Megacolon the scientific term describing a diluted, flaccid and incompetent colon. Megacolon results after chronic constipation or retention of faeces but could also be a congenital dysfunction. The cause of Megacolon results in obstipation (the inability for cats to defecate), due to the fact that faeces are kept inside the colon in a larger diameter. This makes it more difficult for the faeces to exit out of the pelvic area. Faeces will become very hard and dry once water is absorbed by the colon. Should medical treatment no longer be sufficient, then the next viable option in order to treat the condition will be surgery.

Megacolon often falls into two categories: colonic inertia also referred to as functional obstruction, and outlet obstruction which is referred to as mechanical obstruction. Idiopathic (something of unknown cause) megacolon is the most common reason for colonic inertia. A disease of idiopathic origin may cause the colon to lose its normal functionality making it progressively larger as motility decreases. Once the disease advances further, cats then lose the capability defecating.

Outlet obstruction results from a badly healed pelvic fracture, this will affect the normal outflow tract in the pelvis region which will in turn affect the normal discharge of faeces. Other factors such as tumours, hernias and strictures of the anus or rectum will also aid in developing constipation and megacolon

Signs and Symptoms:

Cats that develop idiopathic megacolon are normally between the ages of five to nine years.

Megacolon signs in cats include:

  1. Abdominal discomfort
  2. Decreased appetite
  3. Lethargy
  4. Tenesmus (difficulty in defecation)

Stool present in the cat’s colon if they have megacolon issues is hard and large and can be easily felt by a veterinarian. Your veterinarian will perform a rectal examination to check for old injuries such as a collapsed pelvic fracture, hernias in the interior or exterior of the rectum or colon and any obstructive masses.


Megacolon is diagnosed based upon physical and history examination this is verified by the use of x-rays scanned to the abdomen of the cat’s body. However, when the diagnostic scan is done this must also include a blood examination. This is done to check for metabolic abnormalities. X-rays as in are used to validate the presence of a larger than normal colon and can also be used check for old pelvic fractures, spinal deformities or masses. Abdominal ultrasound, colonoscopy and contrasts of the lower gastrointestinal tract may need to be done to determine the full reason for the megacolon.


The treatment of idiopathic megacolon initially is medical. Cats having this disease must be hydrated (via IV fluids if needed), then an enema will be performed. This is followed by the removal of faeces manually ( deobstipation). This will require a general anaesthesia, as this operation is very painful for the cat. Under no circumstance should you attempt to give your cat an enema yourself unless specifically instructed by your veterinarian. Do not use over-the-counter fleet phosphate as is used for children as this is toxic to cats.

Once the stool is removed, the medical management of the condition begins. Previous treatments that were recommended in the past, included a high fibre diet as well as bulking agents to try make the cat become more “regular”. However, this was proven to be contradictory to a cure and can actually worsen the condition. Low-residue diet has proven to be far more helpful along with prescription medications such as Cisapride and Lactulose. Most cats will respond to this form of therapy at the start. Unfortunately, some cats become resistant to this form of treatment. If medical therapy stops being effective surgery may be required to remove the abnormally enlarged colon.


This surgery is known as a “subtotal colectomy”. This is the removal of a large part of the colon. On occasion a total colectomy is required. This is the removal of the entire colon. A pet may need to be on antibiotics before the surgery as the colon is the part of the intestinal tract which contains the highest concentration of bacteria due to the presence of faeces. Antibiotics help in the prevention of bacterial infections during the surgery.
In a subtotal colectomy, the area of the colon that is affected is cut out (resected). The two ends remaining are stitched back together. Should the affected portion of the bowel not be removed completely, this can result in the a new area of the bowel become dilated, leading obstipation and constipation and starting up the cycle again.

Cats that have pelvic obstruction due to pelvic trauma can be surgically treated by removal of the abnormal pelvic bone (pelvic ostectomy). This will allow the faeces to pass normally. In the unfortunate event, should the megacolon be untreated for more than four to six months in cats with previous pelvic trauma the condition may be irreversible. After this prolonged time the colon might not return to its usual functionality. Cats having untreated pelvic fracture for more than four months may require a subtotal colectomy as well.

Aftercare and Outcome:

During the period of time following a surgical operation, the use of antibiotics will still be used and the cat will be monitored for potential infection. After surgery soft stools and diarrhoea might occur for a few months. Cats will not lose control over defecating after subtotal colectomy, but regular droppings of small pieces of soft stool in and around the litter box as the cat adjusts to life after constipation is common. In some cases, postoperative constipation has been reported. This is rare and is generally treated medically. The need for a second surgery is not often required unless the full affected area of colon was not removed in the first operation. Almost all cats will continue on to a normal life after this surgery and will not require any special diets or medical treatment for this condition thereafter.

Subtotal colectomy in a cat: