Villous adenoma of the colon

by Jason Wasserman MD PhD FRCPC
January 17, 2024


A villous adenoma is a precancerous growth that arises from the cells that cover the inside of the colon. It is a common type of polyp in the colon. It is considered a precancerous growth because it can evolve into a type of colon cancer called invasive adenocarcinoma over time.

How is this diagnosis made?

The diagnosis of villous adenoma can only be made after part, or all of the adenoma is removed and the tissue is examined under the microscope by a pathologist. The adenoma may be removed in one piece or multiple pieces.

What does a villous adenoma look like under the microscope?

Under microscopic examination, a villous adenoma is made up of long finger-like projections of tissue 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.

Low versus high grade dysplasia in a villous adenoma

All villous adenomas show an abnormal pattern of growth called dysplasia. Dysplasia is important because it is a precancerous change that can become cancerous over time. When examining a villous adenoma, pathologists divide dysplasia into two levels: low grade dysplasia and high grade dysplasia.

Low grade dysplasia

Low grade dysplasia is an early precancerous change seen in most villous adenomas. If left untreated, low grade dysplasia can change into high grade dysplasia or cancer over time. However, the overall risk is low.

High grade dysplasia

High grade dysplasia is a more advanced precancerous change seen in a small number of villous adenomas. If left untreated, villous adenomas with high grade dysplasia can turn into a type of colon cancer called invasive adenocarcinoma. If possible, all villous adenomas with high grade dysplasia should be removed completely.

​Margins

A margin is any tissue that was cut by the surgeon to remove the villous 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 villous 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 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.

A+ A A-