Subtitle: Serrated colorectal polyps (WHO 2019): hyperplastic polyp, sessile serrated lesion and traditional serrated adenoma, diagnostic criteria, site and endoscopy, the serrated pathway (BRAF, CIMP, MLH1), serrated polyposis syndrome, three virtual slides and 8 MCQs.
Author: PathologyMCQ Editorial Board
Category: Gastrointestinal Pathology
Last Updated: October 2026
Read Time: 7 minutes
At-a-Glance
- Three types: hyperplastic polyp (HP), sessile serrated lesion (SSL) and traditional serrated adenoma (TSA).
- SSL: one unequivocal distorted serrated crypt is enough (WHO 2019); usually right-sided.
- TSA: villiform, ectopic crypt foci, eosinophilic cells with pencillate nuclei; usually left-sided.
- SSLs and TSAs are precursors of colorectal cancer via the serrated pathway.
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Types and Sites
Serrated polyps are named for the saw-toothed outline of their crypts. HPs are the commonest and are usually small and distal. SSLs favour the proximal colon (caecum and ascending colon). TSAs occur anywhere but are commoner in the distal colon and rectum. HPs are not considered precursors, whereas SSLs and TSAs can progress to carcinoma.
Clinical and Endoscopic Findings
Most serrated polyps are asymptomatic and found at screening colonoscopy; larger lesions may bleed. SSLs are subtle: flat or sessile, pale, with indistinct borders and a mucus cap, so they are easily missed. TSAs are usually protuberant or pedunculated with a lobulated, pine-cone-like surface.
Histology Compared
| Feature | Hyperplastic polyp | Sessile serrated lesion | Traditional serrated adenoma |
|---|---|---|---|
| Architecture | Straight, evenly spaced crypts; serration in upper half | Distorted crypts: basal dilatation, L- or inverted-T (boot) shapes, horizontal growth | Villiform or filiform; ectopic crypt foci; slit-like serrations |
| Proliferative zone | Crypt base | Displaced, asymmetric | Ectopic crypts |
| Cytology | Bland; goblet-cell rich or microvesicular | Bland (no dysplasia in most) | Tall eosinophilic cells with pencillate nuclei |
| Dysplasia | Absent | In a subset (SSL with dysplasia) | May develop conventional or serrated dysplasia |
| Usual site | Distal colon, rectum | Proximal colon | Distal colon, rectum |
| Molecular | BRAF (MVHP) or KRAS (GCHP) | BRAF V600E, CIMP | KRAS or BRAF |
Diagnostic Criteria (WHO 2019)
Hyperplastic polyp: serrations limited to the surface epithelium and superficial crypts, proliferative zones limited to the crypt bases and evenly spaced crypts. Basal dilatation, significant distortion and submucosal misplacement are absent.
Sessile serrated lesion: at least one unequivocal architecturally distorted serrated crypt is required.
Traditional serrated adenoma: villous (filiform) or tubulovillous architecture, often with bulbous tips, ectopic crypt foci, and cells with eosinophilic cytoplasm and basal or central elongated (pencillate) nuclei.
Virtual Slides
Compare the three serrated polyps side by side.
What to look for
Drag to pan · pinch or double-tap to zoom · use the + / − buttons
Read more: Hyperplastic polyp pathology → · Hamartomatous polyp syndromes →
The Serrated Pathway
SSLs carry BRAF V600E mutations and develop CpG island methylation (CIMP-high); methylation of MLH1 leads to SSL with dysplasia and sporadic MSI-high carcinoma. TSAs more often carry KRAS mutations and progress through a microsatellite-stable route. This explains why sporadic MSI-H cancers are typically right-sided and BRAF-mutant.
Serrated Polyposis Syndrome
WHO 2019 criteria (either is sufficient):
- At least 5 serrated lesions or polyps proximal to the rectum, all ≥5 mm, with at least 2 ≥10 mm.
- More than 20 serrated lesions or polyps of any size throughout the large bowel, with at least 5 proximal to the rectum.
Case Question
A right-sided, flat colonic polyp shows serrations extending to the base of the crypts, dilated inverted-T and boot-shaped crypts, and crypt branching. What is the diagnosis? A. Sessile serrated lesion · B. Hyperplastic polyp · C. Traditional serrated adenoma
Show answer
A. Sessile serrated lesion. Clues: serrations extending to the crypt base, dilated inverted-T or boot-shaped crypts, and crypt branching.
Test Yourself: 8 MCQs
Serrated polyps: 8 MCQs
HP, SSL, TSA, molecular pathways and SPS criteria, with instant explanations.
More practice: the question banks →
Exam Pearls
- One distorted crypt = SSL (WHO 2019).
- Pencillate nuclei and ectopic crypt foci = TSA.
- SSL → BRAF, CIMP, MLH1 methylation → MSI-H cancer.
- SSL with dysplasia: report it; it progresses quickly.
For tips, pitfalls, notes, reporting templates and worksheets, join the approach-based course in histopathology and cytology →
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Related reads: Hyperplastic polyp pathology → · Hamartomatous polyp syndromes →
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References
- WHO Classification of Tumours Editorial Board. Digestive System Tumours. 5th ed. IARC; 2019.
- Bateman AC, Shepherd NA. UK guidance for the pathological reporting of serrated lesions of the colorectum. J Clin Pathol. 2015;68:585–91.
- Mezzapesa M, et al. Serrated colorectal lesions: an up-to-date review from histological pattern to molecular pathogenesis. Int J Mol Sci. 2022;23:4461.
- Jaravaza DR, Rigby JM. Hyperplastic polyp or sessile serrated lesion? The contribution of serial sections to reclassification. Diagn Pathol. 2020;15:140.
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