wall stimulants, and high fiber diets.  These do not correct the underlying cause, but they will help fecal material to pass so the cat does not become constipated and ill. 

The medical approach may be successful for several months or years, but will generally fail at some time.  When this happens, surgery must be considered.  A procedure called subtotal colectomy removes most of the non-functioning part of the colon.  Although this procedure involves removal of most of the colon, the anal sphincter (valve) is left intact so the cat should not lose bowel control.

Since one of the colon's primary responsibilities is to remove excess fluid from the fecal material, the cat that has had a subtotal colectomy will have rather soft stools immediately after surgery.  In addition, there may be several bowel movements each day.  However, after 1-2 months, most cats have soft, but formed, stool and average 3 bowel movements every 2 days.  There should be no loss of fecal control.