What are Colorectal Polyps?

By BSc (Hons)

A colorectal polyp is a growth that may present on the lining of the colon or rectum. While these are fairly common and affect 15-20% of the UK population, they are not usually associated with symptoms. Only when a polyp is big enough to cause a bowel obstruction can it result in nausea, vomiting and severe constipation.

Importantly, the best course of action when a polyp is found is dependent upon the number, type, size, and location of the polyp. While bowel polyps are not usually cancerous, if they're discovered they'll need to be removed and can be done completely and safely, as some will eventually progress to cancer if left untreated.

Polyps are either pedunculated (attached to the intestinal wall by a stalk) or sessile (growing directly from the wall). On the whole, there are typically three types of polyps:

  • Adenomatous (and malignant),
  • Hamartomatous and,
  • Inflammatory.

Adenomatous (Neoplastic) polyp

These are of greatest concern as they have the potential to become cancerous after many years. Such adenomas are histologically classified as tubular, tubulovillous, or villous. These adenomas show different growth patterns of which the two major ones are tubular and villous with a mixture of these growth patterns giving a tubulovillous adenoma.

Generally, most small adenomas (<1/2 inch) have a tubular growth pattern whilst the larger ones may have a villous growth pattern and increased likelihood of becoming cancerous.

The likelihood of cancer in an adenomatous polyp at the time of discovery is related to histologic type, size, and degree of dysplasia; a 1.5-cm tubular adenoma has a 2% risk of containing a cancer compared to a 35% risk in 3-cm villous adenomas. A somewhat more aggressive type of adenoma called a serrated adenoma may develop from hyperplastic polyps.

Following the removal of an adenoma people will need a follow-up examination; new polyps may develop over time which will also need to be removed.

Hamartomatous polyp

A hamartoma is defined as a tumor-like malformation that presents due to an error in the development at numerous sites where growth occurs. They are benign and may not cause any problems, usually identified incidentally as they tend to grow at the normal and non-pathological rate of the host tissue, rarely causing problems such as compression.

This does not mean that hamartomas are harmless. Morbidity can arise by means of a variety of mechanisms such as obstruction, infection, infarction, hemorrhage and iron deficiency anemia amongst others.

While it may resemble a neoplasm, a hamartoma does not usually show a tendency to evolve into one. With this said, occurrences of neoplastic evolution have been reported in patients suffering from von Recklinghausen disease. Interestingly, an association has also been established between neoplasms and hamartomas which can be seen in some patients with Peutz-Jeghers syndrome. While the polyps themselves carry little potential for malignancy, there is still a 15% chance of colonic malignancy because of potential coexisting adenomas.

Inflammatory polyp

These are polyps which show an association with inflammatory conditions such as Crohn’s disease and Ulcerative Colitis. Although the polyps themselves are not a particularly significant threat, suffering from these two colon disorders increases the overall risk of colon cancer.

Risk Factors for Colorectal Cancer

It is possible for anyone to get colorectal cancer however it is most commonly reported in people over age 50. Risk factors for colorectal cancer include:

  • A history (personal or family) of colorectal cancer or polyps
  • Unhealthy diet (abundant in red and processed meats)
  • Inflammatory bowel disease (such as Crohn's disease or ulcerative colitis)
  • Inherited conditions (including hereditary non-polyposis colon cancer and familial adenomatous polyposis)
  • Obesity
  • Smoking
  • A sedentary lifestyle
  • Alcohol abuse
  • Type 2 diabetes


Last Updated: Nov 23, 2015

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