Dye application technique
The first part of the colonoscopy involves inserting the endoscope until it reaches the terminal section of the colon (caecum). A spray catheter is inserted into the endoscope’s instrument channel and the product is sprayed when the endoscope is removed. The endoscope is then inserted once more up to the caecum. The intestinal lining is closely examined as the endoscope is slowly removed.
Colonoscopy is currently the most reliable exam (more complicated but more precise than Hemoccult®) for the detection and treatment of precancerous lesions of the colon, whether they are precancerous polyps or Lynch syndrome (hereditary colorectal cancer without polyps). Indigo carmine helps determine the nature of a polyp and detect degeneration in an adenomatous polyp.
“Indigo carmine is especially useful, once a lesion has been detected, for determining its lateral extent, if it is not clear from standard endoscopy. Indigo carmine can also be used to detect residual adenomatous tissue on the edges of a mucosectomy. During the mucous resection of a flat lesion over two centimetres in size, indigo carmine dyeing is recommended to determine the edges of the lesion before the resection and to look for residual lesions after the resection. Dyeing is also recommended if there is any doubt” (http://www.fmcgastro.org).
By accentuating contour, 0.2% indigo carmine can detect elevated or irregular areas that may represent foci of degeneration.
There are two kinds of chemical dyes: surface dyes, which do not penetrate cells, but increase contour (indigo carmine), and vital dyes, which penetrate certain kinds of cells, thereby revealing them. Certain vital dyes are merely absorbed or diffused (Lugol, methylene blue, toluidine blue, gentian violet), while others trigger chemical reactions producing a characteristic colour (phenol red, Congo red).
Virtual colouring can be obtained using two methods: by shining a certain wavelength of light on the tissue, which reveals components within the tissue which react to this wavelength (autofluorescence) or absorb the wavelength (Narrow Band Imaging), or by changing the signal obtained under traditional white light (FICE system). (http://www.fmcgastro.org).