Colon tumor
Flat adenoma of colon

Author: Charanjeet Singh, M.D. (see Authors page)

Revised: 18 September 2018, last major update May 2012

Copyright: (c) 2003-2018,, Inc.

PubMed Search: "Flat adenoma" colon

Cite this page: Singh, C. Flat adenoma of colon. website. Accessed December 13th, 2018.
Definition / general
  • 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
Gross description
  • Flat or slightly raised plaques, often with a central depression
  • Usually height 2 mm or less; may be multiple
Microscopic (histologic) description
  • 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)
Microscopic (histologic) images

Images hosted on other servers:

Flat adenoma (Figure 2)

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 / cytogenetics description