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

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

The distinctions are critical

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

• 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.
• Pai RK, Beck AH, Norton JA, Longacre TA. Appendiceal mucinous neoplasms: clinicopathologic study of 116 cases with analysis of factors predicting recurrence. Am J Surg Pathol. 2009 Oct;33(10):1425-39.
• Molavi D, Argani P. Distinguishing benign dissecting mucin (stromal mucin pools) from invasive mucinous carcinoma. Adv Anat Pathol. 2008 Jan;15(1):1-17.
• Bosman FT, Carneiro F, Hruban RH, Thiese ND (Eds). WHO Classifiication of Tumors of the Digestive System, IARC, Lyon 2010
• Yantiss RK, Shia J, Klimstra DS, Hahn HP, Odze RD, Misdraji J. Prognostic significance of localized extra-appendiceal mucin deposition in appendiceal mucinous neoplasms. Am J Surg Pathol. 2009 Feb;33(2):248-55
• Arnason T, Kamionek M, Yang M, Yantiss RK, Misdraji J. Significance of proximal margin involvement in low-grade appendiceal mucinous neoplasms. Arch Pathol Lab Med. 2015 Apr;139(4):518-21. doi: 10.5858/arpa.2014-0246-OA. Epub 2014 Jun 27. PubMed PMID: 24971927.