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 can provide a visual diagnosis (e.g., ulceration, polyps) and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions.

Colonoscopy can remove polyps smaller than one millimeter. Once polyps are removed, they can be studied with the aid of a microscope to determine if they are precancerous or not. It can take up to 15 years for a polyp to turn cancerous.

Colonoscopy is similar to sigmoidoscopy—the difference being related to which parts of the colon each can examine. A colonoscopy allows an examination of the entire colon (1200–1500 mm in length). A sigmoidoscopy allows an examination of the distal portion (about 600 mm) of the colon, which may be sufficient because benefits to cancer survival of colonoscopy have been limited to the detection of lesions in the distal portion of the colon.

A sigmoidoscopy is often used as a screening procedure for a full colonoscopy, often done in conjunction with a fecal occult blood test (FOBT). About 5% of these screened patients are referred to colonoscopy.

Virtual colonoscopy, which uses 2D and 3D imagery reconstructed from computed tomography (CT) scans or from nuclear magnetic resonance (MR) scans, is also possible, as a totally non-invasive medical test. Virtual colonoscopy does not allow therapeutic maneuvers such as polyp and tumour removal or biopsy, nor visualization of lesions smaller than 5 millimeters; if a growth or polyp is detected using CT colonography, it would require removal during a standard colonoscopy. Surgeons have used the term pouchoscopy to refer to a colonoscopy of the ileo-anal pouch.

About 1 in 200 people who undergo a colonoscopy experience a serious complication. Perforation of the colon occurs in about 1 in 2000 procedures, bleeding in 2.6 per 1000, and death in 3 per 100,000,with an overall risk of serious complications of 0.35%.

In some low-risk populations screening by colonoscopy in the absence of symptoms does not outweigh the risks of the procedure. For example, the odds of developing colorectal cancer between the ages of 20 and 40 in the absence of specific risk factors are about 1 in 1,250 (0.08%).

The rate of complications varies with the practitioner and institution performing the procedure, and other variables.

The pain associated with the procedure is not caused by the insertion of the scope but rather by the inflation of the colon in order to do the inspection. The scope itself is essentially a long, flexible tube about a centimeter in diameter, i.e. as big around as the little finger, which is less than the diameter of an average stool.

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Journal of Inflammatory Bowel Diseases and Disorders

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