Sessile serrated adenoma

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Sessile serrated adenoma, abbreviated SSA, is a premalignant polyp of the large bowel. It is also known as sessile serrated polyp (abbreviated SSP), sessile serrated lesion and sessile serrated adenoma/polyp (abbreviated SSA/P).

Sessile serrated adenoma
Diagnosis in short

SSA. H&E stain.

LM serrated epithelium, crypt base dilation, crypt branching, boot-shaped glands, horizontal glands
LM DDx hyperplastic polyp, tubular adenoma (when with dysplasia)
Site colon - usually cecum or ascending colon

Associated Dx colorectal adenocarcinoma, hyperplastic polyp
Syndromes serrated polyposis syndrome

Prevalence common
Endoscopy flat, usually > 5 mm, mucinous cap
Clin. DDx normal, hyperplastic polyp

General

Epidemiology:

  • Thought to lead to colorectal cancer through a different pathway that most tumours in the left colon/rectum.
  • Microvesicular hyperplastic polyps are hypothesized to be the the precursor of SSAs.[1]

Gross

Features:[2]

  • Flat lesions, usually > 5 mm.
  • Typically have a "mucous cap" - present ~65% of the time; useful for identification.
  • Border not well-demarcated.
  • More common in the proximal colon.

Note:

  • Sessile lesions over 1 cm are usually SSAs.[2]

Image:

Microscopic

Features:

  • Serrated epithelium at the surface and deep in the crypts.
    • Saw-tooth appearance, epithelium has jagged appearing edge.
  • Crypt dilation at base with serrations - key feature.
    • Very common -- anecdotally the most sensitive feature.
  • "Boot"-shape or "L"-shaped glands.
    • Shape may be similar to a hockey stick.
  • Horizontal crypts = crypt long axis parallel to the muscularis mucosae.
  • Crypt branching.

Minimal extent criteria - number of abnormal crypts with the above features:

  • German Society of Pathology proposal: at least two abnormal crypts -- crypts do not have to be adjacent.[4][5]
  • An expert panel lead by Rex states that one unequivocally altered crypt should prompt calling SSA.[2]
  • The WHO requires - depending on what you read:
    • Three adjacent crypts to be abnormal.[6]
    • Two or three adjacent crypts to be abnormal.[4]

Notes:

  • Typically do not have nuclear atypia, i.e. no nuclear crowding, no nuclear hyperchromasia, no cigar-shaped nuclei.
    • SSAs with nuclear atypia may be referred to as advanced sessile serrated adenomas.

DDx

Images

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COLONIC POLYP, ASCENDING COLON, BIOPSY: 
- SESSILE SERRATED ADENOMA.
- NEGATIVE FOR DYSPLASIA.
COLONIC POLYP, ASCENDING COLON, BIOPSY: 
- SESSILE SERRATED ADENOMA WITH DYSPLASIA.

Note:

  • The above exactly mirrors the Canadian consensus.[7]

References

  1. Huang, CS.; Farraye, FA.; Yang, S.; O'Brien, MJ. (Feb 2011). "The clinical significance of serrated polyps.". Am J Gastroenterol 106 (2): 229-40; quiz 241. doi:10.1038/ajg.2010.429. PMID 21045813.
  2. 2.0 2.1 2.2 Rex, DK.; Ahnen, DJ.; Baron, JA.; Batts, KP.; Burke, CA.; Burt, RW.; Goldblum, JR.; Guillem, JG. et al. (Sep 2012). "Serrated lesions of the colorectum: review and recommendations from an expert panel.". Am J Gastroenterol 107 (9): 1315-29; quiz 1314, 1330. doi:10.1038/ajg.2012.161. PMID 22710576.
  3. Rex DK, Hewett DG, Snover DC (December 2010). "Editorial: Detection targets for colonoscopy: from variable detection to validation". Am. J. Gastroenterol. 105 (12): 2665–9. doi:10.1038/ajg.2010.330. PMID 21131934.
  4. 4.0 4.1 Ensari, A.; Bilezikçi, B.; Carneiro, F.; Doğusoy, GB.; Driessen, A.; Dursun, A.; Flejou, JF.; Geboes, K. et al. (Nov 2012). "Serrated polyps of the colon: how reproducible is their classification?". Virchows Arch 461 (5): 495-504. doi:10.1007/s00428-012-1319-7. PMID 23052370.
  5. Aust, DE.; Baretton, GB. (Sep 2010). "Serrated polyps of the colon and rectum (hyperplastic polyps, sessile serrated adenomas, traditional serrated adenomas, and mixed polyps)-proposal for diagnostic criteria.". Virchows Arch 457 (3): 291-7. doi:10.1007/s00428-010-0945-1. PMID 20617338.
  6. URL: http://surgpathcriteria.stanford.edu/gitumors/sessile-serrated-polyp-adenoma/. Accessed on: 26 September 2012.
  7. Driman, DK.; Marcus, VA.; Hilsden, RJ; Owen, DA (2012). "Pathologic reporting of colorectal polyps: pan-Canadian consensus guidelines". Canadian Journal of Pathology 4 (3): 81-90.