Mucinous Adenoma / Cystadenoma of the Appendix

Definition

• Circumferential lining of appendiceal luminal surface by low grade dysplastic epithelium

Diagnostic Criteria

• Simple adenomatous mucinous columnar epithelium
• Focal nuclear stratification may be present
• Contains occasional goblet cells
• May be cuboidal or flat from compression
• Low grade dysplasia
• Mitotic figures, if present, are not atypical
• Must not exhibit high grade dysplasia
• No high grade cytologic features or cribriform architecture
• No invasion
• No direct invasion of muscular wall by jagged neoplastic glands
• Muscularis mucosae may be attenuated by distension making evaluation difficult
• Intramural mucin containing epithelium may be present
• No extra-appendiceal mucin with or without epithelium
• Proximal margin of appendix must not be involved
  • If involved, designate as low risk of recurrence
• Sessile, usually circumferential, lining of appendiceal luminal surface
  • May be undulating or villous
• Commonly associated with luminal dilation
• Common cause of mucocele
• Wall of appendix may calcify
• Specimen should be entirely submitted before this diagnosis is made
• Myxoglobulosis may be seen occasionally
  • Pearl-like globules of acellular laminated mucin surrounding an amorphous granular and mucinous core
• 1-10 mm
• May calcify peripherally
• Present in lumen or periappendiceal tissue
• May be associated with colorectal adenoma or carcinoma and ovarian mucinous tumor
• Justifies consideration for screening
• Benign, does not recur after resection
• Only if all criteria are met
• If any finding is equivocal, it is best to designate as a mucinous neoplasm with low risk of recurrrence
• Not a cause of pseudomyxoma peritonei if strictly defined as above
• Usual colonic type adenomas are extremely rare

Original posting/updates : 10/7/10

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

Distinction from traditional serrated adenoma may be difficult in lesions compressed by mucin distension

• TSA can generally be recognized by its complex glandular architecture and prominent glandular serration
• Mucinous adenoma is flat with areas of short villi and lacks serrated appearance
• If completely excised and completely sectioned, both are benign

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.
• Gonzalez JE, Hann SE, Trujillo YP. Myxoglobulosis of the appendix. Am J Surg Pathol. 1988 Dec;12(12):962-6.
• Viswanath YK, Griffiths CD, Shipsey D, Oriolowo A, Johnson SJ. Myxoglobulosis, a rare variant of appendiceal mucocele, occurring secondary to an occlusive membrane. J R Coll Surg Edinb. 1998 Jun;43(3):204-6