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Surgical Pathology Criteria
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Appendiceal Mucinous Neoplasm with Low Risk of Recurrence

Definition

  • Appendiceal neoplasm with features of mucinous adenoma but with extra-appendiceal acellular mucin

Alternate/Historical Names

  • Borderline mucinous tumor
  • Disseminated peritoneal adenomucinosis
  • Low grade mucinous neoplasm (WHO preferred term, includes low and high risk of recurrence neoplasms, see Controversy)
  • Mucinous neoplasm of low malignant potential

Diagnostic Criteria

  • Features of mucinous adenoma (see detailed adenoma criteria)
    • Simple mucinous columnar epithelium
    • Low grade dysplasia
    • Sessile, usually circumferential, lining of appendiceal luminal surface
  • Frequent mucin dissection of the wall
    • May contain neoplastic epithelium within intramural mucin only
    • No clear direct invasion of the wall by neoplastic epithelium
  • EXCEPT either of the following is present
    • Extra-appendiceal acellular mucin, or
    • Mucinous adenoma with transection of neoplasm at the margin of resection
  • Specimen should be entirely submitted before this diagnosis is made
  • A very low percentage will recur
    • Reported rates 4-8% but none of the recurrrent cases were entirely embedded for sections
    • No deaths reported
Teri A Longacre MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting/updates : 10/7/10, 2/10/12, 3/6/12

Controversy

  • Low grade mucinous neoplasm - WHO proposed alternate name
    • Term proposed to encompass mucinous neoplasms with low and high risks of recurrence
    • Proposed because all are composed of histologically identical adenomatous appearing epithelium
    • We prefer not to combine these processes as their clinical behavior is quite different
      • Mucinous neoplasm with low risk of recurrence has very low morbidity and mortality
      • Mucinous neoplasm with high risk of recurrence has considerable morbidity and mortality
    • Furthermore, the term could be confused with low grade adenocarcinoma
      • This is an ordinary colonic type adenocarcinoma, which has a more aggressive course

Differential Diagnosis

Appendiceal Mucinous Neoplasms
Mucinous Adenoma/Cystadenoma Mucinous Low Risk of Recurrence Mucinous High Risk of Recurrence Mucinous Adenocarcinoma
No extra-appendiceal mucin No epithelium in extra-appendix mucin Epithelium present in extra-appendiceal mucin Epithelium may be present in extra-appendiceal mucin
Non-invasive epithelium may be present in intramural mucin Non-invasive epithelium may be present in intramural mucin Non-invasive epithelium may be present in intra and extramural mucin Invasion by jagged neoplastic glands
Margin of resection must be clear Margin may be involved Margin may be involved Margin may be involved
Benign, no recurrences Very few recur, 0% mortality Frequently recur, 50% 5 year, 20% 10 year survival <10% 10 yr survival

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