A procedure in which a doctor looks inside the entire colon (large intestine) using a special scope. Colonoscopy is used to diagnose the causes of unexplained changes in bowel habits and to screen for abnormal tissue. It can detect the early signs of colorectal cancer, which struck an estimated 139,500 Americans in 2002 (the most recent year for which statistics are available) and resulted in as many as 56,600 deaths.
During colonoscopy, a person lies on his left side on the examining table. Usually, pain medicine and a mild sedative are given. The doctor inserts a colonoscope — a long, flexible tube with a light and a tiny video camera — into the rectum and guides it into the colon. The colonoscope bends so that the doctor can guide it around the curves in the intestine. The physician can get a clear, detailed image of the bowel on a TV monitor and check it for abnormal growths, ulcers, bleeding, and muscle spasms.
With colonoscopy, the doctor may detect abnormal growths called polyps on the inside of the intestine. Most polyps are not cancerous, but some are, and it is impossible to tell whether a polyp is cancerous or potentially cancerous just by looking at it. Using tiny instruments passed through the colonoscope, the doctor can remove a polyp (a procedure called polypectomy). The polyp can then be tested in the laboratory to determine whether it is cancerous.
Other colorectal screening methods include a fecal occult blood test (looking for hidden blood in the stool), flexible sigmoidoscopy (an examination of only the lower part of the colon), and a barium enema (in which a thick barium solution is pumped into the bowel through an enema tube and then an x-ray is taken). Gastrointestinal specialists are still debating the relative merits of the various screening procedures and exactly what role colonoscopy should play.
The American Cancer Society (ACS) currently recommends that men and women age 50 and older should have a fecal occult blood test every year, along with a flexible sigmoidoscopy every five years. Having a double-contrast barium enema every five years or a colonoscopy every 10 years are other options. All positive tests (tests in which polyps or other irregularities are found) should be followed up with a colonoscopy for confirmation. The ACS recommends that high-risk individuals, such as those with a family history of colon cancer or an inflammatory bowel disease, be tested earlier and more regularly.