Colorectal polyps

Abnormal protrusion of mucosa into bowel lumen, resulting from overgrowth of epithelial lining

Classification by endoscopic appearance

• Pedunculated
• Sessile

Classification by histological appearance

Non-neoplastic polyps

• • Inflammatory polyps (pseudopolyps)
    • Found in regions of healing inflammation - contains inflammatory cells along with epithelial/stromal components
    • Irregularly shaped islands of intact mucosa neighbouring areas of mucosal ulceration/regeneration
    • Typically seen in association with IBD
    • Can be associated with surrounding dysplasia in patients with IBD
    • No intrinsic neoplastic potential, but can be large, mimicking a neoplasm
  • Hamartomatous polyps
    • Tissue normally found at that site, but growing in a disorganised mass
    • Juvenile polyps
      • Hamartomatous lesions that consist of a lamina propria and dilated cystic glands, rather than increased numbers of epithelial cells
      • Can be diagnosed at any age, although more common in childhood
      • Not associated with increased CRC risk unless in the setting of juvenile polyposis syndrome
    • Peutz-Jeghers polyps
      • Hamartomatous lesion of glandular epithelium supported by smooth muscle cells that is contiguous with the muscularis mucosa
      • Usually, but not always, associated with PJS
    • Cronkhite-Canada syndrome
    • Can cause obstruction or bleeding, otherwise don't necessarily need to be removed
• Sessile serrated lesions
  • Hyperplastic polyps
    • Most common benign polyps - no malignant potential
    • Typically <5mm, in rectosigmoid
    • Typically sessile, smooth surface, slight pink discolouration
    • Consist of elongated colonic crypts with a papillary configuration of epithelial cells without atypia
    • Lots of hyperplastic polyps in the rectum is not associated with cancer elsewhere, and does not shorten the recommended screening interval
  • Sessile serrated adenomas
    • Previously classified as hyperplastic
    • More prevalent in right colon and more common in women
    • 'Traditional serrated adenomas' are a separate subtype and are often found in rectosigmoid
    • Endoscopic: smooth, 'cloud-like' surface, often flat or sessile, and can have mucus covering.
    • Histopathology: combinations of adenomatous and hyperplastic polyps, sharing features of both types including colonic crypts with a saw-toothed serrated configuration and nuclear atypia.
      • 37% have 'significant' dysplasia
      • 11% have CIS
      • Thought to be the precursor lesion to sporadic MSI-H colon cancers (CpG island hypermethylation phenotype)
      • Activation of BRAF oncogene is a features of many SSAs
    • Disproportionately high risk for progression to cancer - possibly faster progression, easier to miss, incomplete removal

Neoplastic polyps (adenoma)

• • As opposed to benign - these polyps have cellular atypia and all have malignant potential
  • Most common neoplastic type (two thirds of all polyps)
  • 30-50% have multiple - if you find one, keep looking
  • Overall prevalence 25% at 50 years old, 50% by 70 years
  • Grow at 0.5mm/year
  • 5% progress to cancer over 10 years
    • High-risk if >1cm, sessile, high-grade dysplasia, or villous component
  • Tubular adenomas - 70-80% of polyps removed - branched tubular glands
  • Villous adenomas - long finger-like projections of surface epithelium (serpentine appearance)
  • Tubulovillous - elements of both types

Malignant polyps

• • Histologic examination reveals a focus of carcinoma that has invaded through the muscularis mucosa
  • Depth of penetration is crucial - Haggitt classification
    • Level 0: Carcinoma is limited to the mucosa - carcinoma-in-situ
    • Level 1: Carcinoma invading into the submucosa, limited to the head of the polyp
    • Level 2: Carcinoma invading to the level of the neck (junction of the head and the stalk)
    • Level 3: Carcinoma invading any part of the stalk
    • Level 4: Carcinoma invading into the submucosa of the colon wall, below the level of the stalk, but above the muscularis propria. 12-25% lymph node metastases - usually suggest resection.
    • Sessile polyps with invasion of the muscularis mucosa are by definition Haggitt level 4.
  • Kikuchi classification: depth of submucosal invasion correlates with increased risk of lymph node metastasis
    • Sm1: invasion into the upper third of the mucosa
    • Sm2: Invasion into the middle third of the mucosa. 8-10% lymph node metastasis risk.
    • Sm3: Invasion into the lower third of the mucosa 25% metastasis risk.
  • Indications for completion segmental colectomy for malignant polyps: (in these cases, the risk of residual cancer and lymph node metastasis is >10%)
    • Pedunculated Haggitt level 4
    • Sessile Kikuchi level Sm2 or Sm3
    • Histological poor differentiation
    • Lymphovascular invasion
    • Incomplete removal or close resection margins
    • Other high-risk polyps based on risk calculators

Presentation

• Usually asymptomatic
• Complications:
  • Bleeding
  • Obstruction
  • Malignant transformation

Post-polypectomy surveillance

• See separate topic under 'Endoscopy'

Metastases risk

• Pedunculated
  • Dutch T1 pedunculated polyp calculator https://t1crc.com/calculator/pedunculated/
    • Differentiation
    • Haggitt level
    • Budding
    • Poorly-differentiated clusters
    • LVI
    • Status of muscularis mucosae
  • Malignantpolyp.com