What Are Colorectal Polyps?

The colon and rectum are both part of the digestive system, and together with the anus are known as the large intestine. Once food enters the body it is broken down in the stomach before being passed on to the small intestine. The breakdown of food continues in the small intestine, and it is here that most of the nutrients in our food are absorbed into the body. The leftover material, which is mostly liquid, then moves into the colon where water and some further nutrients are absorbed.

The remaining waste (known as “stool”, “feces”, or “poo”) is stored in the rectum before it is passed out of the body via the anus. Colorectal polyps are small clumps of cells that form on the lining of the colon and/or rectum. Most colorectal polyps are harmless (benign) and do not cause any symptoms, but over time some polyps can begin to grow out of control leading to colorectal cancer.

What Is Colorectal Cancer?

Colorectal cancer is one of the most common types of cancer worldwide, with incidence varying widely between different regions and countries. Although colorectal cancer is usually diagnosed in people older than 50 years of age, it can occur in people who are younger than 50 years, particularly if they have a family history of colorectal cancer or have certain conditions that can be inherited. As well as genetic conditions, it is known that lifestyle choices such as eating a diet that is high in processed and red meat are linked to increased risk of developing it.

Common signs and symptoms of colorectal cancer include a persistent change in bowel habits (such as diarrhea, constipation, and/or a change in stool consistency that does not clear up after a short period of time), rectal bleeding or blood in the stool, a feeling that the bowel has not been completely emptied of stool when going to the toilet, losing weight without trying, a persistent feeling of weakness or tiredness, and discomfort in the abdomen area (the area between the chest and the pelvis) that does not go away.

Why Is Colorectal Polyp Size Important?

Research has shown that the larger the size of a colorectal polyp, the greater the chance that it will become cancerous. Changes in genes (mutations) that take place in the cells of a colorectal polyp over time can mean that they become able to grow more quickly and live longer, resulting in the polyp growing larger. If a polyp that is beginning to grow too large and too quickly is identified, and removed from the colon or rectum before it becomes cancerous and begins to spread, the development of colorectal cancer is prevented. As a result, the sizes of polyps influence how often follow-up screening will be conducted and whether or not they will need to be removed.

What Did This Study Investigate?

Because the size of a colorectal polyp can indicate whether or not it is likely to become cancerous, it is important that polyp size is estimated correctly. Polyp size can be assessed by endoscopy, a medical procedure that uses a long, thin, flexible tube with a small camera inside (called an endoscope) to look inside the body. The two types of endoscopy that are most commonly used to assess colorectal polyps are colonoscopy and flexible sigmoidoscopy.

Colonoscopy involves using an endoscope to assess the entire length of the colon, while flexible sigmoidoscopy only looks at the lower third. Most judgments about the sizes of colorectal polyps are made by endoscopists estimating polyp sizes by sight, but this means that there is a risk that their estimates may be wrong. Correctly estimating the sizes of polyps is difficult because endoscopes have “fisheye lenses” (also called an ultra-wide lens), which tend to curve straight lines and distort the images that endoscopists see. This means that objects such as polyps at the center of the display can appear larger than they really are, while things at the outer edge of the display can appear smaller. Although is has been suggested that forceps be used to measure polyps during endoscopy procedures, their use can make them more complicated and time-consuming.

To get around these problems, a new type of endoscope called a virtual scale endoscope (VSE) has been developed. A VSE is able to project a red laser dot onto the surface of the colon or rectum that changes positing according to the distance between the polyp and the end of the endoscope. The software that processes the VSE’s images then detects the position of the red laser dot and uses it to display a virtual scale (this can be linear, a bit like a ruler, or circular) on the image that is produced to help the endoscopist estimate polyp size in real time during the procedure. The authors of this study looked at whether polyp measurements made using a VSE were accurate, and also investigated whether using the images produced could be used as a teaching aid to help endoscopists better estimate polyp sizes.

How Was The Study Conducted?

The authors carried out two studies. The first study compared the sizes of polyps as measured using a VSE before they were removed from the colon with their actual size as measured with a ruler after they were removed. The second study involved 14 endoscopists with differing levels of experience estimating the sizes of 42 polyps in a pre-test before receiving a lecture about how to measure colorectal polyps using VSE images.

The endoscopists were categorized as beginners, intermediates, or experienced based on the number of years of experience that they had. The lecture that they received included the endoscopists being shown the correct sizes of the polyps that they had been asked to estimate in the pre-test, together with VSE images with a virtual scale, and each endoscopist received an explanation of how sizing errors were being introduced. The endoscopists then had a 1-month training period where they could practice what they had learned before doing a post-test using the original images (which were shown to them in an order that differed from the order shown in the pre-test to try to reduce bias).

What Did The Study Show?

The results of the first study indicated that there was agreement between the polyp size estimates produced using a VSE and the actual sizes of the polyps. In the second study, the accuracy of the beginner and intermediate endoscopists in measuring polyp sizes was significantly better in the test conducted after the training period than in the pre-test, with accuracy improving by approximately 50% in some cases.

These results indicate that VSEs can accurately measure colorectal polyp sizes before they are removed from the colon and that the images that they produce are useful tools with which to train endoscopists in the first few years of their careers, suggesting that VSE use has the potential to increase the accuracy of polyp measurement during endoscopy and, as a consequence, improve the detection of polyps that are beginning to grow out of control.

Note: This post is based on an article that is not open-access; i.e., only the abstract is freely available.