Sessile Serrated Polyp/Adenoma of the Appendix

Definition

• Cytologically bland appendiceal lesion composed of serrated glands with architectural disturbances of the deep crypts

Diagnostic Criteria

• Mucosal hyperplasia, hyperplastic polyp and sessile serrated polyp/adenoma have quite similar appearances in the appendix
• They are distinguished architecturally as all lack cytologic dysplasia
• Architectural distortion due to obstructive changes may make the distinctions difficult
• Criteria for their distinction have not been tested for reproducibility in the appendix
• Criteria for the individual lesions are based on those used in the colorectum
• Appearance is similar to sessile serrated polyp/adenoma of the colorectum
  • Serration is variably present throughout gland length
    • Usually exaggerated serration
    • Apical cytoplasm typically filled with microvesicular mucin
      • Goblet cells not conspicuous
  • Base of crypts show architectural disturbances
    • Dilation of crypts
    • Branching
    • Horizontal glands at base
      • “L shaped” or “hockey stick”
    • Mature mucinous cells at base of crypts
      • May form serrations at base
    • Who requires 3 such abnormal crypts to make the diagnosis while a recent consensus conference proposes that one is enough (Rex 2012)
  • Aberrant proliferation
    • Proliferative zone frequently displaced from base
      • Irregularly elevated at least into mid crypt
• Significant nuclear dysplasia is not a feature of pure sessile serrated polyp/adenoma
• Nuclear stratification and loss of polarity are not seen
• Nuclei may be mildly atypical with open chromatin and distinct nucleoli
• Presence of dysplasia in a lesion with hyperplastic features suggests either
• Traditional serrated adenoma if present throughout
• Sessile serrated adenoma with dysplasia if focal
• Clinical significance of appendiceal SSA is currently unknown
• No relationship to pseudomyxoma peritonei has been demonstrated
• One study (Renshaw 2006) found SSP in 20% of appendicitis cases over 30 years of age
• None found <30
• Most identified only if appendix entirely embedded
• Unclear significance
• Carcinomas have been reported associated with appendiceal SSA
  • Frequency is unknown

Original posting/updates : 10/7/10, 3/20/13

Supplemental studies

No studies currently useful for diagnosis, but following may shed some light on the nature of serrated lesions of the appendix (based on Yantiss 2007)

• CpG island DNA hypermethylation is evident in about half of appendiceal hyperplastic polyps, sessile serrated adenomas, traditional serrated adenomas, and SSA with dysplastic foci (SSAD)
• MLH1 staining is lost in about 50% of all four
  • Nevertheless, MSI is extremely rare in all four
• MGMT staining is lost in about 50% of HP, SSA and TSA, and 100% of SSAD
• BRAF is mutated in 20-25% of HP, TSA and SSAD and 47% of SSA
• KRAS is mutated in 20-40% of all four
• Only 1 of 4 carcinomas associated with SSA was MSI high
• No clear pattern of progression to support a serrated neoplasia pathway as in the colorectum

Differential Diagnosis

Appendiceal hyperplastic polyp should be distinguished from appendiceal sessile serrated adenoma using the same features as in the colorectum

Appendiceal Hyperplastic Polyp / Mucosal Hyperplasia	Appendiceal Sessile Serrated Polyp/Adenoma
Bases of crypts straight, regular, frequently pointed	Crypts dilated, branched, occasional horizontal bases
Serrations restricted to upper part of glands	Serrations may involve base
Proliferative zone reliably restricted to base	Proliferative zone frequently irregularly displaced upwards from the base

The distinction may be particularly difficult in the appendix
Both are benign if completely excised and completely sectioned

Lists

Appendiceal Epithelial Neoplasms and Proliferations

• Adenocarcinoma
• Carcinoid / well differentiated neuroendocrine neoplasm
• Carcinoma ex-goblet cell carcinoid
• Goblet cell carcinoid
• Hyperplastic polyp / mucosal hyperplasia
• Mucinous adenoma / cystadenoma
• Mucinous neoplasm with high risk of recurrence
• Mucinous neoplasm with low risk of recurrrence
• Sessile serrated polyp / adenoma
• Traditional serrated adenoma

Clinical / Descriptive Terms

• Mucocele
• Pseudomyxoma peritonei

Bibliography

• Yantiss RK, Panczykowski A, Misdraji J, Hahn HP, Odze RD, Rennert H, Chen YT. A comprehensive study of nondysplastic and dysplastic serrated polyps of the vermiform appendix. Am J Surg Pathol. 2007 Nov;31(11):1742-53.
• Renshaw AA, Kish R, Gould EW. Sessile serrated adenoma is associated with acute appendicitis in patients 30 years or older. Am J Clin Pathol. 2006 Dec;126(6):875-7.
• Rex DK, Ahnen DJ, Baron JA, Batts KP, Burke CA, Burt RW, Goldblum JR, Guillem JG, Kahi CJ, Kalady MF, O'Brien MJ, Odze RD, Ogino S, Parry S, Snover DC, Torlakovic EE, Wise PE, Young J, Church J. Serrated lesions of the colorectum: review and recommendations from an expert panel. Am J Gastroenterol. 2012 Sep;107(9):1315-29