colon cancer symptom : Endoscopy

Endoscopy is an examination of internal structures using a flexible viewing tube (endoscope). When passed through the mouth, an endoscope can be used to examine the esophagus (esophagoscopy), the stomach (gastroscopy), and most of the small intestine (upper gastrointestinal endoscopy). When passed through the anus, an endoscope can be used to examine the rectum (anoscopy); the lower portion of the large intestine, the rectum, and the anus (sigmoidoscopy); and the entire large intestine, the rectum, and the anus (colonoscopy). For procedures other than anoscopy and sigmoidoscopy, the person is given medication intravenously to prevent discomfort.

Endoscopes range in diameter from about ¼ inch to about ½ inch and range in length from about 1 foot to about 5 feet. The choice of endoscope depends on which part of the digestive tract is to be examined. The endoscope is flexible and provides both a lighting source and a small camera, which allows doctors to get a good view of the lining of the digestive tract. The doctor can see areas of irritation, ulcers, inflammation, and abnormal tissue growth.

Many endoscopes are equipped with a small clipper with which tissue samples can be taken. These samples can then be evaluated for evidence of inflammation, infection, or cancer. Because the lining and the inner layers of the walls of the digestive tract do not have nerves that sense pain (with the exception of the lower part of the anus), this procedure is painless.

Endoscopes can also be used for treatment. A doctor can pass different types of instruments through a small channel in the endoscope. An electric probe at the tip of the endoscope can be used to destroy abnormal tissue, to remove small growths, or to close off a blood vessel. A needle at the tip of the endoscope can be used to inject drugs into dilated veins in the esophagus and stop their bleeding.

Before having an endoscope passed through the mouth, a person usually must avoid food for several hours. Food in the stomach can obstruct the doctor's view and might be vomited up during the procedure. Before having an endoscope passed into the rectum and colon, a person usually takes laxatives and is sometimes given enemas to clear out any stool. In addition, the person must avoid food for several hours before the procedure because it might be vomited up and because it would reduce the effectiveness of the laxatives and enemas.

Complications from endoscopy are relatively rare. Although endoscopes can injure or even perforate the digestive tract, they more commonly cause only irritation of the digestive tract lining and a little bleeding.

http://www.merck.com/mmhe/sec09/ch119/ch119c.html#sec09-ch119-ch119c-141