Changes

Megacolon is a state of permanently increased diameter of the large bowel. This change in intestinal structure leads to abnormal function, including reduced colonic motility and chronic constipation. The condition most commonly occurs in cats and dogs, but pigs can also be afffected. White foals suffering congenital colonic agangliosis, an autosomal recessive trait, may develop secondary megacolon.

Megacolon is a state of permanently increased diameter of the large bowel. This change in intestinal structure leads to abnormal function, including reduced colonic motility and chronic constipation. The condition most commonly occurs in cats and dogs, but pigs can also be afffected. White foals suffering congenital colonic agangliosis, an autosomal recessive trait, may develop secondary megacolon.

In small animals, megacolon may be congenital or acquired, which may be idiopathic. Although well described as Hirschsprung's disease in human medicine, congenital megacolon is less understood in cats. It was first recognised in 1998¹, and is thought to be caused by aganglionosis of a colonic segment, leading to persistent smooth muscle contraction the affected region and dilation of the colon proximal to this. Acquired megacolon is more common than the congenital form, and in cats this is most often idiopathic. The true cause of "idiopathic" megacolon is thought to be an intrinsic defect in colonic smooth muscle function².

In small animals, megacolon may be congenital or acquired, which may be idiopathic. Although well described as Hirschsprung's disease in human medicine, congenital megacolon is less understood in cats. It was first recognised in 1998¹, and is thought to be caused by aganglionosis of a colonic segment, leading to persistent smooth muscle contraction the affected region and dilation of the colon proximal to this. Acquired megacolon is more common than the congenital form, and in cats this is most often idiopathic. The true cause of "idiopathic" megacolon is thought to be an intrinsic defect in colonic smooth muscle function². Aquired megacolon can occur in both cats and dogs as a sequel to any disease or lesion that interferes with normal defecation: faecal retention caused dilatation of the colon and impairs colonic motility. Causes could include neuromuscular abnormalities (spinal cord disease, intervertebral disk disease, dysautonomia, trauma), metabolic disorders (severe dehydration, hypokalaemia), drug therapy (vincristine, anticholinergics, barium), mechanical obstruction (pelvic fracture malunion, foreign bodies, stricture, anal/rectal atresia) and conditions causeing dyschezia (anal sacculitus, perianal fistula, trauma preventing posturing, procititis). After megacolon has persisted for several months, it is unlikely that normal colonic motility will be restored after resolution of the underlying cause. In many cases, the aetiology of megacolon is not determined.

 

 

Acquired megacolon also occurs

as a sequel to any lesion or disease

that prevents normal defecation for

a prolonged period of time. If

megacolon has persisted chronically

for several months or longer, the

an underlying cause is unlikely.Chronic retention of faeces and distension of the colon irreversibly damages colonic motility to cause acquired megacolon. Idiopathic megacolon is seen primarily in cats, and it has recently been suggested this condition may involve changes to normal colonic smooth muscle function. In many cases, the aetiology of megacolon is not determined.

 

==Signalment==

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