Colon, rectal polyps

A polyp is a lump projecting above the surface of the intestinal lining.  The term is no more specific than that and therefore must be preceded by another term identifying the type of polyp, such as adenomatous polyp or hyperplastic polyp.  Polyps may occur in a variety of shapes and sizes.

It is believed that most cancers of the colon and rectum develop from polyps.  This does not mean, however, that most polyps turn into cancer.  Some types of polyps have no potential to transform into cancers.  Others, called adenomatous polyps, may undergo a malignant transformation in time.  When a polyp is found, it is essential that it be removed and submitted for microscopic assessment and classification so that appropriate treatment and follow-up can be planned.

Types of Polyps

Hyperplastic polyps
Hyperplastic polyps are the most common form of colorectal polyp.  They are usually small (less than 10 mm in diameter), pale gray, flat bumps found on the surface of the large bowel and particularly in the rectum.  Hyperplastic polyps are caused by a localized delay of sloughing of the intestinal lining cells so that a pile of cells builds up.  Hyperplastic polyps tend to come and go as the clump of cells eventually sloughs off.  Reliable naked eye distinction of hyperplastic polyps from the more important adenomatous polyps is not always possible, so they should be removed or at least biopsied for an accurate diagnosis.  It is currently believed that hyperplastic polyps have no potential to become cancers and hence require no treatment nor follow-up.

Inflammatory polyps
Inflammatory polyps are the result of inflammation in the colon or rectum from infection or from inflammatory diseases of the bowel (ulcerative colitis and Crohn’s disease).  These polyps have no potential to become malignant (although there is an increased risk of colon cancer among patients with longstanding ulcerative colitis). Inflammatory polyps resolve when the disease is treated and the inflammation and swelling subside.

Hamartomatous polyps
Hamartomatous polyps arise from an error in the architecture of cells, normal cells arranged in an abnormal, disorganized fashion.  The abnormality is present at birth, but the polyps themselves may not become apparent until the tissues undergo enough growth for a lump to form.  Hamartomatous polyps have little, if any, malignant potential.

Adenomatous polyps (adenomas)
Adenomas are the polyps that have potential to become cancers.  The World Health Organization has divided adenomas into three types: tubular adenomas, tubulovillous adenomas and villous adenomas.

  • A tubular adenoma is so named because its surface looks like branching tubes when viewed under a microscope.  When viewed by the naked eye, the head is bright red and smooth.  Frequently, tubular adenomas are a lollipop shape (hang from the bowel lining on a stalk) and can usually be removed easily with a colonoscope. They are the least likely of the adenomas to contain or develop cancer.
  • A villous adenoma is a polyp whose surface displays long, finger-like projections when viewed under the microscope.  To the naked eye, it has a carpet-like surface. Villous adenomas tend to be flat, wide and broad-based.  They can be very large and in some cases can completely carpet a portion of the bowel surface.  They are most commonly found in the rectum.  They often produce mucus that is noted in bowel movements.  Villous adenomas have the most malignant potential of the adenoma group.
  • A tubulovillous adenoma is an adenoma which has a mixture of tubular and villous surface characteristics and has shape and malignancy characteristics that lie between the tubular and villous adenomas.

© Pezim Clinic, Vancouver, British Columbia, Canada