Megacolon

Description

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, acquired or 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.

Congenital megacolon in small animals has not been well studied, but is thought to be due to an absence of colonic ganglionic cells. 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.

There are many potential underlying caused for chronic faecal retention and thus acquired megacolon. In addition to the abnormalities of the caudal spinal cord responsible for congenital megacolon,

Signalment

Cats may suffer idiopathic megacolon, and both cats and dogs may develop the acquired form. Congenital megacolon is not well studied in cats and dogs. Any age or sex of animal may aquired megacolon, but idiopathic megacolon is more common in middle-aged to older cats. There is also some evidence for an increased risk of megacolon in Manx cats.

References

1. Rosin, E et al, (1988) Subtotal colectomy for treatment of chronic constipation associated with idiopathic megacolon in cats: 38 cases (1979-1895). Journal of the American Veterinary Medical Association 193, 850-853.