What’s new in colonoscopy?
There are several new developments in colonoscopy. Most of these center around improving the detection of difficult-to-see lesions — small ones (for example, small polyps) and flat ones — as well as the ability to determine at the time of colonoscopy whether or not polyps and lesions need to be biopsied or removed because they may contain premalignant or malignant tissue. This is important because many of these lesions are not premalignant or malignant, and a lot of time and money is spent removing them and sending them for microscopic examination unnecessarily.
High-resolution images that allow better detection of flat lesions have become standard on most colonoscopes. Magnification of the images also may improve the detection of the lesions.
Narrow-band imaging uses a special wavelength of light that enhances the pattern of tiny blood vessels that lie just below the lining of the colon. The pattern of these vessels is different in normal, premalignant, and malignant tissue. Determination of the pattern allows lesions, particularly premalignant and malignant flat lesions, to be identified more easily and also allows a decision to be made as to whether or not the lesion should be biopsied or removed at the time of colonoscopy without waiting for the results of the microscopic examination.
Chromoendoscopy uses dyes (stains) that are sprayed on the colon lining to differentiate normal lining from neoplastic (benign, premalignant, and malignant) tissues and determine which lesions should be removed or biopsied.
Fluorescence endoscopy uses fluorescein-labeled chemicals either sprayed on the lining of the colon or injected intravenously. The chemicals are taken up by abnormal cells (premalignant and malignant) of the colon’s lining more than the normal cells, and special lighting makes the areas of abnormal cells clearer to see so they can be biopsied or removed completely. Confocal laser endoscopy uses a particular wavelength of light that penetrates the lining of the fluorescein-stained colon for several millimeters. Abnormal cells may be more clearly identified than with fluorescein staining alone.
There are even colonoscopes and accessories that allow a retrograde view of the colon in addition to the antegrade view from the tip of the colonoscope. Thus, images are obtained in two, 180 degree-opposed directions in order to identify lesions that might be hiding behind folds in the lining of the colon that would be missed by a standard, forward-viewing colonoscope. There are even attempts to develop a self-advancing colonoscope.
Most of these newer colonoscopic techniques, with the exception of high-resolution imaging, are not standard. Which one(s) will ultimately turn out to be valuable adjuncts to colonoscopy has yet to be determined.
Finally, magnetic resonance imaging (MRI) can be used to examine the colon in a manner similar to CT virtual colonoscopy. The major advantage of MRI is that there is no radiation exposure; otherwise, the limitations are similar to CT virtual colonoscopy.