Constipation is not a disease, rather a sign of many diseases. It is defined as infrequent and difficult passage of feces with the retention of hard feces in the colon and rectum. Prolonged retention of feces in the colon leads to increased absorption of water. Two distinct groups of feline patients have been recognized--those with colonic inertia (idiopathic megacolon) and those with outlet obstruction.

Obstipation is an intractable form of constipation, where fecal impaction is severe and defecation is impossible.

Megacolon is defined as distension of the large intestine. In the cat and dog this condition is primarily an acquired disorder affecting adults. Mechanical obstruction from foreign bodies, intramural or extramural masses, pelvic fracture malunion, or neurological deficits can result in secondary megacolon.

Normally, cats can retain feces in the colon for several days without harm. Mechanical obstruction to the passage of feces can lead to prolonged retention of feces and possible formation of concretions. These hard and impacted feces are difficult to pass and, if not removed, may cause the colon to become distended.

If the distension is chronic, irreversible colonic hypomotility can result. The duration and degree of colonic distension needed to produce this change is unknown. Results of one limited study suggest that sufficient motility may return if mechanical obstruction caused by a pelvic malunion is corrected within 6 months.

Beyond 6 months, intramural myoneural changes secondary to chronic distension prevent return to normal function even after the obstruction is relieved.

Lumbosacral spinal cord disease can result in a chronically constipated cat by causing disruption of the innervation of the colon. The hypomotility that results can lead to retention of feces with severe impaction and megacolon. Manx cats with partial or complete absence of the sacral and caudal spinal cord may have megacolon with concurrent urinary or fecal incontinence.

Another neurological condition associated with constipation in cats is dysautonomia (Key-Gaskell syndrome). This progressive polyneuropathy of the autonomic nervous system is seen in the older cat.

Megacolon resulting from unknown causes (idiopathic megacolon) is probably the most common form of acquired megacolon in cats leading to intractable constipation. The cause is unknown.

HISTORY AND CLINICAL SIGNS

Cats with a history of trauma may have a constipation disorder related to either a pelvic fracture or lumbosacral disease. Cats without any known form of trauma probably suffer from the idiopathic form of megacolon. These cats have recurring signs of constipation. Which progresses to obstipation over time. Most of the cats are adults. Many have had nonspecific and subtle signs related to fecal impaction. They may go several days without defecating but not have constipation severe enough to warrant veterinary attention. Historically, most owners complain about their cat's tenesmus and failure to defecate in spite of frequent attempts.

Systemic signs may be present depending on the duration of the constipation. Physical examination findings in the mildly affected cat with constipation may be unremarkable. However, in cases of long standing constipation, the cat can become anorectic, depressed, emaciated, dehydrated and anemic.

Some cats will appear to unthrifty and have perineal soiling. Abdominal palpation will sometimes elicit discomfort and will reveal a distended colon filled with hard fecal material. Rectal palpation should be done to evaluate for a narrowed pelvic canal due to previous trauma or a stricture of the rectum or anus. A rectal examination will also help in defining the presence of a perineal hernia which in cats may be the underlying cause of the cat's constipation.

DIAGNOSIS

The diagnosis of megacolon is based on the history of tenesmus, palpation of a large feces-filled colon, and abdominal and pelvic radiographs. Radiography may uncover any predisposing causes such as pelvic canal stenosis secondary to pelvic trauma, soft tissue masses, foreign material or lumbosacral lesions. Absence of any obvious predisposing primary disorder allows us to label the condition "idiopathic megacolon".

Upper GI barium studies or barium enemas can be done but should follow the digital removal of the impaction and multiple enemas. This will either confirm megacolon or define any strictures or suspected neoplasia. Endoscopy of ht colon may be indicated if inflammatory or neoplastic diseases are suspected.

TREATMENT AND A SUMMARY OF THINGS WE HAVE LEARNED

Cats with chronic constipation are treated symptomatically. We have had good success with the use of a laxative (lactulose) and cisapride (prokinetic agent for the colon). However, some cats eventually become refractory to these drugs and surgery may be necessary. When an underlying disorder can be identified, (e.g., pelvic fracture malunion), correction of the primary problem may alleviate the problem. However, we believe it is better in these cases to perform a less invasive subtotal colectomy.

When we first started performing subtotal colectomies approximately 20 years ago, we present this procedure to owners as a "salvage" procedure. However, our great success over the past 2 decades now allows us to encourage owners to consider this procedure as an excellent alternative assuming aggressive medical therapy has been attempted.

Although aggressive medical therapy is often successful, some owners will choose to have their cat undergo surgery. For these owners, the medical treatment either becomes too cumbersome or the cat begins to hide whenever the owners approach them with their medication. Some owners complain that the cat eventually remains hidden and no longer wishes to socialize with them.

We still believe it is necessary to preserve the ileocolic valve (ICV) when possible. Our experience clearly shows that cats with ICV removal take longer to recovery from the surgery. Approximately 5-10 % of the cats I have done cannot have their ICV preserved usually due to a large amount of fat within the abdomen.

Many years ago, I thought it important to fast these cats 2-3 days after surgery and, when feeding was restored, I recommended a special low-residue food diets. I now feed them the day after surgery and will try any diet to encourage early return to eating. This early return to feeding optimizes wound healing and good intestinal function. I also recommend the owner encourage their cat to eat anything it desires after returning to their home environment.

This is considered a "clean-contaminated" surgery and therefore antimicrobial prophylaxis is indicated. I prefer a second generation injectable cephalosporin (cefoxitin) given intravenously. I start 20-30 minutes preoperatively and repeat it once 3 hours later. This is done in concert with good surgical technique that minimizes intraoperative contamination.

After performing over approximately 150 cases, I have had 2 animals form a postoperative stricture. The cats usually had severe tenesmus and discomfort within 2 weeks of surgery. Although a barium enema will help define the lesion, a rectal examination has been adequate to diagnose this condition. To treat this condition, we used balloon dilation. Both cats required 3 dilation procedures at 2-3 day intervals. Any remaining small amount of stricture can usually be corrected digitally while doing a rectal examination.

In my experience, a significant number of these animals have a concurrent perineal hernia, either unilaterally or bilaterally. This does not appear to be a clinically significant problem after the cat undergoes a subtotal colectomy. This is likely due to the soft consistency of the stool that remains after the surgery.

Overall, the prognosis following a subtotal colectomy remains excellent, although we still encourage appropriate medical therapy be attempted first.

References

1.  Bright RM, Burrows CE: Subtotal colectomy for treatment of acquired megacolon in the dog and cat Jour of the Amer Vet Med Assoc 188: 1412-1416, 1986

2.  Matthiesen DT, Scavelli TD, Whitney, WO: Subtotal colectomy for the treatment of obstipation secondary to pelvic fracture malunion in cats Vet Surgery 20: 113-116, 1991

3.  Rosen E et al: Subtotal colectomy for treatment of chronic constipation associated with idiopathic megacolon in cats: 38 cases (1979-1985) Jour of the Amer Vet Med Assoc 193: 850-855, 1988

4.  De Haan JJ, Ellison GW, Bellah, JR: Surgical correction of idiopathic megacolon in cats Feline Pract 20: 6-11, 1992