For idiopathic megacolon, initial management is medical. These cats should be appropriately hydrated (IV fluids if dehydrated), then an enema and deobstipation (manual removal of feces) should be performed. This almost always requires general anaesthesia, as it is extremely painful for an awake cat. NEVER attempt to give a cat an enema at home unless instructed by your veterinarian, and NEVER use an over-the-counter Fleet phosphate enema (infant enema), which is toxic to cats.
After the stool has been removed, medical management begins. In the past, a high fibre diet and bulking agents such as Metamucil and fibre pills were recommended in an effort to make the cat more “regular.” These are actually contraindicated and can worsen the signs. Best medical management includes a low-residue diet (your veterinarian can suggest low-residue prescription diets) and prescription medications such as lactulose and cisapride. Lactulose is a mild cathartic (helps speed defecation) and is a stool softener. Cisapride stimulates colonic motility (propulsion). The low residue diet helps to stimulate the colonic cells without an increase in bulk. Most cats will initially respond to this therapy, but some will eventually become resistant to treatment. When medical therapy is no longer effective, surgery to remove the enlarged colon is recommended.
The surgery is referred to as a “subtotal colectomy” (removal of most, but not all, of the colon), although occasionally a total colectomy (removal of the entire colon) is required. Before surgery, your pet may be started on antibiotics, because the colon, containing feces, is the most bacteria-laden part of the intestinal tract. Antibiotics help to prevent bacterial infection at the surgery.
In subtotal colectomy, the entire affected colon is resected (cut out) and the two remaining ends are stitched back together. Failure to remove an affected portion of the bowel can cause the formation of a new dilated area of the bowel, leading to recurrence of clinical signs of constipation and obstipation. Sub-total colectomy is a challenging surgical procedure.
Cats with pelvic obstruction secondary to pelvic trauma can be treated by removal of the abnormal pelvic bones (pelvic ostectomy) to allow normal passage of feces again. Unfortunately, if the megacolon has been present for greater than four to six months, dilation and loss of function may be irreversible. The colon is not able to return to normal function after this extended period of time. Therefore, most cats with impacting pelvic fractures are also treated with the same surgery (subtotal colectomy).