ConditionDigestive system
Villous Adenoma
A villous adenoma is a type of precancerous polyp (adenoma) in the colon or rectum, named for its finger-like, frond-shaped growth pattern under the microscope. It is less common than other adenomas but more likely to turn into colorectal cancer, especially when large. Most cause no symptoms and are found during screening colonoscopy. Large ones can bleed or, rarely, cause watery diarrhea with mucus and low potassium. Removing the whole polyp and keeping up with follow-up colonoscopies prevents most cancers.
Also called: Villous polyp, villous colon polyp, tubulovillous adenoma (mixed type), advanced adenoma
At a glance
- What it is
- A precancerous colon or rectal polyp with a villous (frond-like) structure.
- Types
- Villous (more than 75 percent villous) and tubulovillous (25 to 75 percent).
- Cancer risk
- Higher than tubular adenomas, rising with size and dysplasia.
- Symptoms
- Usually none. Sometimes bleeding, mucus, watery diarrhea or low potassium.
- Treatment
- Complete removal during colonoscopy or by surgery, then surveillance colonoscopy.
When to get help
Call 911 or go to the ER
- Heavy rectal bleeding, passing large clots, or bleeding with dizziness or fainting
- Severe weakness, muscle cramps or palpitations with persistent watery diarrhea (possible very low potassium)
See a doctor within a day or two
- Ongoing rectal bleeding or black stools
- Large volumes of watery or mucus-filled diarrhea lasting more than a few days
Book a routine appointment
- A change in bowel habits lasting more than a few weeks
- Unexplained tiredness or iron deficiency anemia
- Age 45 or older and not yet screened for colorectal cancer, or due for a follow-up colonoscopy after polyp removal
What a villous adenoma is
Adenomas are growths of the glandular lining of the colon and rectum. Pathologists classify them by their structure under the microscope:
| Type | Structure | Share of adenomas | Cancer potential |
|---|---|---|---|
| Tubular adenoma | Mostly tube-shaped glands | Most common | Lowest |
| Tubulovillous adenoma | 25 to 75 percent villous | Common | Intermediate |
| Villous adenoma | More than 75 percent villous | Least common | Highest |
Villous adenomas are often flat or carpet-like, broad-based (sessile) and large, and are frequently found in the rectum.
What makes an adenoma "advanced"
An adenoma is called advanced if it is 10 mm or larger, has villous features, or has high-grade dysplasia (very abnormal cells). Advanced adenomas carry a higher risk of cancer and need closer follow-up.
Symptoms
Most villous adenomas cause no symptoms. When present, symptoms include:
- rectal bleeding or blood in the stool
- mucus in the stool
- a change in bowel habits
- iron deficiency anemia from slow, hidden bleeding, causing tiredness
- a feeling of incomplete emptying, with rectal polyps
McKittrick-Wheelock syndrome
Rarely, a large villous adenoma in the rectum secretes large amounts of fluid and salt, causing profuse watery, mucus-rich diarrhea, dehydration, very low potassium (hypokalemia), low sodium and kidney injury. Removing the polyp cures it.
Causes and risk factors
- age 45 and older
- family history of colorectal cancer or advanced adenomas
- inherited syndromes: familial adenomatous polyposis and Lynch syndrome
- lifestyle: smoking, obesity, heavy alcohol use, high intake of red and processed meat, low physical activity
- inflammatory bowel disease involving the colon
- type 2 diabetes
Diagnosis
- colonoscopy: the main way villous adenomas are found and removed
- stool tests (FIT or stool DNA tests) and CT colonography can detect larger polyps and lead to colonoscopy
- biopsy and pathology: determine the type, the degree of dysplasia and whether any cancer is present
- endoscopic ultrasound or MRI for large rectal adenomas to check depth before removal
Treatment
Removal during colonoscopy
- polypectomy: smaller polyps are removed with a wire snare
- endoscopic mucosal resection (EMR): fluid is injected under a large flat polyp to lift it, then it is removed, sometimes in pieces
- endoscopic submucosal dissection (ESD): removes large polyps in one piece, in specialist centers
The area may be marked with ink (tattooed) so it can be found again.
Surgery
Surgery is used when a polyp cannot be removed safely by endoscopy, when cancer is found that has invaded deeply, or when removal was incomplete. Rectal polyps may be removed through the anus (transanal surgery).
Follow-up colonoscopy
Follow-up depends on what was found. Under the 2020 US Multi-Society Task Force guidance:
- after removal of an adenoma with villous features or high-grade dysplasia, or 10 mm or larger: repeat colonoscopy in 3 years
- after piecemeal removal of a polyp 20 mm or larger: repeat in 6 months to check for leftover tissue
- intervals may differ with family history, number of polyps or inherited syndromes
Outlook
Complete removal of a villous adenoma greatly reduces the risk of colorectal cancer. Large adenomas can recur at the removal site, which is why follow-up matters. If cancer is found within the polyp, further treatment depends on how deeply it has spread.
Prevention
- screening from age 45 for people at average risk, or earlier with a family history
- staying active, maintaining a healthy weight, not smoking and limiting alcohol and processed meat
- eating plenty of fiber from vegetables, fruit, legumes and whole grains
Frequently asked questions
Is a villous adenoma cancer?
No, it is a precancerous polyp. However, it has a higher chance of developing into cancer than other adenomas, especially when large or with high-grade dysplasia. Sometimes a small area of cancer is found within it, which the pathology report will state.
What is the difference between a tubular and villous adenoma?
They are described by their structure. Tubular adenomas have mostly tube-shaped glands and are the most common, with lower cancer risk. Villous adenomas have finger-like projections, are less common, often larger, and have higher cancer risk. Tubulovillous adenomas are mixed.
What happens after a villous adenoma is removed?
You will usually need a follow-up colonoscopy in 3 years, or in 6 months if a large polyp was removed in pieces. Your doctor will set the interval based on the size, number and pathology of the polyps.
Can villous adenomas cause symptoms?
Usually not, but large ones can cause rectal bleeding, mucus in the stool, a change in bowel habits or anemia. Rarely, a large rectal villous adenoma causes severe watery diarrhea and low potassium.
Sources
This guide was written from current patient and clinical guidance, including:
- US Multi-Society Task Force on Colorectal Cancer: Recommendations for Follow-Up After Colonoscopy and Polypectomy (2020)
- American Cancer Society: Understanding your pathology report, colon polyps
- US Preventive Services Task Force: Colorectal Cancer Screening (2021)
- NIDDK: Colon Polyps
- American Society for Gastrointestinal Endoscopy: Polyp removal patient information