Colon tumor - Flat adenoma of colon

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Colon tumor

Polyps

Flat adenoma of colon

Reviewers: Charanjeet Singh, M.D. (see Reviewers page)
Revised: 16 May 2012, last major update May 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Also called depressed adenoma
● Present in asymptomatic populations (Gut 1998;43:229)
● More difficult to detect during endoscopy, but targeted indigo carmine chromoscopy or other methods are useful
● Diagnosis requires (a) classic endoscopic (gross) appearance of mucosal elevation with flat / rounded surface and height less than half the diameter, (b) not resembling a hyperplastic polyp and (c) dysplastic changes
● Another study defined flat as thickness of 1.3 mm or less or thickness less than twice normal mucosal thickness
● Controversial if associated with higher risk for high grade dysplasia (no-Clin Gastroenterol Hepatol 2004;2:905, yes-Dis Colon Rectum 1991;34:981)
● Risk may be higher if central depression, individual history or family history of malignancy (Dis Colon Rectum 2000;43:782), or larger lesion (Dis Colon Rectum 1985;28:847)

Case reports
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● 74 year old man with deep malignant component (Virchows Arch A Pathol Anat Histopathol 1993;422:415)

Gross description
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● Flat or slightly raised plaques, often with a central depression
● Usually height 2 mm or less; may be multiple

Micro description
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● Plaque-like, not polypoid or exophytic
● Up to twice the thickness of adjacent normal epithelium
● Usually tubular adenomas that show superficial adenomatous changes at periphery, and centrally may extend throughout the crypt
● Also associated with aberrant crypt foci (Am J Gastroenterol 2005;100:1283)

Micro images
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Flat adenoma

MUC2-left; MUC1-right

A: flat adenoma; B: MUC2+; C: MUC1+ only focally

A: flat adenoma; B: MUC2+; C: MUC1+ at base of crypts

Molecular description
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● Some cases have multiple APC mutations (Eur J Hum Genet 1999;7:928)

Additional references
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● Hum Pathol 1991;22:70, Am J Gastroenterol 2006;101:172

End of Colon tumor > Polyps > Flat adenoma of colon

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