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 remove polyps as small as one millimetre 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 is similar to, but not the same as, sigmoidoscopy—the difference being related to which parts of the colon each can examine. A colonoscopy allows an examination of the entire colon (measuring four to five feet in length). A sigmoidoscopy allows an examination of the distal portion (final two feet) of the colon, which may be sufficient because benefits to colonoscopy (cancer survival) have been limited to the distal portion of the colon.
The American Cancer Society "Guidelines for the Early Detection of Cancer" recommend, beginning at age 50, both men and women follow one of these testing schedules for screening to find colon polyps and cancer: 1. Flexible sigmoidoscopy every 5 years, or 2. Colonoscopy every 10 years, or 3. Double-contrast barium enema every 5 years, or 4. CT colonography (virtual colonoscopy) every 5 years.
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.