sessile serrated adenoma

Definition: Sessile serrated adenoma (SSA/P) and sessile serrated polyp (SSA/P) refer to the same serrated lesion and are currently used interchangeably. SSA/Ps are more commonly seen in the proximal colon and are usually larger than HPs.

Images

 sessile serrated adenoma

• https://twitter.com/dozing_dog/status/737896533987852288
• https://twitter.com/LizMontgomeryMD/status/1325521216833114114

 appendiceal sessile serrated adenoma (SSA/P)

• https://twitter.com/Sezin_Hatice/status/744818032027934720

SSAs are thought to represent approximately 2% of all colonoscopically removed polyps, over 8% of all polyps that were previously diagnosed as HPs and around 18% of all serrated polyps.

SSAs have been associated with proximal CRCs, high level of CIMP, BRAF mutations and MSI-high.

Microscopy

Histologic diagnosis of SSA/Ps are entirely based on architectural features characterized by:
 exaggerated crypt serration,
 serration throughout the crypt length,
 hypermucinous epithelium,
 crypt dilatation,
 crypt branching,
 horizontal crypt extensions at the crypt base,
 aberrant proliferation.

Despite the name, SSA/Ps lack the dysplastic nuclear changes that characterize conventional adenomas.

Localization

 appendiceal sessile serrated adenoma (SSA/P)

Cancer risk

Given the presumed premalignant potential, it is probably warranted for patients with SSA/ Ps to undergo endoscopic surveillance similar to those with conventional adenomas. In addition, a subset of these lesions may potentially progress to carcinoma more rapidly than conventional adenomas. Patients with these lesions may thus need an even more aggressive endoscopic surveillance.

Currently, SSAs are managed clinically in a similar fashion to colorectal adenomas (adenomatous polyps - APs).

SSAs are high-risk lesions, with 15% of the sessile serrated adenoma patients developing subsequent colorectal carcinomas or adenomatous polyps with high-grade dysplasia. This incidence is higher than that of the control HP and adenomatous polyp patients, and would support close endoscopic follow-up in patients harboring sessile serrated adenomas.

MSI

Sessile serrated adenoma (SSA) is the proposed precursor for microsatellite unstable colorectal carcinomas. SSAs should be managed similar to adenomas.

Sessile serrated adenomas (SSAs) are associated with colorectal carcinomas (CRCs) that demonstrate high microsatellite instability (MSI-H).

Synopsis

 SSA is an atypical HP variant described by Torlakovic and Snover in 1996.

• SSAs are larger (usually greater than 1 cm) than HPs.
• They are more frequently located in the right colon.
• Histologically, SSAs are distinguished from typical HPs by the presence of inverted T- or L-shaped crypt bases that reflect disordered proliferation.
• Other features include dilated crypts and serration extending into the lower third of the crypt.
• Focal nuclear stratification, mild nuclear atypia, or dystrophic goblet cells may be seen in the crypt bases.
• Moreover, SSAs show increased mucin production, absence of enteroendocrine cells, and absence of a thickened basement membrane under the surface.
• Other less common features include small foci of pseudostratification and eosinophilic change (identical to that seen in TSAs) of the surface epithelium.
• Small prominent nucleoli, open chromatin, and irregular nuclear contours also might be present, along with mitoses in the upper third of the crypts or on the surface itself.

Differential diagnosis

 colorectal hyperplastic polyps

• It should be remembered that SSA/P is a relatively new entity that used to be classified as HP in the past. Thus, pathologists may have difficulty to separate between SSA/ P and HP on histologic ground. In cases where the separation is not easy, a descriptive diagnosis of “serrated polyp” with a comment may be rendered.
• Nevertheless, the separation of SSA/P from HP appears important because SSA/P is now thought to be the precursor lesion for colorectal carcinomas with MSI and probably also for CpG island methylated MSS carcinomas, whereas HP is generally believed to be innocuous.
• The most reliable features for SSA/P to distinguish from HP are dilation of the crypts at the base, often assuming a L, inverted T, or anchor-shaped configuration.
• These unusual shapes (“architectural dysplasia”) are often observed in two or more contiguous crypts and are thought to result from abnormal proliferation and/or decreased apoptosis.

Molecular biology

Sessile serrated adenomas are characterized by a high rate of BRAF mutation, up to 95%, and are likely to be the precursor lesion of most CRCs evolving through the serrated neoplasia pathway.

Open references

 Sessile serrated adenoma/polyps: Where are we at in 2016?
Singh R, Zorrón Cheng Tao Pu L, Koay D, Burt A.
World J Gastroenterol. 2016 Sep 14;22(34):7754-9. doi : 10.3748/wjg.v22.i34.7754
PMID: 27678358 Free

 Screening, management and surveillance for the sessile serrated adenomas/polyps. Fu X, Qiu Y, Zhang Y. Int J Clin Exp Pathol. 2014 Mar 15;7(4):1275-85. PMID: 24817924 [Free]

 http://www.thejgo.org/article/view/410/821

 Serrated polyposis syndrome: Molecular, pathological and clinical aspects. Carla Guarinos et al., 2012. World J Gastroenterol 2012 May 28; 18(20): 2452-2461 - http://www.wjgnet.com/1007-9327/full/v18/i20/2452.htm

References

 Molecular features of colorectal hyperplastic polyps and sessile serrated adenoma/polyps from Korea. Kim KM, Lee EJ, Ha S, Kang SY, Jang KT, Park CK, Kim JY, Kim YH, Chang DK, Odze RD. Am J Surg Pathol. 2011 Sep;35(9):1274-86. PMID: 21836485

 Histologic and Molecular Analyses of Colonic Perineurial-like Proliferations in Serrated Polyps: Perineurial-like Stromal Proliferations Are Seen in Sessile Serrated Adenomas. Pai RK, Mojtahed A, Rouse RV, Soetikno RM, Kaltenbach T, Ma L, Arber DA, Plesec TP, Goldblum JR, Pai RK. Am J Surg Pathol. 2011 Sep;35(9):1373-80. PMID: 21836484

 Sessile serrated adenoma with early neoplastic progression: a clinicopathologic and molecular study. Fujita K, Yamamoto H, Matsumoto T, Hirahashi M, Gushima M, Kishimoto J, Nishiyama K, Taguchi T, Yao T, Oda Y. Am J Surg Pathol. 2011 Feb;35(2):295-304. PMID: 21263251

 Longitudinal outcome study of sessile serrated adenomas of the colorectum: an increased risk for subsequent right-sided colorectal carcinoma. Lu FI, van Niekerk de W, Owen D, Tha SP, Turbin DA, Webber DL. Am J Surg Pathol. 2010 Jul;34(7):927-34. PMID: 20551824

 Beta-catenin Nuclear Labeling is a Common Feature of Sessile Serrated Adenomas and Correlates With Early Neoplastic Progression After BRAF Activation. Yachida S, Mudali S, Martin SA, Montgomery EA, Iacobuzio-Donahue CA. Am J Surg Pathol. 2009 Sep 9. PMID: 19745699

 Torlakovic EE, Gomez JD, Driman DK, Parfitt JR, Wang C, Benerjee T, Snover DC. Sessile serrated adenoma (SSA) vs. traditional serrated adenoma (TSA). Am J Surg Pathol. 2008 Jan;32(1):21-9. PMID: 18162766

 Farris AB, Misdraji J, Srivastava A, Muzikansky A, Deshpande V, Lauwers GY, Mino-Kenudson M. Sessile serrated adenoma: challenging discrimination from other serrated colonic polyps. Am J Surg Pathol. 2008 Jan;32(1):30-5. PMID: 18162767