What is megacolon?
Megacolon is a term used to described a very dilated,flaccid,incompetent colon.
This usually occurs secondary to chronic constipation & retention of feces, but may be congenial dysfunction.This feces also become very dry and hard,as colon absorbs water.
Etiology
The most common cause for outlet obstruction is obstruction due to poorly healed pelvic fractures, which impinge on the outflow tract of the pelvis and prevent the normal passage of feces. Tumors, strictures, and hernias of the rectum/anus can also contribute to the development of megacolon or constipation.Megacolon is secondary to chronic inertia (functional obstruction) or outlet obstruction.
Signs and symptoms
Cats affected with idiopathic megacolon are usually between 5–9 years old. Diagnosing the condition usually happens long after constipation has been present, especially in a multiple cat household, or when cats are indoor/outdoor. In these cases, owners may not be aware of their cat’s normal bowel habits.
Cats affected by megacolon may show the following signs:
-abdominal discomfort
-decreased appetite
-lethargy
-tenesmus (straining to defecate)
The stool present in the colon is large and firm, and is easily palpable (a veterinarian can feel it easily). It is important that your veterinarian perform a rectal exam to check for old collapsed pelvic fractures, obstructive masses, or hernias located either inside or outside of the colon or rectum.
Diagnosis
Megacolon most commonly occurs in middle-aged, male, domestic shorthair cats. Stools may appear smaller than normal or be absent during episodes of constipation. Usually, affected cats pass a large amount of dry and hard stool one to three times per week. Other symptoms include decreased appetite, lethargy, weight loss, dehydration, abdominal pain, straining to defecate, vomiting and anemia.
Photo courtesy of Hill’s Pet Nutrition
The diagnosis of megacolon is based on clinical history and physical examination findings of a very distended colon with feces. A simple digital rectal examination will rule out masses or an obstruction within the pelvic canal that may be causing the megacolon.
Abdominal X-rays are used to confirm the presence of a colon distended with feces and to rule out other diseases, such as a malformed pelvis or a tumor within the abdomen or colon.
Abdominal ultrasound and colonoscopy are other diagnostics that are less frequently performed but may provide necessary information to diagnose an underlying cause of megacolon.
Because megacolon in kittens may be caused by a malfunctioning thyroid gland, a blood test may be recommended in these patients. Blood testing such as a complete blood count, chemistry profile and urinalysis are done prior to surgery to ensure that your companion can be safely anesthetized.
Treatment
Medical treatment
-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 anesthesia, as it is extremely painful for an awake cat.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.
-Best medical management includes a low-residue diet and prescription medications such as lactulose and cisapride.Lactulose is a mild cathartic (helps speed dedication) and is a stool softner.Cisapride stimulates colonic motility.
-When medical therapy is no longer effective,surgery to remove the enlarged colon is recommended.
Surgical treatment
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 surgery.
In subtotal colectomy, the entire affected colon is resected (cut out) and the two remaining ends are sutured back together. Failure to remove an affected portion of bowel can cause formation of a new dilated area of 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
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