Tubulovillous adenoma of the colon and rectum

by Ipshita Kak MD FRCPC
April 5, 2022


What is a tubulovillous adenoma?

A tubulovillous adenoma 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 tubulovillous adenomas are associated with an increased risk of developing a type of colon cancer called adenocarcinoma over time.

How do pathologists make the diagnosis of tubulovillous adenoma?

The diagnosis of tubulovillous adenoma 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 tubulovillous adenoma look like under the microscope?

When examined under the microscope, the tumour cells in parts of the adenoma connect together to form long, thin finger-like projections called villi. In other areas, the tumour cells connect together to form tube-shaped glands. The nuclei (the part of the cell that holds the genetic material) of the tumour cells 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 tubulovillous adenoma?

All tubulovillous adenomas 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 cancer called adenocarcinoma over time.

When examining a tubulovillous adenoma, pathologists divide dysplasia into two categories: low-grade dysplasia and high-grade dysplasia. In order to make the diagnosis of tubulovillous adenoma, 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 tubulovillous adenoma.

What is a margin?

​In the colon, a margin is any tissue that was cut by the surgeon in order to remove the tubulovillous adenoma 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 tubulovillous adenomas 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 tubulovillous adenomas 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.

Margin

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