title: Comparison of the clinicopathologic features between flat and polypoid adenoma.
abstract: OBJECTIVE
  Several reports have suggested that flat colorectal adenomas might exhibit a higher potential for malignancy compared to polypoid adenomas. Although the clinical importance of the shape of polyps is stressed, the controversy surrounding the malignant potential of flat adenomas continues. The aim of this study was to compare the clinicopathologic characteristics, including degree of dysplasia and malignancy, between flat and polypoid adenomas 5 mm in size or larger.
  
  
  METHODS
  A total of 3263 polyps (254 flat adenomas and 3009 polypoid adenomas), >/=5 mm in size, diagnosed in 1883 patients by colonoscopy were analyzed.
  
  
  RESULTS
  Flat adenomas were found in 10% of patients, which represented 7.8% of all adenomas removed. The flat adenomas were larger in diameter than the polypoid adenomas (14.8+/-12.6 mm versus 8.6+/-5.0 mm, p <0.01), had a higher rate of villous components (18.5% versus 11.4%, p <0.01), a higher rate of high-grade dysplasia (9.4% versus 4.2%, p <0.01), and a higher rate of malignancy (10.2% versus 3.6%, p <0.01) than polypoid adenomas. However, there was no difference in the rate of high-grade dysplasia or carcinoma between flat and polypoid adenomas of equal size. It was shown by multivariate analysis that rectosigmoid location, larger size, and presence of a villous component were associated with a higher rate of malignancy, but not with flat morphology.
  
  
  CONCLUSIONS
  Flat adenomas, which were of a relatively large size in this study, were not associated with a higher risk for high-grade dysplasia and carcinoma compared with polypoid adenomas.
authors.affiliation: Departments of Internal Medicine, Institute of Gastroenterology, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Sang
authors.initials: S
authors.lastname: Kil Lee
authors.forename: Tae
authors.initials: T
authors.lastname: Il Kim
authors.forename: Sung
authors.initials: S
authors.lastname: Kwan Shin
authors.forename: Won
authors.initials: W
authors.lastname: Ho Kim
authors.forename: Hoguen
authors.initials: H
authors.lastname: Kim
authors.forename: Nam
authors.initials: N
authors.lastname: Kyu Kim
mesh_terms: D000236:Adenoma / Q000473:pathology*; D018256:Adenomatous Polyps / Q000473:pathology*; D000368:Aged; D000704:Analysis of Variance; D001707:Biopsy, Needle; D015331:Cohort Studies; D003111:Colonic Polyps / Q000473:pathology*; D003113:Colonoscopy / Q000379:methods; D015179:Colorectal Neoplasms / Q000473:pathology*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000473:pathology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011230:Precancerous Conditions / Q000473:pathology*; D011336:Probability; D012189:Retrospective Studies; D018570:Risk Assessment