colonoscopy
Meaning of colonoscopy: The only bowel test that both finds a polyp and removes it, which is why it prevents cancer rather than merely detecting it.
Definition of colonoscopy
Colonoscopy is an examination of the inside of the large bowel with a colonoscope, a flexible tube carrying a light, a camera and channels for instruments. Passed through the rectum and advanced to the far end of the colon, it lets the operator inspect the lining, take samples and remove polyps in the same session, usually under sedation.
What happens during the procedure?
Preparation matters more than the examination itself. The bowel has to be completely empty, which means a period of clear fluids and a strong laxative preparation beforehand, because residue hides exactly the small flat lesions the test exists to find. Sedation or light anesthesia is usual. The instrument is passed through the rectum and steered around the bends of the colon to the cecum, where the small intestine joins, and often a short way into the last part of the small intestine. Gas opens the bowel for viewing, and carbon dioxide is now preferred because it is absorbed quickly and leaves less bloating afterward. Most of the careful inspection happens as the instrument is slowly withdrawn. A colon polyp can be lifted and cut off with a wire snare, and tissue can be sampled anywhere along the way.
How does it compare with other bowel tests?
| Test | How far it reaches | Can it treat? |
|---|---|---|
| Colonoscopy | The whole colon | Yes: biopsy and polyp removal |
| Flexible sigmoidoscopy | Rectum and lower colon only | Yes, within that reach |
| CT colonography | The whole colon, by imaging | No; findings require a colonoscopy afterward |
| Stool tests | Detect blood or DNA markers, not the bowel itself | No; a positive result leads to colonoscopy |
A sigmoidoscopy needs less preparation and often no sedation, but it cannot see disease beyond its reach, which is the trade-off.
What are the risks and limits?
Bleeding is the most common complication and follows polyp removal rather than inspection. Perforation of the bowel wall is uncommon but serious and may require surgery. Sedation carries its own small risks, particularly for people with heart or lung disease. The test is not perfect: lesions hidden behind folds or lying flat against the wall can be missed, and the quality of the preparation and the care taken on withdrawal both affect how much is found. Because removing a polyp interrupts the slow sequence by which some polyps become colon cancer, the procedure prevents disease as well as diagnosing it, which is what separates it from a test that only reports.
Used in a sentence
A colonoscopy was scheduled to further evaluate the cause of the patient's rectal bleeding.
Good to know
A colonoscopy examines the entire colon, while a sigmoidoscopy is limited to its lower portion, a distinction that affects which conditions each procedure can reliably detect.
Word origin
Where “colonoscopy” comes from
Formed from colon, from Greek kolon, combined with -scopy, from Greek skopein, meaning to look at or examine.