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Small, depressed lesions of the large bowel: a normal finding at endoscopy
  1. J P MARTIN,
  1. Wolfson Endoscopy Unit
  2. St Mark’s Hospital
  3. Harrow
  4. Middlesex HA1 3UJ, UK
  5. Department of Gastroenterology
  6. The Christie Hospital
  7. Manchester M20 4BX, UK
  1. Dr Martin (email:johnpmartin{at}

Statistics from


Neoplastic large bowel lesions have been found that are flush with, or even depressed below, the colonic epithelium.1-5 These flat adenomas are reported to have an increased incidence of severe dysplasia when compared with polypoid lesions,1 ,4 ,6 ,7 and some have consisted exclusively of malignant cells. Thus, de novo development may be an alternative pathway of carcinogenesis.5 As a result, endoscopists are encouraged to be vigilant in discovering and removing these lesions. We report our experience of specific areas of normal depressed colonic mucosa that, macroscopically, have some features that are similar to true flat adenomas. Additionally, we suggest a way to distinguish these lesions from neoplastic lesions, thus avoiding unnecessary polypectomy.

Case histories

(1) An asymptomatic 57 year old woman with melanosis coli and an 8 mm constant depressed rectal lesion on flexible sigmoidoscopy; this was removed by submucosal saline injection and snare polypectomy. Histology showed melanosis coli only, and no evidence of neoplasia. (2) A 34 year old man with bloody diarrhoea, who underwent total colonoscopy and ileoscopy. The colonic mucosa was normal throughout, but in the rectum there was a 7 mm depressed lesion which was extensively biopsied (fig 1A). Histology was normal. (3) Another asymptomatic 57 year old woman with melanosis coli and an 8 mm depressed rectal lesion on flexible sigmoidoscopy. Multiple biopsy samples were taken which showed melanosis coli only. Two weeks later, the patient had a colonoscopy at which chromoscopy was performed. The endoscopist, who had performed the previous procedure, was unable to locate the lesion.

Figure 1

(A) Benign depressed lesion seen in case two. (B) True flat adenoma. Note the rough, reddened centre and irregular outline.

Trauma or suction had not been applied to the mucosa in any of these cases, and the depressions did not disappear on prolonged observation.


Flat or depressed colonic neoplasia were first described in 1985,1 and the development of high quality video colonoscopy and improved bowel preparation, has lead to the report of many more cases.8 These lesions seem to have a higher incidence of severe dysplasia than polypoid adenomas,1 ,4 ,6 ,7 and should be suspected whenever irregularities of the mucosal surface are seen.9 However, they may disappear on inflation of the bowel and, therefore, it is important to examine the mucosa carefully without excessive insufflation.10 The central depression is often rough and red when compared with the surrounding mucosa, and may appear as a plaque-like spot (fig 1B). Flat lesions should be treated by submucosal saline injection and mucosal resection, as this allows their complete removal and accurate histological assessment.9 ,11 ,12

Previously, flat depressed lesions have been confused with various benign pathologies,10 but this is the first report of normal histology in flat mucosal lesions. In our experience, when seen at endoscopy, flat lesions with a regular circular shape and normal central mucosa are likely to be of little significance, particularly if there is associated melanosis coli. In these cases diagnostic cold biopsy is appropriate, as well as tattooing the area for subsequent assessment. This practice will avoid unnecessary polypectomy and potential complications.


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