Colorectal cancer develops in approximately 5–6% of the adult population and is one of the leading causes of cancer death in Europe and the USA.^1,2 Screening colonoscopy is the widely accepted gold standard for early diagnosis of colorectal cancer and should be offered to patients older than 50 years.^3–5 However, colonoscopy is increasingly in competition with computed tomographic virtual endoscopy.⁶ Therefore, it is essential to understand whether total colonoscopy rather than virtual endoscopy enables the detection of all relevant premalignant and malignant lesions as only early diagnosis of neoplasias offers the possibility for curative endoscopic or surgical resection.

Polypoid lesions are easy to detect by endoscopy. In contrast, non-polypoid lesions are often overlooked.⁷ The endoscopist must be aware of flat and depressed lesions because the primarily visible mucosal changes of such lesions are often very discrete. In this context, the endoscopist should look for slight colour changes, interruption of the capillary network pattern, slight deformation of the colonic wall, spontaneously bleeding spots, shape changes of the lesion with insufflation or deflation of air, and interruption of the innominate grooves.⁷

An important diagnostic tool for detection of non-polypoid colorectal lesions consists of chromoendoscopy.⁸ In contrast with ulcerative colitis where pan-chromoendoscopy is favourable,⁹ targeted staining with indigo carmine or methylene blue in a selective fashion is sufficient for non-polypoid colorectal lesions.¹⁰ Chromoendoscopy helps to unmask such lesions in the colon and to delineate its borders. By the help of magnifying endoscope, the stained surface and crypt architecture can be analysed, and differentiation between non-neoplastic and neoplastic lesions becomes possible with high accuracy.¹¹ Recently, it was shown …