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Hyperplastic Polyp / Mucosal Hyperplasia of the Appendix

Definition

  • Serrated mucosal proliferations in the appendix lacking both architectural and cytological dysplasia

Diagnostic Criteria

  • Mucosal hyperplasia, hyperplastic polyp and sessile serrated polyp have quite similar appearances in the appendix
    • Architectural distortion due to obstructive changes may make the distinctions difficult
    • Criteria for their distinction have not been tested for reproducibility in the appendix
    • Architectural criteria for separation of sessile serrated polyp from hyperplastic lesions are based on those used in the colorectum
  • Appearance is similar to hyperplastic polyp of the colorectum
    • Upper (luminal) portion of polyp has a “saw tooth” appearance
    • Nuclei are small, regular, round and basal
      • Best evaluated on or near the luminal surface
    • Bases of crypts show proliferative changes
  • It is not clear that hyperplastic polyps and mucosal hyperplasia can or need to be separated in the appendix
    • Polypoid vs. sessile distinction has been proposed
      • This is not reliably made in the appendix
      • Both are common incidental lesions
      • Both are uncommonly associated with appendiceal dilation
      • Neither has been shown to be a precursor of carcinoma or be associated with pseudomyxoma peritonei
  • The entire appendix should be examined microscopically

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

Original posting/updates : 10/21/10

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

Clinical / Descriptive Terms

Bibliography

  • Pai RK, Longacre TA. Appendiceal mucinous tumors and pseudomyxoma peritonei: histologic features, diagnostic problems, and proposed classification. Adv Anat Pathol. 2005 Nov;12(6):291-311.
  • 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.
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