Colorectal Polyps

Expansion

Neoplastic (adenomatous), with malignant potential

• Tubular adenoma - the commonest, usually pedunculated, lowest risk
• Tubulovillous
• Villous adenoma - sessile, highest risk, and large ones can cause a secretory diarrhoea with hypokalaemia
• Sessile serrated lesions - flat, right sided, easily missed, progressing by the serrated (microsatellite instability) pathway

Non-neoplastic

• Hyperplastic - the commonest polyp overall, small, left sided, no malignant potential
• Inflammatory (pseudopolyps) - in inflammatory bowel disease
• Hamartomatous - Peutz-Jeghers, juvenile polyps

Three features raise risk: size over 1 cm, villous architecture, and high grade dysplasia.

Polyposis syndromes

• Familial adenomatous polyposis: APC mutation, autosomal dominant, hundreds of adenomas, 100 per cent lifetime cancer risk, requiring prophylactic colectomy. Gardner’s variant adds osteomas and desmoid tumours
• Lynch syndrome (HNPCC): mismatch repair mutation, few polyps but rapid progression, right sided, with endometrial and other cancers
• Peutz-Jeghers: hamartomas with perioral pigmentation, causing intussusception, with increased cancer risk