Colorectal Polyps

What are colorectal polyps?

Colorectal polyps are growths that develop on the inner lining of the colon or rectum. They occur when the normal process of cell growth and repair becomes disrupted, leading to the formation of tissue projections into the bowel. Polyps vary in size and shape; some are small and flat, while others grow on a stalk like a mushroom.

Most polyps are benign (non-cancerous) at the time they are detected. However, certain types, particularly adenomatous polyps (adenomas), have the potential to develop into colorectal cancer if left untreated. 

Polyps may not cause any noticeable symptoms, especially when they are small. In some cases, larger polyps can lead to rectal bleeding, changes in bowel habits, abdominal discomfort, or anaemia due to chronic blood loss. Because they often remain silent, colorectal polyps are most commonly identified during routine screening procedures such as colonoscopy.

Detecting and removing colorectal polyps is an important step in preventing colorectal cancer, which is why regular screening is strongly recommended, especially for individuals over 50 or those with a family history of the disease.

Types of colorectal polyps

Colorectal polyps are classified according to their appearance under the microscope and their potential to become cancerous. The main types include:

• Adenomatous polyps (adenomas) — these are the most common type and are considered precancerous. Although not all adenomas develop into cancer, most colorectal cancers begin as adenomatous polyps. They can be tubular, villous, or tubulovillous in structure, with villous adenomas carrying a higher risk of malignancy.

• Hyperplastic polyps — usually small and located in the rectum or sigmoid colon, these polyps are generally benign and rarely progress to cancer. However, larger hyperplastic polyps, particularly those on the right side of the colon, may sometimes need closer evaluation.

• Sessile serrated lesions (SSLs) — these flat or slightly raised polyps share features of hyperplastic polyps but have a greater potential to turn into cancer through what is called the “serrated pathway.” Because they are harder to detect during colonoscopy, SSLs are closely monitored when found.

• Inflammatory polyps — often seen in people with chronic inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease, these polyps themselves do not usually become cancerous. However, their presence indicates an underlying condition that increases the overall risk of colorectal cancer.

• Hamartomatous polyps — these are less common and are often associated with inherited conditions like Peutz-Jeghers syndrome or juvenile polyposis. While individual hamartomas are usually benign, patients with these syndromes face a higher lifetime risk of colorectal and other cancers.

What causes colorectal polyps?

Colorectal polyps develop when the normal cell growth and repair process in the colon or rectum is disrupted. Instead of shedding and regenerating in a controlled way, cells begin to grow excessively, forming tissue projections along the bowel lining. This abnormal growth is driven by specific cellular and genetic changes.

The main causes include:

• Genetic mutations — changes in genes that regulate cell growth can trigger uncontrolled cell division. Mutations in tumour suppressor genes or oncogenes often underlie the development of adenomas and other precancerous polyps.

• Adenoma–carcinoma sequence — many adenomatous polyps form through a stepwise process in which progressive genetic changes transform normal glandular cells into abnormal tissue with the potential to become cancerous.

• Serrated pathway changes — sessile serrated lesions and some hyperplastic polyps arise from errors in DNA replication and repair, which allows abnormal cells to survive and multiply.

• Inherited conditions — syndromes such as familial adenomatous polyposis (FAP) or MUTYH-associated polyposis (MAP) are caused by inherited gene defects that lead to the formation of multiple polyps throughout the colon.

• Chronic inflammation — inflammatory bowel diseases, such as ulcerative colitis or Crohn’s disease, disrupt normal cell regeneration, sometimes leading to inflammatory polyps.

What are the signs and symptoms of colorectal polyps?

Colorectal polyps often do not cause any symptoms, especially when they are small. Many are discovered incidentally during a routine screening colonoscopy. However, when symptoms occur, they may signal the presence of larger or multiple polyps.

Possible signs and symptoms include:

• Rectal bleeding — blood may appear on toilet paper, in the stool, or in the toilet bowl after a bowel movement.

• Changes in stool colour — stools may appear black or dark due to bleeding higher in the colon.

• Altered bowel habits — persistent constipation, diarrhoea, or narrowing of the stool may occur if polyps obstruct part of the bowel.
• Passage of mucus in the stools

• Abdominal discomfort — cramping, bloating, or pain may develop with larger polyps.

• Iron deficiency anaemia — slow, chronic blood loss from polyps can lead to fatigue, weakness, and shortness of breath.

Because many colorectal polyps are silent, regular screening is important to detect and remove them before they cause problems or progress to colorectal cancer.

What are the complications of colorectal polyps? 

Although many colorectal polyps are harmless when detected early and removed, some can lead to complications if left untreated.

Possible complications include:

• Colorectal cancer — certain types of polyps, particularly adenomas and sessile serrated lesions, can undergo gradual genetic changes and develop into colorectal cancer over time.

• Bleeding — polyps may cause bleeding within the bowel, leading to visible blood in the stool or hidden blood that results in iron deficiency anaemia.

• Bowel obstruction — very large polyps can narrow the colon and interfere with normal bowel movements, sometimes causing constipation or abdominal pain.

• Recurrence — even after removal, some people may develop new polyps in other areas of the colon, which is why ongoing surveillance is recommended.

Who is at risk of colorectal polyps in Singapore?

Anyone can develop colorectal polyps, but certain people are more likely to have them because of age, family history, or medical conditions. Understanding these risk groups highlights the importance of regular screening.

You may be at higher risk if you have:

• Older age — the likelihood of developing colorectal polyps increases after age 50.

• Family history — having a close relative with colorectal polyps or colorectal cancer raises your risk.

• Inherited syndromes — conditions such as familial adenomatous polyposis (FAP), MUTYH-associated polyposis (MAP), or Lynch syndrome strongly predispose to multiple polyps and cancer.

• Inflammatory bowel disease — long-term ulcerative colitis or Crohn’s disease can promote the development of inflammatory polyps and increase cancer risk.

• Personal history of polyps — if you have had colorectal polyps before, new ones are more likely to form in the future.

How are colorectal polyps diagnosed? 

Colorectal polyps are often silent and may not cause noticeable symptoms, which is why they are usually detected through screening tests. Diagnosis involves visualising the inside of the colon and rectum to identify and remove polyps for examination.

Common diagnostic methods include:

• Colonoscopy — colonoscopy is the most commonly used test for detecting colorectal polyps. A flexible tube with a camera is inserted into the colon, which allows the doctor to see the entire bowel lining and remove any polyps found during the procedure.

• Flexible sigmoidoscopy — similar to colonoscopy but examines only the rectum and lower part of the colon. Polyps in this region can be detected and removed, though it does not assess the whole colon.

• CT colonography (virtual colonoscopy) — a specialised CT scan that produces detailed images of the colon and rectum. If polyps are detected, a follow-up colonoscopy is required for removal.

• Stool-based tests — tests such as the faecal immunochemical test (FIT), faecal occult blood test (FOBT), or stool DNA test can detect hidden blood or abnormal DNA shed by polyps. A positive result usually leads to a colonoscopy for confirmation and treatment.

Because many polyps do not cause symptoms, routine screening is the most reliable way to detect them early and prevent colorectal cancer.

What are the treatment options for colorectal polyps? 

Colorectal polyps are usually removed once they are detected, most often during a colonoscopy. The goal of treatment is to prevent progression into colorectal cancer and to monitor for recurrence.

• Polyp removal (polypectomy) — most polyps can be removed endoscopically at the time of colonoscopy. Several techniques are used depending on the type, size, and shape of the polyp:

• Forceps polypectomy  —  small polyps (generally <5 mm) can be removed using biopsy forceps. However, this method may not always retrieve the entire lesion, so larger polyps are better managed with other techniques.

• Snare polypectomy  —  a wire loop (snare) is used to encircle and remove polyps. In cold snare polypectomy, the polyp is cut off without cautery, which reduces risk of complications. In hot snare polypectomy, electrocautery is applied to cut and cauterise the tissue, useful for larger or stalked (pedunculated) polyps.

• Endoscopic mucosal resection (EMR) / Endoscopic submucosal dissection (ESD)  —  These advanced techniques are used for larger, flat, or sessile polyps. EMR involves injecting fluid under the polyp to lift and remove it. ESD, more technically demanding, allows en bloc removal of larger or high-risk polyps, including a small rim of surrounding tissue, reducing recurrence risk.

• Surgery — surgical removal may be required if:

• Polyps are too large, flat, or numerous to be safely removed endoscopically.

• There are inherited syndromes such as familial adenomatous polyposis (FAP) or MUTYH-associated polyposis (MAP), which carry a very high risk of colorectal cancer.

• Cancer is found within a polyp or cannot be excluded.
  • Colectomy  — Removal of part or all of the colon.
  • Proctocolectomy  —  removal of the entire colon and rectum. Patients usually require reconstruction with an ileal pouch–anal anastomosis (IPAA) or a permanent ileostomy.

• Observation — after removal, follow-up colonoscopy is essential. The timing depends on the number, size, and histology of the polyps:

• For low-risk adenomas, repeat colonoscopy is typically recommended within 5–10 years.
• For high-risk adenomas (large size, villous features, high-grade dysplasia), surveillance may be advised every 3 years.

In inherited syndromes, screening is more frequent, often annually.

Summary 

Colorectal polyps are growths that form on the inner lining of the colon or rectum due to abnormal cell growth. Most are harmless at first, but certain types, such as adenomas and sessile serrated lesions, can develop into colorectal cancer if left untreated. They often cause no symptoms, though larger polyps may lead to rectal bleeding, changes in bowel habits, abdominal discomfort, or anaemia.

Diagnosis is usually made during screening procedures, most commonly colonoscopy, which also allows removal of polyps at the same time. Other tests such as sigmoidoscopy, CT colonography, or stool-based tests may also be used. Treatment typically involves endoscopic polypectomy, with advanced methods like EMR or ESD used for larger or flat lesions. Surgery is reserved for polyps that are too large, cancerous, or linked to inherited syndromes. Regular follow-up is essential since new polyps can develop even after removal. 

If you are concerned about your risk or are due for screening, schedule a consultation with Tan Siong San Surgery for a detailed evaluation, tailored treatment, and long-term prevention of colorectal cancer.

Frequently Asked Questions (FAQs)