Colorectal polyps

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Presence of polyps within the large bowel. A polyp is a macroscopic description and does not accurately indicate the nature of the lesion. It is vital to qualify the type of polyp as this dictates the clinical significance. Classification of colorectal polyps is based on histological morphology. Endoscopically, most lesions are referred to as pedunculated or sessile.

Classification. Endoscopically, pedunculated vs sessile. Histologically, the main types:

  1. Adenomatous polyps (adenomas)
  2. Flat adenomas (not strictly polyps on appearance)
  3. Hyperplastic polyps (metaplastic polyp is synonymous, but deprecated)
  4. Serrated adenomas (mixed hyperplastic-adenomatous polyps)
  5. Sessile serated adenoma

The terminology for the latter two categories is complex (see discussion below). Other rarer polyps include hamartomatous polyps, juvenile polyps, inflammatory polyps and pseudo-polyps.

There also a number of multiple polyp (polyposis) syndromes:


Adenomatous polyps

Thought to be the precursors of colorectal cancer (See Adenoma-carcinoma sequence).

Adenomas are benign neoplastic growths of glandular tissues harbouring varying degrees of dysplasia. These can adopt a tubular or villous architecture or a a combination of both. Villous adenomas are considered to be a higher risk of malignant progression, though the grade dysplasia is more important.

Hyperplastic polyps

Hyperplastic (sometimes called metaplastic) are common, but are benign and of no great significance, except when they cannot be visually distinguished from more sinister lesions. There is a thinking that they may form part of the continuum of serrated adenomas (see below)

Serrated adenomas and Sessile serrated adenomas

Polyps which showed features of hyperplastic polyps (serrated, heaped up glandular elements) and adenomatous polyps were labelled serrated adenomas. They can be considered mixed hyperplastic-adenomatous polyps. As they were described first, they are sometimes referred to as traditional serrated adenomas.

A further group of polyps were identified and felt to be distinct from the serrated adenomas. These polyps had features of traditional serrated adenomas, but maintained a sessile base. There were termed sessile serrated adenomas and significant because they are though to have microsatellite instability and represent an alternative malignant precursor to the adenoma-adenocarcinoma pathway.


Surveillance for Adenomatous polyps

Set out in BSG Guidelines.[1] Depends on:

  • Number of polyps
  • Nature of polyps
  • Patient factors:
    • age
    • comorbidity
    • family history
  • Quality of previous investigations:
    • Accuracy
    • Completeness
BSG 2002 Suggested Surveillance Following Adenoma Removal
Low Risk Intermediate Risk High Risk
1-2 adenomas
both small (<1cm)
3-4 small adenomas
at least one ≥1cm
≥5 small adenomas
≥3 at least 1 ≥1cm
5 year colonoscopy
(or no follow-up)
3 year colonoscopy 1 year colonoscopy
Findings at follow-up Findings at follow-up Findings at follow-up
No adenomas → Stop follow-up 1 negative exam → B Negative, low or intermediate risk → B
Low risk adenomas → A 2 consecutive negative exams → Stop follow-up High risk adenomas → C
Intermediate risk adenomas → B Low or intermediate risk adenomas → B
High risk adenomas → C High risk adenomas → C

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