• indigo carmine
• dysplasia
• ulcerative colitis
• colonoscopy

Colonoscopy is the gold standard for colorectal cancer screening.^1–3 Detection and complete removal of adenomas disrupt the adenoma-carcinoma sequence and thus prevent the development of colorectal cancer. However, endoscopists still fear that they may have overlooked relevant lesions despite the availability of modern videoendoscopes. This problem is underlined by a relatively high rate of adenomas missed by conventional endoscopy (up to 27%), as determined by back to back or repeat colonoscopy studies.²³ Furthermore, retrospective analyses have suggested that colonoscopy may even fail to detect colorectal cancer (CRC),⁴⁵ although large multicentre studies indicated a high negative predictive value for a normal complete colonoscopy with regard to CRC (>99%).⁶ Therefore, the question arises of whether adenomas or CRC detected after previous colonoscopies have grown fast or were simply overlooked during initial endoscopic analysis?

Exophytic adenomas can be diagnosed easily and most of the Western endoscopists have previously focused on these polypoid lesions. In contrast, several years ago Japanese researchers described flat lesions in the colonic mucosa and classified these so-called “flat adenomas” as premalignant lesions.⁷⁸ These lesions now can be subdivided according to their growing pattern: small flat adenoma, lateral spreading adenoma, and depressed lesions with high malignant potential.⁷ It is well accepted that flat lesions show only small changes in the mucosal architecture, such as small depressions and discrete changes in colour. Detection of such subtle mucosal changes during conventional colonoscopy remained a challenge, even for experienced endoscopists. Recently, using dye spraying techniques, chromoendoscopy has revolutionised the detection of flat lesions in the colonic mucosa and, when used in a targeted …