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By Walter W. Chan, MD, MPH, Assistant Professor of Medicine, Harvard Medical School; Director, Center for Gastrointestinal Motility, Division of Gastroenterology, Hepatology, and Endoscopy, Brigham and Women's Hospital

Endoscopy is an examination of internal structures using a flexible viewing tube (endoscope). Endoscopy can also be used to treat many disorders because doctors are able to pass instruments through the tube. When passed through the mouth, an endoscope can be used to examine the esophagus (esophagoscopy), the stomach (gastroscopy), and part 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, people are given drugs by vein (intravenously) to calm them and prevent discomfort (sedation). People who are having endoscopy of the upper parts of the digestive tract are given a liquid or spray anesthetic to numb their throat.

Viewing the Digestive Tract With an Endoscope

A flexible tube called an endoscope is used to view different parts of the digestive tract. The tube contains several channels along its length. The different channels are used to transmit light to the area being examined, to view the area through a camera lens (with a camera at the tip of the tube), to pump fluids or air in or out, and to pass biopsy or surgical instruments through. When passed through the mouth, an endoscope can be used to examine the esophagus, the stomach, and some of the small intestine. When passed through the anus, an endoscope can be used to examine the rectum and the entire large intestine. Different endoscopes are used for different procedures, and the tubes vary in length and size.

Endoscopes range in diameter from about ¼ inch (a bit more than ½ centimeter) to about ½ inch (1¼ centimeters) and range in length from about 1 foot (about 30½ centimeters) to about 6 feet (almost 2 meters). 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 digestive tract lining. The doctor can see areas of irritation, ulcers, inflammation, and abnormal tissue growth. Some endoscopes have ultrasound probes on the tip. Images from these probes can show details that ultrasound probes placed on the person's skin cannot.

Doctors can use endoscopes to screen people for certain disorders, such as colon cancer, or to screen people who are a certain age. For example, people who are age 50 and older should undergo colonoscopy every 10 years (or more frequently if they have had polyps in the colon or have a family history of colon cancer) to detect polyps or other changes.

Many endoscopes are equipped with a small clipper with which tissue samples can be taken (endoscopic biopsy). These samples can then be evaluated for 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 can be used to inject drugs into dilated veins in the esophagus and stop their bleeding. A laser mounted at the end can be used to destroy abnormal tissue.

Before having an endoscope passed through the mouth, a person must avoid food for 6 to 8 hours and avoid liquids for 4 hours before the procedure. Food in the stomach can block 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 because it would reduce the effectiveness of the laxatives and enemas.

Complications resulting from endoscopy are relatively rare, and most are related to the drugs used for sedation. Although endoscopes can injure or even perforate the digestive tract, they more commonly cause irritation of the tract lining and a little bleeding.

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