Chromoendoscopy

Widespread application of dye to the lumen of the colon (pan-chromoendoscopy) improves the detection of diminutive lesions (Brown, Baraza & Hurlstone 2007) (I). However, pan-chromoendoscopy is time consuming and the extra lesions detected may be unimportant clinically as a significant number of diminutive lesions may regress (Rother, Knopfle & Bohndorf 2007). The authors of a recent Cochrane review concluded that selective application of dye to suspicious areas (selective chromoendoscopy) may be more appropriate during colonoscopy

This approach is consistent with the conclusions of a recent international workshop which reviewed the role of non-polypoid lesions in the aetiology of colorectal cancer. The endoscopist should be skilled in recognising subtle changes in the appearance of the mucosal surface, particularly alterations in colour, vascularisation and morphology, to identify suspicious areas requiring dye spraying and to better detect polypoid lesions. Small patches of mucus may require rinsing to expose underlying suspicious areas worthy of staining, particularly in the right colon 

Selective chromoendoscopy with dye spraying on the lesion has been shown to be superior to conventional colonoscopy predicting polyp histology (Pohl et al. 2008) (III). Magnification chromoendoscopy is more effective than conventional chromocolonoscopy for diagnosing neoplastic colorectal polyps (Emura et al. 2007)

Expert opinion (VI) suggests that selective chromoendoscopy facilitates: 

•  assessment of the lesion and its borders; 
•  excision of the lesion and of residual tissue; 
•  colonoscopy for patients with chronic inflammatory bowel disease; and 
•  colonoscopy for high-risk family syndromes such as HNPCC.  

Thus for most polypoid and non-polypoid colorectal abnormalities, a flexible high-definition video endoscope and the facility for selective application of dye (chromoscopy) to the lesion is currently sufficient for detection and characterisation of high-risk lesions. It is recommended that all but the smallest flat or sessile lesions be ‘lifted’ with submucosal injection of saline or colloid to facilitate safe removal (endoscopic mucosal resection). Lesions that do not ‘lift’ should not be removed because they are more likely to be malignant, and removal is more likely to lead to perforation