Sessile serrated adenoma

Editorial Board Member: Monika Vyas, M.D.
Deputy Editor-in-Chief: Catherine E. Hagen, M.D.
Enoch Kuo, M.D.
Raul S. Gonzalez, M.D.

Last author update: 28 October 2021
Last staff update: 5 May 2022

Copyright: 2003-2023,, Inc.

PubMed search: Sessile serrated adenoma [title]

Enoch Kuo, M.D.
Raul S. Gonzalez, M.D.
Page views in 2022: 35,634
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Cite this page: Kuo E, Gonzalez RS. Sessile serrated adenoma. website. Accessed November 29th, 2023.
Definition / general
  • Serrated neoplastic precursor lesion of colorectal cancer (Am J Gastroenterol 2012;107:1315)
  • Defined as having 2 or 3 contiguous crypts demonstrating features of sessile serrated adenoma, as discussed below (per Bosman: WHO Classification of Tumours of the Digestive System, 4th Edition, 2010)
  • Criteria for serrated polyposis syndrome include 1 of the following:
    • At least 5 serrated polyps proximal to the sigmoid colon with at least 2 greater than 1 cm in size
    • Any serrated polyp proximal to the sigmoid colon in a patient with a first degree relative with serrated polyposis syndrome
    • More than 20 serrated polyps of any size in the colon
Essential features
  • Neoplastic, premalignant lesion of the colorectum
  • If present, patient should undergo increased colonoscopy surveillance
  • May develop traditional cytologic dysplasia and progress to colorectal carcinoma with microsatellite instability
  • Current official WHO designation is sessile serrated lesion; former WHO designation was sessile serrated adenoma / polyp
  • Examples that develop adenomatous epithelium are termed sessile serrated adenoma with cytologic dysplasia (Gastrointest Endosc 2014;80:307)
ICD coding
  • ICD-10: K63.5 - Colon polyp
Clinical features
  • Incidental findings on colonoscopy and have no clinical features unless they progress to malignancy
Radiology description
Prognostic factors
Gross description
Gross images

Images hosted on other servers:

Sessile serrated adenoma on colonoscopy

Sessile serrated
adenoma before
and after endoscopic

Microscopic (histologic) description
  • Sawtooth serrations of the epithelium with abundant mucin, similar to hyperplastic polyps
  • Basal crypt dilation with mucous retention
  • Bases of the crypts are more serrated compared to the surface and have mature goblet cells and mucinous cells (Am J Gastroenterol 2012;107:1315)
  • Lateral spread of the crypt bases (commonly described as boot shaped or anchor shaped crypts)
  • May contain fibroblastic / perineuriomatous stroma (Am J Surg Pathol 2011;35:1373)
  • Conventional ("adenomatous") dysplasia may also be present, with retention of MLH1 staining; no need to grade per WHO
  • Nonconventional forms of dysplasia have also been described, including minimal deviation type (mild architectural and histologic changes, difficult to see on H&E but shows loss of MLH1), serrated type (tightly packed glands with rounded dysplastic nuclei and eosinophilic cytoplasm; MLH1 retained) and not otherwise specified (most common pattern; atypical changes not fitting into any other pattern; often MLH1 loss) (Mod Pathol 2017;30:1728, Mod Pathol 2019;32:1390)
Microscopic (histologic) images

Contributed by Monika Vyas, M.D. and Christopher Hartley, M.D.

SSA with dysplasia

MLH1 loss

Sessile serrated adenoma with adenomatous dysplasia

Contributed by Raul S. Gonzalez, M.D.

Sessile serrated adenoma / polyp

Contributed by @RaulSGonzalezMD on Twitter
Sessile serrated adenoma Sessile serrated adenoma

Sessile serrated adenoma

Images hosted on other servers:

Sessile serrated adenoma / polyp

Ascending colon

Sessile serrated adenoma


Positive stains
Negative stains
Molecular / cytogenetics description
Sample pathology report
  • Ascending colon, polyp, endoscopic mucosal resection:
    • Sessile serrated lesion
    • Lateral margins of resection unremarkable.
Differential diagnosis
Additional references
Board review style question #1
What mutations can be seen in sessile serrated adenoma?

  1. Beta catenin and KRAS
  2. BRAF and beta catenin
  3. BRAF and CpG island methylator phenotype (CIMP)
  4. KRAS and CpG island methylator phenotype (CIMP)
Board review style answer #1
C. BRAF and CpG island methylator phenotype (CIMP). KRAS and beta catenin mutations are not associated with sessile serrated adenomas and are instead seen in traditional serrated adenomas and tubular adenomas.

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Reference: Sessile serrated adenoma
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