Villous adenoma of the colon

What is a villous adenoma?

A villous adenoma is a non-cancerous growth in the colon. It develops from the glands in the mucosa on the inside surface of the colon. These adenomas can develop anywhere along the length of the colon from the cecum to the rectum. All villous adenomas are associated with an increased risk for developing a type of colon cancer called adenocarcinoma over time.

The colon

The colon is a part of the gastrointestinal tract which also includes the mouth, esophagus, stomach, small bowel, and anus. The colon is a long hollow tube that starts at the small bowel and ends at the anal canal. The colon is divided into sections which include the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. The functions of the colon are to absorb water from the food that we eat and to move waste out of the body.

The colon is made up of six layers of tissue:

  1. Mucosa – The mucosa is the tissue that lines the inside surface of the colon. The mucosa includes epithelial cells that form structures called glands. The glands are surrounded and supported by a tissue called lamina propria.
  2. Muscularis mucosa – This is a thin layer of muscle that sits just below the mucosa.
  3. Submucosa – The submucosa contains many thick blood vessels and lymphatic channels.
  4. Muscularis propria – The muscularis propria is a thick bundle of muscle. The muscles in the muscularis propria help move digested food and waste along the colon.
  5. Subserosal adipose tissue – This is a layer of fat that sits directly below the muscularis propria. The subserosal adipose tissue is near the outside surface of the colon.
  6. Serosa – The serosa is a thin layer of tissue that covers the subserosal adipose tissue and the outside of the colon.
normal colon layers

 

How do pathologists make this diagnosis?

The diagnosis of villous 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.

Dysplasia in a villous adenoma

When examined under the microscope, villous adenomas are made up of cells that show an abnormal pattern of growth. Pathologists call this abnormal pattern of growth dysplasia. Dysplasia in the colon is important because it is considered a precancerous condition that can turn into cancer over time.

In the colon, pathologists divide dysplasia into two categories: low-grade dysplasia and high-grade dysplasia. All villous adenomas show at least low-grade dysplasia. Your pathologist will carefully examine your tissue sample to look for any high-grade dysplasia because the risk for developing cancer is greater with high-grade dysplasia.

Margins

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

Margin

Dysplasia at the cut edge of the tissue means that the abnormal tissue may not have been completely removed from the body.

Villous adenomas are often removed and sent to pathology as multiple pieces (fragments) of tissue. In some of these cases, it will 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.

by Ipshita Kak MD FRCPC (updated July 24, 2021)
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