Villous Adenoma of the Colon and Rectum: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
August 23, 2026

A villous adenoma is a precancerous polyp that develops on the inner lining of the large intestine, including the colon and rectum. It is made up of abnormal glandular cells that grow in long, finger-shaped projections called villi, which resemble the normal lining of the small intestine. Villous adenomas are not cancer, but of the three conventional types of colon adenoma, they carry the highest risk of turning into a cancer called adenocarcinoma.

Villous adenomas are the least common of the three types. They tend to be larger than tubular adenomas by the time they are found, and they occur most often in the rectum and the lower part of the colon, where they may spread out flat across the lining rather than forming a rounded lump. This article explains what you may see in a pathology report after a villous adenoma is removed, what each finding means, and why this diagnosis requires closer follow-up than most polyps.

Is a villous adenoma cancer?

No. A villous adenoma is a precancerous polyp, not cancer. The abnormal cells inside it are confined to the surface lining of the bowel and have not grown down into the deeper tissue underneath. That downward growth, called invasion, is what separates a precancerous polyp from cancer.

Precancerous means the polyp could turn into cancer over time if it were not removed. Because villous adenomas are often large by the time they are found, they are more likely than other adenomas to already contain a small area of cancer somewhere within them, which is one reason the pathologist examines the entire specimen carefully rather than sampling part of it.

What causes a villous adenoma?

Villous adenomas develop when cells in the lining of the colon or rectum acquire mutations, which are errors in their DNA that allow the cells to grow in an abnormal, disorganized way. The earliest change usually affects a tumor suppressor gene called APC, which normally acts as a brake on cell division. When that brake is lost, the cells lining the bowel pile up and form a polyp. As the polyp grows, additional errors accumulate, and the villous growth pattern generally appears later in this process, which is why villous adenomas are usually larger and older than tubular adenomas when they are discovered.

Factors that increase the chance of developing a villous adenoma include:

Increasing age. Adenomas become steadily more common after age 45, which is why screening colonoscopy is offered from that age for people at average risk.
A personal or family history of colon polyps or colorectal cancer.
Inherited conditions that cause many polyps to form, such as familial adenomatous polyposis (FAP) and Lynch syndrome. These conditions account for only a small minority of adenomas.
Long-standing inflammatory bowel disease, including ulcerative colitis and Crohn’s disease.
Lifestyle factors, including smoking, heavy alcohol use, excess body weight, physical inactivity, and a diet high in red and processed meat and low in fiber.

What are the symptoms of a villous adenoma?

Many villous adenomas are found incidentally during a screening colonoscopy and cause no symptoms. Because these polyps are often large and often sit in the rectum, symptoms are more common than with other adenomas. They may include:

Blood in the stool or rectal bleeding.
Mucus in the stool. Villous adenomas produce mucus, and a large one in the rectum can release enough to be noticeable.
A change in bowel habits, such as diarrhea or constipation.
Abdominal cramping or discomfort.
A feeling of needing to pass stool that does not resolve when the polyp sits low in the rectum.

Rarely, a very large villous adenoma in the rectum releases so much fluid and salt that it causes profuse watery diarrhea, dehydration, low potassium, and kidney problems. This is called McKittrick-Wheelock syndrome. It is uncommon, and removing the polyp resolves it.

None of these symptoms can tell you whether a polyp is present, since many other conditions cause them. Only examination of the bowel and microscopic examination of the tissue removed can do that.

How is the diagnosis made?

Doctors diagnose a villous adenoma only after removing the polyp and examining it under a microscope. During a colonoscopy, a doctor removes small polyps with a procedure called a polypectomy, in which a wire loop is passed through the scope to remove the growth. Villous adenomas are often too large or too flat for a simple polypectomy, so doctors more often remove them with endoscopic mucosal resection or endoscopic submucosal dissection, techniques that lift and remove a wider area of the lining. A large villous adenoma low in the rectum is sometimes removed through the anus in a separate operation instead.

The tissue is then sent to a pathology laboratory, where a pathologist examines it under a microscope. In a villous adenoma, the surface is thrown into tall, finger-shaped fronds, each with a thin core of supporting tissue and covered by abnormal glandular cells with darker, more crowded nuclei than the surrounding normal colonic mucosa. These abnormal changes are called dysplasia, and by definition every adenoma shows dysplasia.

The pathologist also examines the base of the specimen carefully to confirm that no abnormal cells have grown into the deeper tissue. This step matters more for a villous adenoma than for a small polyp, because the chance of finding an unsuspected focus of cancer within the specimen is higher. Since a villous adenoma is not itself cancer, no imaging scans are needed when the examination shows no invasion.

Growth pattern

The words tubular, tubulovillous, and villous describe the shape of the glands the pathologist sees in the polyp, and they divide colon and rectal adenomas into three types. Most adenomas contain some of both shapes, so the diagnosis depends on the proportion of villous growth:

Tubular adenoma. Less than 25% villous growth. This is the most common type and carries the lowest risk of progressing to cancer.
Tubulovillous adenoma. Between 25% and 75% villous growth.
Villous adenoma. More than 75% villous growth. This is the diagnosis described in this article, the least common of the three, and the one that carries the highest risk.

Estimating the proportion of villous growth involves judgment rather than measurement, and two pathologists reviewing the same polyp will not always place it in the same category, particularly near the 75% boundary. A polyp reported elsewhere as tubulovillous rather than villous would be managed the same way, since any villous component places a polyp in the higher risk group.

Dysplasia

Every villous adenoma shows dysplasia, a word pathologists use for cells that look abnormal under the microscope but are not yet cancer. The report will describe the dysplasia as one of two grades.

Low grade dysplasia. The cells look mildly abnormal. Their nuclei are enlarged, darker, and more crowded than normal, but the glands keep their usual orderly arrangement. This is still the most common finding in a villous adenoma.
High grade dysplasia. The cells look markedly abnormal, with large, irregular nuclei and prominent nucleoli, and the glands lose their orderly arrangement and crowd together. High grade dysplasia is still not cancer, but it sits closer to cancer along the same pathway.

High grade dysplasia is found more often in villous adenomas than in the other two types, because villous growth, large size, and high grade dysplasia all tend to develop as a polyp becomes older. In a large polyp, dysplasia is often uneven, with high grade change present in only one part. The report describes the highest grade found anywhere in the specimen, so high grade dysplasia does not mean the whole polyp looked that way.

Size and number of polyps

Two other findings recorded after a villous adenoma is removed are the polyp’s size and the total number of polyps found. Both influence how soon the next colonoscopy is recommended.

Size is usually reported in millimeters. The most important follow-up threshold is 10 mm, and a second threshold at 20 mm affects how the removal site is checked afterward. Most villous adenomas exceed 10 mm. You may notice that the size in the pathology report differs from the size your endoscopist described, particularly for a flat lesion removed in pieces, since the fragments cannot be reassembled to their original dimensions in the laboratory. In that case, the endoscopist’s measurement is more reliable.

The total number of adenomas removed also matters. Finding three or more, and particularly finding ten or more, places you in a higher risk group and may prompt your doctor to consider testing for an inherited polyp condition.

Margins

The margin is the cut edge of the tissue removed during the procedure. The pathologist examines it to judge whether the whole villous adenoma was taken out. Your report will describe the margin in one of three ways:

Negative (clear) margin. No abnormal cells are seen at the cut edge. The polyp appears to have been removed completely.
Positive margin. Abnormal cells reach the cut edge, so some polyp tissue may remain in the bowel. Your doctor will usually arrange a repeat examination of that area.
Cannot be assessed. Larger polyps are often removed in several pieces, and the edges of the tissue are frequently sealed with heat during removal, leaving a cautery artifact. Either situation can make the margin impossible to evaluate reliably.

An unassessable margin is the most common result for a villous adenoma, because these polyps are large and flat and are usually removed in fragments. This is expected, not a sign that something went wrong, but it does mean the removal site must be inspected again later to confirm nothing remains. Residual tissue is the usual reason a villous adenoma appears to come back in the same spot.

Advanced adenoma

Your doctor may describe a villous adenoma as an advanced adenoma. This is not a separate diagnosis but a risk category that gathers together several findings. An adenoma is called advanced if it has any one of the following features:

A villous component, meaning the polyp is a tubulovillous or villous adenoma.
A size of 10 mm or larger.
High grade dysplasia.

Because a villous growth pattern is one of the three criteria, every villous adenoma is an advanced adenoma, whatever its size and whatever the grade of dysplasia. Most villous adenomas meet two or three of the criteria at once. This is why your next colonoscopy will be recommended sooner than it would be for a small tubular adenoma.

What is the risk that a villous adenoma will become cancer?

Villous adenomas carry the highest risk of progressing to colorectal adenocarcinoma of the three conventional adenoma types. Even so, most are removed before that happens. The change from adenoma to cancer is slow, typically taking a decade or more, and removing the polyp interrupts the process.

The more immediate question for a large villous adenoma is not whether it will become cancer in the future but whether a small area of cancer is already present within it. That possibility rises with the size of the polyp and with high grade dysplasia, and it is why the entire specimen is examined rather than a sample of it. If the examination finds no invasion, the polyp is precancerous and the risk of leaving cancer behind is low.

Two related terms sometimes appear on reports for large adenomas and can be confusing. Intramucosal carcinoma means abnormal cells have moved into the lamina propria, a thin supporting layer just below the surface lining, but no further. In the colon this does not behave like invasive cancer and is generally cured by removing the polyp. A malignant polyp is different: it means cancer has grown through into the deeper layer of the bowel wall and can potentially spread. If either term appears on your report, the diagnosis is no longer a simple villous adenoma, and your doctor will discuss what it means for you.

What happens after this diagnosis?

For a villous adenoma with no invasion, removing the polyp is the whole treatment. No chemotherapy or radiation is involved. When a large rectal villous adenoma cannot be removed completely through the scope, a transanal operation to excise the remaining tissue may be considered, and this is a decision your gastroenterologist and a colorectal surgeon would make together based on the size, the location, and what the pathology showed.

The rest of the plan is about when to look again. Your doctor sets that interval using the findings in your report, along with your age, general health, and family history. Current guidelines from the US Multi-Society Task Force on Colorectal Cancer group findings roughly as follows:

A villous adenoma, completely removed. The next colonoscopy is generally considered at 3 years, because any adenoma with a villous component counts as an advanced adenoma.
A villous adenoma with high grade dysplasia, or 10 mm or larger. Also generally 3 years, since these features place the polyp in the same category rather than a separate one.
A polyp 20 mm or larger removed in pieces. A repeat examination of that specific area is usually arranged within 6 months, separately from the routine schedule above, to confirm the site is clear. A further check is often done after that before returning to the routine interval.
More than ten adenomas in total. Generally within 1 year, along with consideration of testing for an inherited polyp condition.

These intervals are a starting point rather than a rule, and the quality of the examination itself matters. If the bowel preparation was poor or the colonoscopy could not be completed, your doctor may recommend repeating it sooner regardless of what the polyp showed. Your pathology report is one of several factors your doctor weighs when setting the plan, and it also describes what happens after your pathology report.

Having one adenoma removed does not mean more will form, but it does place you at somewhat higher risk than someone who has never had one, which is why ongoing surveillance is recommended rather than a return to routine screening.

Questions to ask your doctor

Where in the colon or rectum was the polyp found?
How large was the polyp, and how many polyps were removed in total?
Was the polyp removed in one piece or in fragments?
What did the margin show, and does it mean any tissue was left behind?
Did my report describe low grade or high grade dysplasia?
Did the pathologist find any area of cancer within the polyp?
Do I need a separate follow-up look at the site where the polyp was removed, and when?
Since a villous adenoma counts as an advanced adenoma, when should my next colonoscopy be?
Is any further procedure needed to remove tissue that could not be taken out during the colonoscopy?
Was the bowel preparation good enough for a complete examination?
Does this finding change my overall risk of colorectal cancer?
Should my children, siblings, or parents start screening earlier than usual?
Is there anything in my history that suggests I should be tested for an inherited polyp condition?
Are there changes to my diet, weight, alcohol use, or smoking that would lower my risk of new polyps?