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Digestive Disorders

2004 Edition

New Techniques for Imaging the Digestive Tract
A “video pill” and virtual colonoscopy appear to be more patient friendly than established diagnostic exams for viewing the intestines. But are they as good?

Combining state-of-the-art imaging and computer techniques, researchers have developed two new ways for gastroenterologists to view the small and large intestines. Patients can now swallow a video pill—a technique called capsule endoscopy—that produces images of the entire 20 feet of the small intestine. Another procedure, virtual colonoscopy, uses computed tomography or magnetic resonance imaging to view the large intestine (colon) noninvasively—that is, without having to insert a viewing tube through the rectum and up into the colon.

While at first glance these new techniques may appear to be improvements over endoscopy and colonoscopy, both have drawbacks that limit their widespread use. Nonetheless, capsule endoscopy appears to be useful for detecting problems that can’t be found with standard endoscopy. Virtual colonoscopy, however, appears to offer only limited advantages over standard colonoscopy for detecting colorectal cancer in most patients.

Capsule Endoscopy

Capsule endoscopy, approved by the U.S. Food and Drug Administration in 2001, has three main components. First is the capsule itself, which is somewhat larger than a vitamin pill (0.4 x 1 inches) and contains a video camera, light, battery, and radio transmitter. The capsule is swallowed, and it takes pictures of the small intestine as it passes through the gastrointestinal tract. The images are sent to the second component, an antenna and recording device about the size of a Walkman that is worn at the waist. The third component, a personal computer, is needed to download and view the images.

The Procedure. Capsule endoscopy requires some preparation beforehand. You may need to perform a bowel purge the night before using laxatives prescribed by your doctor, followed by a period of fasting. Alternatively, you may only need to fast for 8 to 12 hours before the procedure. On the day of the procedure, you will swallow the capsule with a glass of water. The capsule is then propelled through your gastrointestinal tract by rhythmic muscle contractions called peristalsis, which normally move food through the intestines.

The capsule takes pictures of the gastrointestinal tract, at a rate of two pictures per second. You can continue your normal daily activities, and you can begin to drink clear liquids two hours after swallowing the pill and can eat a light meal after four hours. You may be asked to keep a diary of everything you eat and drink and any symptoms you experience. The battery in the capsule wears out after about eight hours, and you will be asked to go back to your doctor around this time to return the recording device. The images are then downloaded and analyzed.

The capsule is not digested and passes intact through the digestive system and into your stool, usually within 24 hours. You do not need to return the capsule, but you should let your doctor know that it has passed out of your body. In general, no pain or discomfort is experienced with capsule endoscopy.

Benefits. For selected patients with symptoms that cannot be explained by the results of standard diagnostic techniques, capsule endoscopy appears to be a useful option and may reduce the need for exploratory surgery. It provides a complete view of the small intestine, particularly of areas that are usually unreachable with endoscopy or colonoscopy. Capsule endoscopy can shed light on bleeding, chronic abdominal pain or diarrhea, or malabsorption that might originate from the small intestine. For many patients, the procedure can pinpoint tumors and diagnose conditions like celiac disease or Crohn’s disease. A November 2002 study in the American Journal of Gastroenterology reported on 35 patients with unexplained gastrointestinal bleeding that was suspected to originate in the small intestine. In 63% of the cases, a diagnosis was made through capsule endoscopy.

Drawbacks. Capsule endoscopy is not a substitute for conventional endoscopy or any other diagnostic test of the esophagus, stomach, and duodenum. It should only be performed after an endoscopy is unable to provide an adequate explanation for symptoms. In addition, the capsule moves too fast through the esophagus to produce good images of this structure, and the stomach and large intestine are too big to view with the capsule. Also, doctors are unable to perform biopsies or stop bleeding as they can with conventional endoscopy.

One potential complication is not passing the capsule: It gets stuck in the intestines of about 1 in every 200 patients. To prevent this complication, you may need to have a barium swallow before capsule endoscopy to look for any narrowings or obstructions in the intestines where the capsule can get stuck. The risk of having the capsule become stuck is greater in people who have undergone gastrointestinal surgery or have a history of gastrointestinal obstruction (blockage).

Furthermore, capsule endoscopy may not be appropriate for people who have an implanted electrical device (such as a pacemaker), since it may interfere with the device’s electrical functioning.

Virtual Colonoscopy

Introduced in 1994, virtual colonoscopy has piqued the interest of lay people and health care professionals alike as a way to inspect the colon noninvasively. The technique involves computed tomography scanning or magnetic resonance imaging of the abdomen to create two- and three-dimensional images of the inside of the colon. Because only about 40% of people at risk for colon cancer undergo regular screening for the disease, some experts have proposed that a noninvasive virtual colonoscopy might be more acceptable to many people and would result in more people undergoing screening.

However, a great number of drawbacks to virtual colonoscopy make it an undesirable option for most people. First, a standard colonoscopy is still needed for confirmation of the diagnosis and biopsy if any abnormalities are detected. In one study, about two thirds of people who underwent virtual colonoscopy needed a subsequent standard colonoscopy because of abnormal findings. In addition, polyps cannot be removed during a virtual colonoscopy as they can during a standard one. Also, virtual colonoscopy cannot distinguish stool from polyps or malignant growths, leading to a large number of false-positive results (that is, the test indicates the presence of polyps or cancer when none really exists).

Furthermore, virtual colonoscopy requires a bowel purge the evening before, just like in standard colonoscopy. Many patients find the purge to be the worst part of a colonoscopy. And air is pumped into the colon just before a virtual colonoscopy, which can cause cramping. During a standard colonoscopy, patients are usually sedated and do not feel the cramping.

Last, virtual colonoscopy doesn’t always visualize the colon as well as a standard colonoscopy. One study found that virtual colonoscopy missed about 10% of the polyps found during standard colonoscopies and indicated trouble in 28% of cases when the standard colonoscopy was normal. While virtual colonoscopy can detect large growths almost as well as standard colonoscopy, it is not as good at detecting small polyps.

No medical organization recommends virtual colonoscopy as a screening method for colorectal cancer. However, the procedure may be appropriate for people who have medical conditions that make a standard colonoscopy risky or physically difficult.

The Bottom Line

Although capsule endoscopy doesn’t replace standard diagnostic procedures, it has proven useful in many cases where symptoms could not otherwise be explained. In addition, health insurance companies are beginning to recognize the utility of the procedure. Recently, six private insurance companies announced they will pay for it, and in some states, Medicare now reimburses certain patients who undergo the procedure. If insurance does not cover it, a capsule endoscopy can cost as much as $1,500. Insurance companies will likely not pay for a virtual colonoscopy, and the procedure will be useful only for a small subgroup of patients.


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Digestive Disorders

The Digestive Disorders White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Hopkins physicians.



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