Colorectal Polyps
A colorectal polyp is a protrusion of tissue into the lumen above the surrounding mucosa. Usually asymptomatic, but may bleed, cause obstructive symptoms when large, or be a cancer precursor. Content below is from a textbook reference chapter (Sabiston Ch52 - Colorectal Neoplasia & Colon Cancer Surgery), not primary literature.
Classified endoscopically as pedunculated (with a stalk) or sessile (flat), and histologically (after excision/biopsy) as adenomas, hamartomas, inflammatory, serrated, etc. Main clinical importance: neoplastic polyps with CRC potential should be removed to reduce cancer risk.
Nonneoplastic polyps
- Hyperplastic polyps — small, sessile, usually <5 mm; elongated colonic crypts with a
papillary epithelial configuration, no atypia. Very common, frequently grossly indistinguishable
from small adenomas. No malignant potential (small, distal ones — see “serrated polyps” below for
the malignant-potential subset).
- Exception: small (<10 mm) hyperplastic polyps in the rectum or sigmoid specifically are considered low-risk with a 10-year surveillance interval (see surveillance table below) — consistent with their lack of malignant potential.
- Inflammatory polyps (pseudopolyps) — found in areas of healing inflammation (e.g. IBD — see Inflammatory Bowel Disease), formed after full-thickness epithelial ulceration in which new mucosa regenerates in an irregular polypoid configuration. No intrinsic neoplastic potential, but can be large and mimic a neoplasm; must be differentiated from true neoplastic lesions, particularly in diseased colons otherwise at risk for cancer (e.g. longstanding UC/Crohn’s).
- Hamartomas — uncommon GI polyps; can be sporadic or associated with a genetic syndrome (Peutz-Jeghers syndrome, juvenile polyposis syndrome, PTEN hamartoma syndrome — see Hamartomatous Polyposis Syndromes). No intrinsic malignant potential. Removal indicated for obstructive symptoms or bleeding.
Serrated polyps
Divided into three types: hyperplastic polyps (not precancerous — see above), sessile serrated polyps, and traditional serrated adenomas. The latter two combine adenomatous and hyperplastic features — colonic crypts with a saw-tooth serrated configuration plus nuclear atypia. Patients with sessile serrated polyps or traditional serrated adenomas have an increased CRC risk; CRC arising in these patients usually follows the serrated neoplasia pathway rather than the classic adenoma-carcinoma sequence (see Colorectal Cancer Molecular Pathways — this pathway corresponds to CIMP). These polyps should be removed, with patients followed by serial endoscopy.
Neoplastic polyps
All adenomas have malignant potential.
- Tubular adenomas — branched tubular glands; the most common type, 65–80% of polyps removed; frequently pedunculated.
- Villous adenomas — long, fingerlike projections of surface epithelium; 5–10% of adenomas; commonly sessile.
- Tubulovillous adenomas — elements of both; 10–25% of adenomas.
Malignancy risk increases with size (large), gross shape (sessile), histologic type (villous), and grade of dysplasia. An advanced adenoma — defined as ≥1 cm in size, high-grade dysplasia, or tubulovillous/villous histology — carries a significantly increased CRC risk. For example: <5% incidence of carcinoma in a tubular adenoma <1 cm, vs. a 50% chance a villous adenoma >2 cm contains a cancer.
Removal: adenomatous polyps found at colonoscopy should be excised. Pedunculated polyps are commonly removed with cold or hot snare polypectomy. Sessile polyps are frequently elevated from the underlying muscularis by saline injection, then excised with various techniques. Sessile polyps with a central depression that does not elevate adequately with saline injection (the “nonlifting sign”) are at increased risk both for perforation with endoscopic removal and for harboring neoplasia — commonly referred for surgical removal via segmental colectomy. Large polyps not removable endoscopically are also referred for surgery, though larger polyps can sometimes still be removed endoscopically with techniques such as endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD).
Malignant polyps
A malignant polyp is one where histologic examination after removal reveals a focus of carcinoma that has invaded through the muscularis mucosa. The key question: is complete endoscopic removal sufficient, or is further surgery (completion colectomy) needed?
- Carcinomas that do not pass the muscularis mucosa are “carcinoma in situ” and carry no metastatic risk.
- Carcinomas that do invade the muscularis mucosa carry a real risk of local recurrence and lymph node metastasis — depth of penetration is a key risk factor.
Haggitt classification (for pedunculated polyps):
| Level | Description |
|---|---|
| 0 | Carcinoma in situ, limited to the mucosa |
| 1 | Invading the submucosa, limited to the head of the polyp |
| 2 | Invading to the neck (junction of head and stalk) |
| 3 | Invading any part of the stalk |
| 4 | Invading the submucosa of the colon wall, below the level of the stalk but above the muscularis propria |
Sessile polyps with muscularis mucosa invasion are, by definition, Haggitt level 4. For these, the Kikuchi classification is used instead: Sm1 = invasion into the upper third of the submucosa, Sm2 = middle third, Sm3 = lower third.
Completion colectomy is commonly recommended for: pedunculated Haggitt level 4, sessile Kikuchi Sm2/Sm3, poor histologic differentiation, lymphovascular invasion, or incomplete removal/close resection margins. In these situations, risk of residual cancer and lymph node metastasis is higher than 10%.
Postpolypectomy surveillance
Finding an adenoma at colonoscopy is a risk factor for additional polyps.
| Index colonoscopy findings | Repeat colonoscopy |
|---|---|
| Small (<10 mm) hyperplastic polyps in rectum or sigmoid | 10 years |
| Low risk: 1–2 small tubular adenomas <10 mm, low-grade dysplasia | 5–10 years (AGA) / 10 years (ESGE) |
| High risk: villous histology, high-grade dysplasia, size ≥10 mm, or ≥3 polyps | 3 years |
| Piecemeal removal of a polyp | 6 months |
| Sessile serrated polyp <10 mm | 5 years |
| Sessile serrated polyp >10 mm, with dysplasia, or traditional serrated adenoma | 3 years |
Open items / gaps
- No primary trial data on EMR/ESD outcomes specifically, or on the comparative accuracy of the nonlifting sign.
- Hereditary polyposis syndromes (which change surveillance intervals dramatically) are covered separately — see Hereditary Colorectal Cancer Syndromes.