Colon Polyps (cont.)
Bhupinder Anand, MD
In this Article
How are colon polyps diagnosed?
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There are several means to diagnose colon polyps.
Endoscopic colonoscopy involves the use of a colonoscope, a flexible tube approximately five feet in length with a light and camera at the end and a hollow channel through which instruments can be passed. The colonoscope is passed via the anus into the colon and then through the colon until the proximal end of the colon - the cecum - is reached. On withdrawal of the colonoscope, the lining of the colon is observed for polyps and other abnormalities. These may be biopsied or removed using electro-cautery and then examined under the microscope. Colonoscopy identifies 95% of polyps, small and large, though occasionally polyps are missed if they are small, hidden by folds in the colon's lining, or the colonoscopy is hurried.
Virtual colonoscopy involves the use of either computerized tomography (CT) or magnetic resonance imaging (MRI). The colon is filled with either a liquid contrast agent or air, and CT or MRI is performed. Computerized reconstruction of either the CT or MRI images provides a virtual image that mimics the view obtained by a colonoscope. Virtual colonoscopy is very good at finding polyps but not as good as colonoscopy; it can miss polyps less than one centimeter in size, although the need to identify these smaller polyps is debated since they infrequently are malignant. MRI has an advantage over CT because of it does not expose the patient to radiation. It is more expensive, however, and there is less experience with MRI than with CT. The problem with both CT and MRI virtual colonoscopy is that if a polyp is found that should be removed, colonoscopy then must be done at a later time to remove it.
Barium enema is an older method of diagnosing colon polyps. During a barium enema, the colon is filled with barium, and multiple X-rays of the colon are taken as the patient changes position. Barium enema is a good way to diagnose polyps and is relatively inexpensive; however, it can easily miss small polyps and exposes patients to radiation. Moreover, the skills and experience necessary to do a barium enema properly have declined among radiologists because barium enemas are less frequently ordered now that colonoscopy and virtual colonoscopy are available. Finally, like virtual colonoscopy, if polyps are found, a colonoscopy must be done to remove the polyp.
Flexible sigmoidoscopy uses a shortened version of a colonoscope, approximately three feet in length. It is able to examine only the distal third to one-half of the colon. Like the colonoscope, it can be used to identify, biopsy, and remove polyps without exposure to radiation. For screening purposes, since the sigmoidoscope cannot examine the entire colon, it usually is combined with either less frequent colonoscopy or frequent stool occult blood tests to identify polyps beyond its reach.
Reviewed by Bhupinder Anand, MD on 3/15/2013
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