Colonoscopy Definition

An examination of the colon (also called bowel or large intestine) to detect and remove intestinal polyps, fleshy growths that may become cancerous, and to biopsy or remove small adenocarcinomas (cancerous polyps).

Conventional colonoscopy is an endoscopic procedure in which the gastroenterologist inserts a flexible, lighted tube (endoscope or colonoscope) through the anus and into the large intestine.

Reasons for Doing This Test

Colonoscopy is a diagnostic procedure to detect intestinal polyps, colorectal cancer, and other conditions affecting the colon.

Cancer experts believe screening colonoscopy, performed at age 50 (or earlier, when there is family history of colorectal cancer) and every 5 to 10 years thereafter, can prevent 80 to 90 percent of colorectal cancers.

Preparation, Procedure, and Recovery

The gastroenterologist performs conventional colonoscopy in an endoscopy center or hospital unit, with intravenous general sedation to minimize discomfort and anxiety. The procedure takes 30 to 45 minutes, with another one to two hours to recover from the sedation.

Colonoscopy Preparation

Most people find the preparation for colonoscopy, which consists of cleansing the gastrointestinal tract, the most unpleasant aspect of the procedure. The preparation for virtual colonoscopy requires the same bowel-cleansing procedure as does conventional colonoscopy. Completing the preparation for colonoscopy is essential for optimal results, however. It typically includes

  • no aspirin or aspirin products (to reduce the risk for bleeding) and no iron supplements or products (iron darkens tissue) for five days before the colonoscopy
  • no nuts, seeds, grapes, peas, beans, or tomatoes for three days before the colonoscopy (particles from these foods lodge in the folds of the intestinal mucosa)
  • no nonsteroidal anti-inflammatory drugs (nsaids) for five to seven days before the colonoscopy (to reduce the risk for bleeding)
  • only clear liquids for 24 hours before the colonoscopy
  • at midday the day before the colonoscopy, the bowel-cleansing process begins with the drinking of a laxative solution consumed at the rate of eight ounces every 10 minutes for a total consumption of one gallon of the solution

The laxative prep results in bowel movements that start about an hour after beginning to drink the solution and continue for about eight hours. Drinking the solution often causes nausea. Keeping the solution as cold as possible (even surrounding it with ice in the refrigerator) and chewing gum or sucking on hard candy between glasses can help.

It is necessary to drink the entire gallon of the solution to completely clear the gastrointestinal tract. Fecal remnants in the colon can obscure the wall of the bowel, limiting the ability of the gastroenterologist to visualize the entire colon. Most gastroenterologists will not proceed with the colonoscopy if the preparation is incomplete.

Colonoscopy Procedure

The person lies on his or her left side on a narrow bed, with the knees flexed. After initiating intravenous sedation, the gastroenterologist gently inserts the lubricated colonoscope into the anus. A small pump injects air ahead of the scope, opening the colon so the gastroenterologist can advance it into the colon.

The examination of the colon takes about 20 minutes, longer when there are polyps for the gastroenterologist to remove or biopsy. Some people feel pressure with the injection of air or when the scope rounds the corners of the colon. However, most people feel little discomfort and cannot recall the procedure when it is over.

Colonoscopy Recovery

Following conventional colonoscopy, the person rests in a recovery area until the sedative wears off, usually within an hour or two, and then may go home. Doctors recommend resting quietly for the remainder of the day, which is what most people feel like doing.

There is usually no discomfort after the procedure, aside from an accumulation of intestinal gas until regular eating returns the gastrointestinal tract to normal function. The gastroenterologist receives the pathologist’s analysis of any tissues removed within about a week. Following virtual colonoscopy, the person may go home immediately after the procedure.

Colonoscopy Risks and Complications

Complications related to conventional colonoscopy are very rare but may include perforated bowel (which requires emergency surgery to repair), infection, and bleeding from removed or biopsied polyps.

Virtual Colonoscopy

Virtual colonoscopy, a procedure that allows noninvasive visualization of the gastrointestinal tract, became available in the late 1990s. Virtual colonoscopy, correctly called computed tomography colonography or CT colonography, uses computed tomography (ct) scan to examine the colon with nearly the same accuracy as conventional colonoscopy but without the need for sedation or to enter the body.

The significant drawback to CT colonography is that it allows only viewing of the colon, not biopsy or polypectomy. The gastroenterologist must still use conventional colonoscopy to remove detected intestinal polyps or to biopsy suspicious growths. The preparation for virtual colonoscopy requires the same bowel cleansing procedure as does conventional colonoscopy.

Virtual colonoscopy does not require sedation. For the procedure, the radiologist inserts a small tube into the rectum for the injection of air to open the colon for improved visualization, which may cause discomfort that feels like intestinal gas. Over a period of 10 to 20 minutes the CT scanner takes sequential X-rays while the person lies on his or her back and then stomach. A computer compiles the X-rays to create three-dimensional images of the colon.


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