Colorectal polyps

Overview

•Abnormal mucosal growths projecting into the colonic lumen - most asymptomatic, discovered on screening or incidental colonoscopy

•Adenomatous polyps are the principal precursor of sporadic colorectal carcinoma via the adenoma-carcinoma sequence (10-15 years)

•Adenomatous polyps found in ~30-40% of adults over 50 at colonoscopy; slightly more common in men

Classification

Key polyp types
FeatureAdenomatous (neoplastic)Serrated/sessile serratedHamartomatous (e.g. Peutz-Jeghers)
Malignant potentialYes - main CRC precursorYes - 15-20% of CRCLow but increased GI cancer risk
PathwayAPC → KRAS → TP53BRAF mutation, CIMP, MLH1 silencing, MSI-highGermline STK11 mutation
MorphologyPedunculated or sessileFlat, right-sided - easily missedThroughout GI tract

Feature	Adenomatous (neoplastic)	Serrated/sessile serrated	Hamartomatous (e.g. Peutz-Jeghers)
Malignant potential	Yes - main CRC precursor	Yes - 15-20% of CRC	Low but increased GI cancer risk
Pathway	APC → KRAS → TP53	BRAF mutation, CIMP, MLH1 silencing, MSI-high	Germline STK11 mutation
Morphology	Pedunculated or sessile	Flat, right-sided - easily missed	Throughout GI tract

•Pedunculated (on a stalk) - lower malignant risk than sessile (flat/broad-based) lesions; stalk is a physical barrier to submucosal invasion

Presentation

•Asymptomatic - most common; found on NHS Bowel Cancer Screening (positive FIT test)

•Rectal bleeding - fresh or altered blood PR; more common with left-sided lesions

•Change in bowel habit - particularly with larger polyps

•Mucous discharge PR - classically villous adenomas of the rectum

•Secretory diarrhoea + hypokalaemia - large villous adenomas (McKittrick-Wheelock syndrome in extreme cases)

•Iron deficiency anaemia - chronic occult blood loss, especially right-sided lesions

Investigations

🏆 Gold standard

•colonoscopy - direct visualisation, biopsy, and polypectomy in the same sitting

•First-line screening: faecal immunochemical test (FIT) - NHS Bowel Cancer Screening Programme ages 50-74 in England; positive FIT triggers colonoscopy

•First-line bloods: FBC and iron studies - iron deficiency anaemia suggests chronic occult blood loss

🥈 Second-line

•CT colonoscopy (virtual colonoscopy) - when full colonoscopy contraindicated; cannot biopsy or remove

•Histopathology: all removed polyps sent for analysis - confirms type, degree of dysplasia, completeness of excision

•Genetics: if FAP or Lynch suspected - refer to regional genetics centre (APC gene for FAP; MLH1/MSH2/MSH6/PMS2 for Lynch)

⚠️
CEA is NOT used to diagnose polyps or screen for CRC - it is a tumour marker used to monitor response to treatment in established colorectal cancer only.

Management

🥇 First-line

•endoscopic polypectomy - pedunculated polyps by snare diathermy; sessile lesions by EMR or ESD for larger lesions

🥈 Second-line

•surgical resection - for polyps not amenable to endoscopic removal (very large sessile, confirmed invasive malignancy, difficult position)

Complications

•Malignant transformation to colorectal carcinoma - major long-term complication of untreated adenomas

•Post-polypectomy bleeding - immediate or delayed (up to 2 weeks); risk increases with larger polyps and EMR/ESD

•Colonic perforation - rare but serious complication of endoscopic removal, especially sessile lesions

•Intussusception - particularly with pedunculated polyps and Peutz-Jeghers hamartomas

•Electrolyte disturbance (hypokalaemia, hyponatraemia) - from secretory diarrhoea with large villous adenomas

Hereditary syndromes

FAP vs Lynch syndrome
FeatureFAPLynch syndrome (HNPCC)
GeneAPC (chromosome 5q21)MLH1, MSH2, MSH6, PMS2 (mismatch repair genes)
Polyp burdenHundreds to thousands from adolescenceFew polyps but accelerated progression
Lifetime CRC risk100% if untreated40-80%
ManagementProphylactic colectomy before age 25Colonoscopy every 1-2 years from age 25

Feature	FAP	Lynch syndrome (HNPCC)
Gene	APC (chromosome 5q21)	MLH1, MSH2, MSH6, PMS2 (mismatch repair genes)
Polyp burden	Hundreds to thousands from adolescence	Few polyps but accelerated progression
Lifetime CRC risk	100% if untreated	40-80%
Management	Prophylactic colectomy before age 25	Colonoscopy every 1-2 years from age 25

💡
Peutz-Jeghers syndrome: pathognomonic perioral/buccal/acral melanocytic macules + hamartomatous polyps throughout GI tract. Risk of intussusception from polyps.

Post-polypectomy surveillance (BSG risk stratification)

Surveillance intervals by risk
RiskCriteriaSurveillance
Low1-2 small tubular adenomas <10 mm, no high-grade dysplasiaReturn to routine NHS screening - no early surveillance
Intermediate3-4 small adenomas, or ≥1 adenoma 10-19 mmColonoscopy at 3 years
High≥5 adenomas, or any adenoma ≥20 mm, or high-grade dysplasiaColonoscopy at 1 year

Risk	Criteria	Surveillance
Low	1-2 small tubular adenomas <10 mm, no high-grade dysplasia	Return to routine NHS screening - no early surveillance
Intermediate	3-4 small adenomas, or ≥1 adenoma 10-19 mm	Colonoscopy at 3 years
High	≥5 adenomas, or any adenoma ≥20 mm, or high-grade dysplasia	Colonoscopy at 1 year

Hereditary syndrome management

•FAP: prophylactic total colectomy (ileorectal anastomosis or restorative proctocolectomy with ileal pouch) before age 25; sulindac or celecoxib may reduce polyp burden as a bridge but are not curative

•Lynch syndrome: colonoscopy every 1-2 years from age 25; prophylactic surgery considered individually after genetic counselling

•Peutz-Jeghers: two-yearly colonoscopic surveillance from age 25; polypectomy to prevent intussusception; refer to regional genetics centre