title: A prospective clinicopathological and endoscopic evaluation of flat and depressed colorectal lesions in the United Kingdom.
abstract: OBJECTIVE
  Flat and depressed colorectal lesions are now reported in Western populations. The malignant potential, anatomical distribution, and other clinicopathological features have not been established in this group. This study aimed to assess prospectively the prevalence, clinicopathological, and endoscopic features of flat and depressed colorectal lesions in the United Kingdom.
  
  
  METHODS
  A single endoscopist performed colonoscopy on 850 consecutive patients presenting for routine colonoscopy. All endoscopies were performed using a high magnification colonoscope with chromoscopy to facilitate detection of flat and depressed colorectal lesions.
  
  
  RESULTS
  A total of 458 flat lesions were identified. Of these, 173 (38%) were hyperplastic and 285 (62%) adenomatous or beyond. Of the 173 hyperplastic flat lesions, 162 (94%) were located in the recto-sigmoid region. Of the 267 adenomas, 66 (25%) had areas of high grade dysplasia (HGD), with 54/66 (82%) being present in the right colon. Flat lesions <8 mm in diameter was more likely to contain HGD than those <8 mm (p<0.001). Nine of the 10 (90%) flat invasive adenoacarcinomas were in the right colon and all had a depressed morphological component. In contrast, HGD was observed in 58/466 (12%) of protuberant (sessile/pedunculated) adenomas of which 95% (55/58) were located in the left colon. In addition, HGD was present in 17% of all sessile adenomas versus 44.6% of flat lesions >8 mm in diameter (p=0.001). Of the 14 protuberant carcinomas, 13/14 (93%) were in the left colon. Synchronous lesions were found in 96/816 (12%) of cases. Of the 816 patients with two or more left-sided protuberant adenomas <8 mm (with or without HGD), 89 (11%) had one or more flat lesions in the right colon with HGD.
  
  
  CONCLUSIONS
  Flat adenomas and carcinomas have a high malignant potential compared to protuberant lesions and have a propensity for developing in the right hemi-colon. Total colonoscopy is required to detect such lesions, as only 18% of flat lesions would be in reach of the flexible sigmoidoscope.
authors.affiliation: Gastroenterology and Liver Unit, and Academic Department of Surgery, Royal Hallamshire Hospital, Sheffield, United Kingdom.
authors.forename: David P
authors.initials: DP
authors.lastname: Hurlstone
authors.forename: Simon S
authors.initials: SS
authors.lastname: Cross
authors.forename: Ian
authors.initials: I
authors.lastname: Adam
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Shorthouse
authors.forename: Steven
authors.initials: S
authors.lastname: Brown
authors.forename: David S
authors.initials: DS
authors.lastname: Sanders
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Lobo
mesh_terms: D000328:Adult; D000368:Aged; D001707:Biopsy, Needle; D015331:Cohort Studies; D003113:Colonoscopy / Q000379:methods*; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000473:pathology*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011230:Precancerous Conditions / Q000473:pathology*; D011336:Probability; D011446:Prospective Studies; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D006113:United Kingdom / Q000453:epidemiology