Paper II
Question
Intestinal polyps: classification and syndromes
Answer
Intestinal polyps are mucosal outgrowths of the bowel wall, classified as:
1. Non-neoplastic polyps:
- Hyperplastic polyps — most common non-neoplastic type, small, serrated glandular architecture, minimal malignant potential.
- Hamartomatous polyps — disorganized overgrowth of normal tissue elements; seen in juvenile polyps and Peutz-Jeghers polyps.
- Inflammatory polyps — arise in the setting of chronic mucosal inflammation (e.g., inflammatory bowel disease “pseudopolyps”).
2. Neoplastic polyps (adenomas):
- Tubular adenoma — most common; predominantly tubular glands; lowest malignant potential of the adenoma subtypes.
- Villous adenoma — finger-like villous projections; highest malignant potential.
- Tubulovillous adenoma — mixed pattern; intermediate risk.
- Malignant potential correlates with size, villous component, and degree of dysplasia.
Polyposis syndromes:
- Familial Adenomatous Polyposis (FAP): Autosomal dominant, APC gene mutation (chromosome 5q21); hundreds to thousands of colonic adenomatous polyps; nearly 100% risk of colorectal cancer by middle age if untreated (prophylactic colectomy recommended).
- Gardner syndrome: FAP variant with additional osteomas, epidermal cysts, and desmoid tumours.
- Turcot syndrome: FAP (or Lynch syndrome) variant with associated CNS tumours (medulloblastoma/glioblastoma).
- Peutz-Jeghers syndrome: Autosomal dominant, STK11/LKB1 mutation; multiple hamartomatous polyps throughout the GI tract with mucocutaneous melanin pigmentation (lips, oral mucosa, hands); increased risk of GI and extra-intestinal cancers (though the polyps themselves are hamartomas, not directly premalignant).
- Juvenile polyposis syndrome: Multiple juvenile (hamartomatous) polyps, autosomal dominant (SMAD4/BMPR1A mutations); increased colorectal cancer risk.
- Lynch syndrome (HNPCC): Not a polyposis syndrome per se (few polyps), but autosomal dominant mismatch repair gene mutations causing microsatellite instability and markedly increased risk of colorectal (and endometrial) cancer, typically right-sided and at a younger age.