Colorectal adenomas (polyps)

Definition

An intestinal polyp is any mass of tissue arising from the bowel wall and protruding into the lumen. Polyps may be sessile or pedunculated and vary considerably in size. Adenomatous (neoplastic) polyps are of particular importance because most colon cancers arise in a previously benign adenoma.

Classification

• Adenomatous (neoplastic) polyps: tubular, tubulovillous and villous adenomas
• Advanced adenomas: adenomas of 10 mm or more, or with a villous component or high-grade dysplasia; they carry a higher risk of progression to cancer
• Non-adenomatous (non-neoplastic) polyps: hyperplastic polyps, hamartomas (e.g. in Peutz-Jeghers syndrome), juvenile polyps, inflammatory pseudopolyps, lipomas, leiomyomas and rarer tumors
• By shape: sessile or pedunculated

Occurrence & epidemiology

In colonoscopy studies, adenomas are found in 20–53% of people aged 50 or older and advanced adenomas in up to 9.7%. Polyps – often multiple – are most common in the rectum and sigmoid and decrease in frequency toward the cecum. The proportion of polyps that already contain cancer ranges from 0.2 to 5%. Advanced adenomas are estimated to progress to cancer at about 1–5% per year, at the lower end in women and at the higher end in older age groups.

Aetiopathogenesis

Most colorectal cancers arise through malignant transformation within adenomatous polyps. Numerous polyps may indicate familial adenomatous polyposis or its attenuated variant; multiple juvenile polyps (but not single sporadic ones) are associated with an increased cancer risk. Juvenile polyps occur in children, outgrow their blood supply and usually autoamputate during or after puberty. Inflammatory polyps and pseudopolyps occur in ulcerative colitis and Crohn's disease of the colon.

Clinical features

Most polyps cause no symptoms. The most common complaint is rectal bleeding, usually occult and only rarely massive. Large polyps can cause cramps, abdominal pain or bowel obstruction. Rectal polyps are sometimes palpable on digital examination; a polyp on a long pedicle may occasionally prolapse through the anus. Large villous adenomas can rarely cause watery diarrhea with hypokalemia.

Diagnosis

• Colonoscopy: the usual method for detecting polyps; all polyps found are examined histologically for cancer
• Because rectal polyps are often multiple and may coexist with cancer, the entire colon up to the cecum is examined even if a lesion is found at sigmoidoscopy
• Barium enema (especially double-contrast): can show polyps but is inferior to colonoscopy
• Digital rectal examination: palpable rectal polyps
• Stool tests for occult blood may be positive due to bleeding polyps

Keep learning in the app

Further reading (open access)

1. MSD Manual Professional: Polyps of the Colon and Rectum
2. MSD Manual Professional: Colorectal Cancer
3. StatPearls: Colorectal Polyps and Polyposis Syndromes

Cross-references