Megacolon in Cats

Yes, you read that title correctly. Megacolon is a condition that occurs most often in cats and is basically an extra mega-sized colon. More specifically, a chronically enlarged colon that is often filled with dried feces is called a megacolon.

Under normal circumstances, the colon, or large intestines, serves as a site for absorption of water and storage of feces. When the movement of feces is delayed and feces remain in the colon for prolonged periods, the colon continues to extract water from the feces resulting in dry and hard stool that are difficult to pass. Subsequently, more and more feces accumulate, which stretches the colon and greatly increases its size.

Causes

The most common cause is unrelieved or recurrent constipation. When this is the case, constipation itself is the cause of the megacolon. Constipation can be caused by a number of things—an abnormal narrowing of the pelvis (either congenital or resulting from injury), paralysis of the anal region, chronic GI diseases, and a number of diseases that cause recurrent dehydration. Physical obstruction caused by tumors, foreign bodies, hairballs, and strictures may be involved. With all of these causes, if constipation is not relieved, the distended colon loses normal muscle strength, which exacerbates the constipation.

A second form is one in which constipation is an effect, not the cause of megacolon. This happens when a patient loses proper nerve function within the colon which means the muscles of the colon wall will not function properly to pass along stool. The muscles become stretched and the colon enlarges in diameter, often significantly. Fecal material accumulates and does not get pushed out, resulting in severe constipation or worse, obstipation, where the patient stops defecating all together.

Clinical Signs

The most common sign is the obvious one -- severe constipation. Some cats vomit and lose their appetite. The patient may become dehydrated and lethargic.

Diagnosis

On physical examination, your vet may be able to palpate an enlarged colon unless your cat is overweight. X-rays of the abdomen and spine are often recommended to look for underlying problems and to assess the degree of constipation. Routine laboratory tests and an abdominal ultrasound are often recommended as well.

Treatment

Treatment of the constipation and megacolon involves several options depending upon the cause and severity. A medical approach is usually tried first but surgery may be necessary for severe or chronic cases.

A medical approach involves the use of laxatives, colon wall stimulants, enemas, and high fiber diets. While these don’t correct the underlying cause, they will hopefully allow fecal material to pass so the cat does not become further constipated. If megacolon is caught early, this may be enough to return the cat to normalcy but recurrence occurs frequently.

More severe constipation often requires anesthesia and administration of enemas combined with manual extraction (the veterinarian using their fingers). This may take several attempts to relieve the constipation.

If the problem continues for months or years, the colon may eventually stop functioning. Partial removal of the colon may be beneficial when the colon ceases to function.

Prognosis

The outlook for cats with megacolon that are treated medically is uncertain and really is best when evaluated case-by-case. If muscle function returns and constipation resolves with therapy, the prognosis is reasonable; however, recurrence is common in many cats. The prognosis for recovery from surgery is good if no complications occur. The prognosis is worse when megacolon occurs in very young kittens.

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