Megacolon is described as a chronic or persistent dilation of the large intestine (particularly the colon) and hypomotility (abnormally slow movement/motion) that is associated with constipation. Megacolon is generally termed idiopathic megacolon due to its unidentifiable cause.


Megacolon is usually diagnosed with an animal (generally a feline) presenting for constipation, and in extreme cases, obstipation. Constipation is a condition in which the animal has difficulty passing a bowel movement and in which the fecal matter may be very hard and dry. Obstipation is an extreme form of constipation where the animal may not be able to pass any fecal matter. These animals may also be depressed, anorexic, experiencing weakness, lethargic, having poor hair coat, vomiting, losing weight and in some cases having occasional bouts of bloody/watery diarrhea.

When fecal matter remains in the colon for a prolonged period of time, it will dehydrate and solidify, making it hardened and difficult/painful to pass. The collected feces then can become so large and hard to pass that the ability to make passage through the pelvic canal is impossible. If left untreated, the prolonged distention of the colon can cause problems that cannot be fixed in the colonic smooth muscle and nerves.

Differential Diagnosis

Other diagnoses than idiopathic megacolon must be reviewed in order to make a proper diagnosis. These other causes of megacolon include: congential, obstructive, neurological, and systemic causes. The above could be caused by drugs, severe dehydration, environmental changes, perianal pain, inappropriate diet, colorectal masses, hypercalcemia (increased calcium level in the blood), hypokalemia (decreased potassium level in the blood), hypothyroidism (decreased thyroid levels), and spinal cord or nerve damage.

Procedures Used For Megacolon Diagnosis

Abdominal palpation will reveal a distended colon as well as rectal examination revealing hard feces. The veterinarian will then take abdominal radiographs to rule out obstructive diseases. Radiographs of the animal suffering from megacolon will reveal the distended colon impacted with fecal material. In some cases, ultrasound will also be used to confirm the diagnosis of megacolon and rule out other causes.

Medical Management

The constipated/obstipated patient should always be treated medically before deciding the need for surgery. Once megacolon has developed, it becomes very difficult to control medically. At presentation, the colon should be evacuated by use of enemas or manual removal. It is then recommended that the patient be placed on a high fiber diet, laxatives, and stool softeners. Surgery is indicated for this condition with recurrent constipation/obstipation.

Surgical Treatment of Megacolon

The surgical procedure of megacolon is a subtotal colectomy where most of the colon is removed. This procedure of taking away the colon and reconnecting the remaining intestine is called resection and anastomosis. The newly formed intestine is carefully sutured together and checked for any place a leak might occur. This now shortens the transit time for stool and lessons the chance for constipation.

Postoperative Care

After surgery the patient is maintained on IV fluids to ensure hydration and given analgesics for any pain/discomfort. To allow the bowel time to heal, food is withheld for about 24 hours. The patient will then be offered food, although it may remain anorexic for a few days postop. Liquid or tar-like feces are to be expected following surgery. The feces should gradually change from diarrhea to soft/formed stools within 6 weeks. Always keep a clean litterbox to encourage defecation.

Long-term results of the subtotal colectomy for idiopathic megacolon range from good to excellent. Without surgery, persistent constipation will necessitate recurrent enemas.