|
Sigmoidoscopy.
Sigmoidoscopy involves using the sigmoidoscope, a metal or plastic tube 25 centimeters or 10 inches long, with a fiberoptic ring made of plastic light-conducting fibers that enables the doctor to see the tissues exposed at the end of the instrument
Ordinarily the patient has an enema with a phosphosoda solution an hour before the examination. During the actual examination, the patient may be lying in a facedown, kneeling position, or lying on his or her side on the examining table. A digital rectal examination should be performed first. Sigmoidos-copy, while not comfortable, should not be painful to the patient because the instrument is inserted very gently. Sometimes air may be forced into the opening to help expand the bowel walls to make it easier to pass the instrument through the large intestine and to examine the walls. During the examination, the wall of the rectum and lower portion of the sigmoid colon the S-shaped lower colon are examined. Any abnormal area should be biopsied; this is easily done since the instrument can be used to collect small amounts of tissue that later will be examined under the microscope. This can be done painlessly and with only brief, negligible bleeding from the biopsy site.
Flexible sigmoidoscopes have become available in the past few years. Longer than the rigid models—35 to 65 centimeters in length—they contain a flexible fiberoptic system that permits bending the instrument from the handle
The flexible sigmoidoscope is basically a recently developed, shortened version of the colonoscope, which can be as long as 165 centimeters or nearly five feet. The design and flexibility of these instruments permit the endoscopist, usually a gastroenterologist or surgeon trained in these examinations, to see and examine the entire length of the large bowel. Biopsies of abnormal or suspicious-looking areas can be taken easily through the colonoscope with a special biopsy tool. This examination is ordinarily performed as an outpatient procedure, but preparation is much more extensive than for sigmoidoscopy. Preparation before colonoscopy includes consuming a liquid diet and cleansing the bowel with laxatives and an enema.
The colonoscope has a number of uses other than visual examination and collection of tissue for biopsy. For example, polyps can be completely removed through the colonoscope, reducing the need for major abdominal surgery. Patients undergoing this procedure may be admitted to the hospital overnight, but the practice varies from doctor to doctor—many will send the patient home after a few hours of observation, since bleeding is the only significant complication and occurs only rarely.
Still another examination is the barium enema X ray. Barium sulfate, a contrast material that shows up on X-ray film, is introduced through the catheter inserted into the rectum. A series of X-ray films are then taken, the barium is withdrawn, and air is introduced into the rectum for a final set of X-ray pictures known as air-contrast studies. The air-contrast aspect of the barium enema study is important because this technique provides excellent X-ray images of the colon, including polyps. However, the barium enema examination with air contrast is not a substitute for rigid or flexible sigmoidoscopy or digital rectal examination, since the rectal channel is large and tumors in the lower rectum may be missed. As in the case with colonoscopy, a more extensive preparation is necessary for the barium enema. Packaged kits for bowel preparation for barium enema and endoscopic examinations are widely available at pharmacies, and the doctor performing the examinations will usually tell the patient what preparations are necessary and how to use them. Neither the barium enema nor the colonic endoscopy is dangerous or painful, although some mild discomfort may be felt with both examinations.
There is an ongoing controversy among scientists and physicians regarding the diagnostic value of the barium enema X-ray examination with air contrast as compared with colonoscopy. All physicians agree on the importance of air-contrast X-ray films as an integral part of the barium enema study. If it is well performed, a barium enema examination with air contrast will show all significant growths larger than one quarter of an inch. A well-performed colonoscopy will show even small growths, but there is about one chance in ten that the uppermost part of the large bowel, the cecum, will not be reached. A barium study is more widely available, less inconvenient for the patient, and much less costly than colonoscopy. Both are reasonably safe, but the barium enema is a little more so. In general, the resolution of which test to employ depends on the local skills available in radiology and endoscopy at the individual hospital.
Screening those persons without any symptoms of large bowel cancer is undoubtedly an effective measure in modern preventive medicine. There is good evidence from several different university research studies that early detection of colon cancer before the onset of signs and symptoms increases the chances for a cure. A Kaiser-Permanente study, for example, strongly suggested that early detection of large bowel cancer through the use of digital and sigmoidoscopic examination reduced the death rate from this disease in the population group studied. These results do not include any additional beneficial effect that the discovery and removal of adenomas may have had. Two other large studies showed excellent long-term survival rates for people with bowel cancer who were screened with sigmoidoscopy. About 90 percent of these patients survived fifteen or more years, a rate so much better than expected among 5 patients who did not undergo such screening that other factors are not likely to have biased the results.
These studies provide strong evidence that detection of large bowel cancer before symptoms appear greatly decreases the death rate from this disease, and that the benefits derived outweigh any cost involved. Indeed, they are highly cost-effective, since treating colon cancer or any cancer, for that matter in its early, most curable stages costs less, both in terms of money and human suffering, than treating advanced cancer.
|
