A colonoscopy is an internal examination of the colon (large intestine) and rectum, using an instrument called a colonoscope. Although it is similar to sigmoidoscopy still it’s not exactly the same as that. A colonoscopy allows an examination of the entire colon (measuring four to five feet in length) where as sigmoidoscopy allows an examination of the distal portion (final two feet) of the colon only. Colonoscopy is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It may provide a visual diagnosis (e.g. ulceration, polyps) and grants the opportunity for biopsy or removal of suspected lesions. Colonoscopy can help to remove polyps as small as one millimeter or less. Once polyps are removed, they can be studied with the aid of a microscope to determine if they are precancerous or not.
Colonoscopy broadly includes virtual colonoscopy and standard colonoscopy and both have been always compared to determine which of the two is better. Whereas Virtual colonoscopy, which uses 2D and 3D imagery, reconstructed from computed tomography (CT) scans or from nuclear magnetic resonance (MR) scans is possible as a totally non-invasive medical test, it is not standard and still under investigation regarding its diagnostic abilities. Furthermore, virtual colonoscopy does not allow for therapeutic maneuvers such as polyp/tumor removal or biopsy nor visualization of lesions smaller than 5 millimeters. If a growth or polyp is detected using CT colonography, a standard colonoscopy would still need to be performed.
In the standard procedure, if the doctor sees any polyps, he or she can remove them, using a wire loop that passes through the tube. For this reason, the procedure carries a higher risk of bowel perforation. Virtual colonoscopy may suit a patient who experiences difficulty with the standard procedure, has an obstructed colon, is taking anti-coagulants, or is just unwilling to undergo the standard procedure. Earlier, virtual colonoscopy was not recommended for elderly people but now it can be said to be comparable to standard colonoscopy for people aged 65 and over. Virtual colonoscopy is as accurate as standard colonoscopy in its ability to accurately detect cancer and precancerous polyps. As a result the virtual colonoscopy could serve as an initial screening exam for colorectal cancer and can be effectively used in people belonging to all age groups.