Megacolon

What is megacolon? 

The gastrointestinal tract terminates in a tubular organ called the colon. The colon serves as a site for absorption of water and storage of fecal material. It is continuous with the rectum. The walls of the colon contain muscles which are stimulated to contract by nerves from the spinal cord. When the colon contracts, fecal material is pushed out of the body. 

If the nerves to the colon do not function properly, the muscles of the colonic wall will not contract properly. If this happens, the muscles stretch and the colon enlarges in diameter. In addition, the fecal material is not moved out of the body and severe constipation may result. This massive enlargement of the colon and the resulting constipation is called megacolon. The colon may have a diameter 3-4 times that of a normal cat. 

How does megacolon occur? 

An injury to the spinal cord can result in formation of megacolon. Also, mechanical obstruction caused by tumor, foreign bodies, hairballs, and strictures can lead to megacolon. However, in most cases, we cannot determine the reason that the nerves to the colon quit functioning. This disease generally occurs in middle-aged to older cats, but has also been seen in cats only 3-4 years old. 

How is megacolon treated? 

Usually, a medical approach is tried first, with surgery reserved for unresponsive cases. A medical approach involves the use of laxatives, stool softeners, colon wall stimulants, and high fiber diets. These do not correct the underlying cause, but they do allow 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 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. 

Can the cat function without its colon? 

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 two days. There should be no loss of fecal control.

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