Villous adenoma of the colon and rectum

by Ipshita Kak MD FRCPC
December 4, 2022

What is a villous adenoma?

A villous adenoma (VA) is a non-cancerous growth in the colon. It develops from the cells that cover the inside surface of the colon. These adenomas can develop anywhere along the length of the colon from the cecum to the rectum. All VAs are associated with an increased risk of developing a type of colon cancer called adenocarcinoma over time.

Does villous adenoma mean cancer?

No. VA does not mean cancer. However, all VAs are considered precancerous growths because they can turn into a type of colon cancer called adenocarcinoma over time.

What is the difference between a villous adenoma and a polyp?

In pathology, the term polyp is used to describe any growth that sticks out from the surface of a tissue. Because of the way they grow, TVAs are a type of polyp. However, not all polyps in the colon are TAs. Other types of polyps in the colon include tubular adenoma, tubulovillous adenoma, and sessile serrated lesions.

How is the diagnosis of villous adenoma made?

The diagnosis of VA is usually made after the adenoma is removed during a medical procedure called a colonoscopy. The adenoma may be removed in one piece or in multiple pieces. The tissue sample is then sent to a pathologist for examination under the microscope.

What does a villous adenoma look like under the microscope?

When examined under the microscope, the cells in the adenoma connect together to form long, thin finger-like projections called villi. The nuclei (the part of the cell that holds the genetic material) of the cells in the adenoma are also larger and hyperchromatic (darker) compared to the cells normally found on the inside surface of the colon.

What does dysplasia mean in a villous adenoma?

All VAs are made up of cells that show an abnormal pattern of growth called dysplasia. Dysplasia in the colon is important because it is considered a precancerous condition that if not treated can turn into a type of colon cancer called adenocarcinoma over time. When examining a VA, pathologists divide dysplasia into two categories: low-grade dysplasia and high-grade dysplasia. In order to make the diagnosis of VA, a pathologist must see at least low-grade dysplasia. High-grade dysplasia is less common, however, it is important because the risk of developing cancer is greater when high-grade dysplasia is seen in a VA.

What is a margin?

​In the colon, a margin is any tissue that was cut by the surgeon in order to remove the VA from your body. Dysplasia at the cut edge of the tissue means that the abnormal tissue may not have been completely removed from the body. Some VAs grow on a piece of tissue called a stalk and the adenoma is removed by cutting the stalk. In these cases, the margin is the part of the stalk that is cut. However, most VAs are removed and sent to pathology as multiple pieces (fragments) of tissue. In these cases, it may not be possible for your pathologist to determine which piece is the real margin and the changes seen at the margin will not be described in your report.

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