Feline megacolon and colonic neoplasia (Proceedings)
Megacolon occurs more frequently in cats than dogs and is usually seen in middle-aged to geriatric cats. The ascending, transverse, and descending colon are chronically large in diameter and filled with dry stool. A congenital form of the disease has been seen especially in Manx cats with rectal/anal atresia and a sacral spinal deformity. An acquired form of the disease has been seen secondary to mechanical obstruction caused by malunion of pelvic fractures that have not had surgical treatment. Mechanical obstructions such as those caused by pelvic fractures may be relieved by removal of the cause of the obstruction if the abnormality is corrected within approximately 6 months; beyond that time frame irreversible changes apparently occur within the myoneural structure of the colon and obstruction persists even if the cause is treated effectively. Another unusual cause of acquired megacolon reported on several occasions is obstruction caused by uterine horn remnants following ovariohysterectomy in the female. Constipation has also been reported as a presenting sign in animals that are hypercalcemic with primary hyperparathyroidism.
Idiopathic megacolon is the most common form of the disease seen in cats. This disease is thought to be caused by an abnormality in the smooth muscle of the colon. Investigators at the University of Pennsylvania have shown that the colon of affected cats does NOT have normal motility as a result of a muscular rather than nervous abnormality. Some have suggested that anything causing pain or discomfort that may inhibit the animal from defecating may be a predisposing cause. Such causes could be spinal, pelvic, or rear limb related. Whatever the cause, as the dry stool continues to accumulate, colonic distension causes irreversible change in colonic smooth muscle and nerves and colonic inertia results. Medical management is variably (charitable word) effective in my experience. Surgical treatment with subtotal colectomy has been a very rewarding procedure for owners AND their cats for this disease over the past 15 years.
A. Clinical Signs
Interestingly, several female cats have been reported with megacolon caused by extramural obstruction as a result of stricture formation following ovariohysterectomy 4-6 weeks previously. The stricture in all cases has been reported to be caused by uterine horns remaining after incomplete ovariohysterectomy.
B. Conservative/Medical Management
Inevitably, many animals with megacolon begin to have episodes of obstipation closer and closer togeher and the owner, cat, and veterinarian tire of anesthetic episodes etc. If you sense the case headed this way and MOST do, consider saving the owner, cat, and you from further episodes and recommend surgery.