Sessile Serrated Polyp/Adenoma of the Appendix

Definition

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

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

No relationship to pseudomyxoma peritonei has been demonstrated
One study (Renshaw 2006) found SSP in 20% of appendicitis cases over 30 years of age

Carcinomas have been reported associated with appendiceal SSA
- Frequency is unknown

Teri A Longacre MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342