A polyp is a lump projecting above the surface of the intestinal lining.  Polyps are important because we think that the majority of colorectal cancers are due to polyps that have transformed into a cancer.  But only certain types of polyps do this so we need to examine this issue of polyps more fully in order to know which polyps are of concern.  The most important thing to know about a polyp is the type of tissue it is made up of.  The second thing to know about a polyp is its shape, since that can have some impact on how significant it is and how difficult it will be to get rid of.

Classifying polyps by cell type
While there are a variety of different types of polyps based on cell type, there are really only two kinds that most patients need to be aware of, adenomatous polyps (adenomas) and hyperplastic polyps.

Adenomas are the polyps that have the potential to become cancers.  They are true growths of cells.  When we are talking about the ‘polyp – cancer sequence’, we are talking about adenomas.  We used to think that adenomas occurred in about 4% of people.  Now we think they are even more common, incurring in up to 20% in otherwise healthy individuals.

Hyperplastic polyps are the other common type of 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.  As such, they tend to come and go.  They are not true growths of cells and we think the vast majority of hyperplastic polyps do not have the potential to become malignant.  However, in the last decade, a subclassification of hyperplastic polyps have been identified as having malignant potential.  Pathologists are now referring to such polyps as ‘serrated adenomas’.

In general, we can’t really tell what kind of tissue a polyp is made up of until we biopsy it or remove it and have the tissue examined under a microscope by a pathologist.  Because of this, most polyps should be removed or biopsied.

Classifying a polyp by shape
Polyps that stick up from the bowel lining like a lollipop are known as pedunculated polyps.  The head of the polyp sits up on a ‘stalk’.  Polyps that are flatter and have no stalk are called sessile polyps.  The shape is important for a couple of reasons.  Firstly, pedunculated polyps are easier to remove since the colonoscopist can get a wire around the stalk and cut through it.  If the polyp is sessile, the colonoscopist may not be able to get a wire around it so removing such a polyp is harder, and is more likely to be associate with an injury during colonoscopic polypectomy.  The second reason the shape is important is that if the polyp is an adenoma, there is a higher likelihood that there may be malignancy in it if it is sessile than if it is pedunculated.

Hyperplastic polyps are usually smaller than a single centimeter and are almost always sessile since they are just too small to have a stalk.  Adenomas, the more important kind of polyp, can be either pedunculated ore sessile.  So one might hear doctors talking about ‘a sessile adenoma’ or ‘a pedunculated adenoma’.