Colonoscopy is an endoscopic medical procedure that uses a colonoscope, a long, flexible, thin, lighted tube-like instrument containing a tiny video camera, that allows a visual examination of the lining of the colon (large intestine) and rectum.
A colonoscopy is generally recommended when the patient complains of rectal bleeding, has a change in bowel habits, and/or has other unexplained abdominal symptoms. The test is frequently used to look for colorectal cancer, especially when polyps or tumor-like growths have been detected by a barium enema examination and other diagnostic imaging tests. Polyps can be removed through the colonoscope, and samples of tissue (biopsies) can be taken to detect the presence of cancerous cells. In addition, colonoscopy can also be used to remove foreign bodies from the colon, control hemorrhaging, and excise tumors.
A colonoscopy allows the physician to visualize the lining of the entire colon and, therefore, it also enables physicians to check for bowel diseases such as ulcerative colitis and Crohn’s disease. Colonoscopy is being used increasingly as a screening tool in asymptomatic patients. It is recommended as a screening test in all people 50 years or older and is an essential tool for monitoring patients who have a past history of polyps or colon cancer.
Colonoscopy can be performed either in a physician’s office or in an endoscopic procedure room of a hospital or freestanding clinic. For otherwise healthy patients, colonoscopy is usually performed by a gastroenterologist or surgeon in an office or clinic setting. When performed on patients with other medical conditions that could cause complications or that require hospitalization, it is usually performed in the endoscopy department of a hospital, where more intensive physiologic monitoring and/or general anesthesia can be better provided.
An intravenous line is usually inserted into a vein in the patient’s arm to administer a sedative and a painkiller. During the colonoscopy, patients lie on their sides with their knees drawn up towards the abdomen. The doctor begins the procedure by inserting a lubricated, gloved finger into the anus to check for any abnormal masses or blockage. A thin, well-lubricated colonoscope is then inserted into the anus and gently advanced through the colon. The lining of the large intestine is examined through the colonoscope. The physician views images on a television monitor, and the procedure can be documented using a video recorder. Still images can be recorded and saved on a computer disk or printed. Occasionally, air may be pumped through the colonoscope to help clear the path or open the colon. If excessive secretions, stool, or blood obstructs the viewing, they are suctioned out through the scope. The doctor may press on the abdomen or ask the patient to change position in order to advance the scope through the colon.
The entire length of the large intestine can be examined in this manner. If suspicious growths are present, tiny biopsy forceps or brushes are inserted through the colon and tissue samples (biopsies) are obtained. Small polyps or inflamed tissue also can be removed using tiny instruments passed through the scope. For removing tumors or performing other types of surgery on the colon during colonoscopy, an electrosurgical device or laser system may be used in conjunction with the colonoscope. To stop bleeding in the colon, a laser, heater probe, or electrical probe is
used, or special medicines are injected through the scope. After the procedure, the colonoscope is slowly withdrawn and the instilled air is allowed to escape. The anal area is then cleansed with tissues. Tissue samples taken by biopsy are sent to a clinical laboratory, where they are analyzed by a pathologist.
The procedure may take anywhere from 30 minutes to two hours depending on how easy it is to advance the scope through the colon. Colonoscopy can be a long and uncomfortable procedure, and the bowel-cleansing preparation may be tiring and can produce diarrhea and cramping. During the colonoscopy, the sedative and the pain medications will keep the patient drowsy and relaxed. Some patients complain of minor discomfort and pressure from the colonoscope; however, the sedative and pain medication usually cause most patients to dose off during the procedure.
Patients who regularly take aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), blood thinners, or insulin should be sure to inform the physician at the time the colonoscopy is scheduled. The physician also should be notified if the patient has allergies to any medications or anesthetics, bleeding problems, or is pregnant. The doctor should be informed of all the medications the patient is taking and if he or she has had a barium enema x-ray examination recently. If the patient has had heart valves replaced, the doctor should be informed so that appropriate antibiotics
Barium enema— An X-ray test of the bowel performed after giving the patient an enema of a white chalky substance (barium) that outlines the colon and the rectum.
Biopsy— A procedure in which a sample of suspicious tissue is removed and examined by a pathologist for cancer or other disease.
Colonoscope— A thin, flexible, hollow, lighted tube that is inserted through the anus and rectum to the colon to enable the physician to view the entire lining of the colon.
Computed tomography (CT) scan— A radiologic imaging technique that uses computer processing to generate an image of the tissue density; also called computerized axial tomography (CAT) and computerized transaxial tomography (CTAT).
Crohn’s disease— A chronic inflammatory disease that generally starts in the gastrointestinal tract and causes the immune system to attack one’s own body.
Diverticulosis— A condition that involves the development of sacs that bulge through the large intestine’s muscular walls, but are not inflamed. It may cause bleeding, stomach distress, and excess gas.
Electrosurgical device— A medical device that uses electrical current to cauterize or coagulate tissue during surgical procedures; often used in conjunction with laparoscopy.
Magnetic resonance imaging (MRI)— A test that provides pictures of organs and structures inside the body using radio waves. In many cases, an MRI provides information that cannot be obtained from X-ray tests.
Pathologist— A doctor who specializes in the diagnosis of disease by studying cells and tissues under a microscope.
Polyps— An abnormal growth that develops on the inside of a hollow organ such as the colon.
Sigmoidoscopy— A process of passing a long, hollow tubular instrument through the anus in order to permit inspection, diagnosis, treatment, and imaging, especially of the sigmoid flexure.
Ulcerative colitis— A chronic condition in which recurrent ulcers are found in the colon. It is manifested clinically by abdominal cramping and rectal bleeding.
Virtual colonoscopy— Two new techniques that provide views of the colon to screen for colon polyps and cancer. The images are produced by computerized manipulations rather than direct observation through the colonoscope; one technique uses the X-ray images from a CT scan, and the other uses magnetic images from an MRI scan.
can be administered to prevent infection. Patients with severe active colitis, extremely dilated colon (toxic megacolon), or severely inflamed bowel may not be candidates for colonoscopy. Patients requiring continuous ambulatory peritoneal dialysis are generally not candidates for colonoscopy due to a higher risk of developing internal bleeding. The risks associated with the procedure are explained to the patient beforehand, and the patient is asked to sign a consent form.
The colon must be thoroughly cleansed before performing colonoscopy. Consequently, for about two days before the procedure, considerable preparation is necessary to clear the colon of all stool. The patient is asked to refrain from eating any solid food for 24–48 hours before the test. Only clear liquid such as juices, broth, and gelatin are allowed. Red or purple juices should be avoided, since they can cause coloring of the colon that may be misinterpreted as blood during the colonoscopy. The patient is advised to drink plenty of water to avoid dehydration. A day before the
colonoscopy, the patient is prescribed liquid, tablet, and/or suppository laxatives by the physician. In addition, commercial enemas may be prescribed. The patient is given specific instructions on how and when to use the laxatives and/or enemas. This preparatory emptying of the colon assures that the colonoscope will not be obstructed and that the physician will be able to clearly see the colon lining.
On the morning of the colonoscopy, the patient is not to eat or drink anything. Unless otherwise instructed by the physician, the patient should continue to take all current medications. Vitamins with iron, iron supplements, or iron preparations should be discontinued for a few weeks before the colonoscopy because iron residue in the colon can inhibit viewing during the procedure. These preparatory procedures are extremely important to ensure a thoroughly clean colon for examination.
After the procedure, the patient is kept under observation until the medications’ effects wear off.
The patient has to be driven home and can generally resume a normal diet and usual activities unless otherwise instructed. The patient is advised to drink plenty of fluids to replace those lost by laxatives and fasting.
For a few hours after the procedure, the patient may feel groggy. There may be some abdominal cramping and a considerable amount of gas may be passed. If a biopsy was performed or a polyp was removed, there may be small amounts of blood in the stool for a few days. If the patient experiences severe abdominal pain or has persistent and heavy bleeding, this information should be brought to the physician’s attention immediately.
The procedure is practically free of complications and risks. Rarely, (two in 1,000 cases) a perforation (hole) may occur in the intestinal wall. Heavy bleeding due to the removal of the polyp or from the biopsy site occurs infrequently (one in 1,000 cases). Some patients may have adverse reactions to the sedatives administered during the colonoscopy, but severe reactions are very rare. Infections due to a colonoscopy are also extremely rare. Patients with artificial or abnormal heart valves are usually given antibiotics before and after the procedure to prevent an infection.
The results are normal if the lining of the colon is a pale reddish pink and there are no abnormal masses visible. In this case, the patient probably will not have to undergo another colonoscopy for several years.
Abnormal results indicate polyps or other suspicious masses in the lining of the colon. Many polyps can be removed during the procedure, and tissue samples can be taken by biopsy. If cancerous cells are detected in the tissue samples, then a diagnosis of colon cancer is made. A pathologist analyzes the tumor cells further to estimate the tumor’s aggressiveness and the extent of the disease. This is crucial before deciding on the mode of treatment for the disease. Abnormal findings could also be due to inflammatory bowel diseases such as ulcerative colitis or Crohn’s disease. A condition called diverticulosis, which causes many small finger-like pouches to protrude from the colon wall, may also contribute to an abnormal result in the colonoscopy.
Colorectal cancer is the second leading cause of cancer deaths in the United States. In 2007, The American Cancer Society estimated that 52,180 people died from the disease. The World Health Organization (WHO) estimates that about 500,000 people world-wide die from colorectal cancer each year. Although colonoscopy screening can find precancerous growths (polyps), which lead to colorectal cancer, screening rates in the United States remain low. Removing polyps before they become cancerous can prevent the disease and potentially reduce deaths. Scientific evidence indicates that more than one-third of deaths from colorectal cancer could be avoided if people aged 50 years and older were screened regularly.
Individuals with a strong family history of colorectal cancer may wish to undergo genetic screening to detect a genetic alteration that may identify people who are more likely to develop the disease and who would benefit from earlier and more frequent screening. Only about 5% of colorectal cancers are inherited, so genetic testing provides limited benefits for most of the population.
Virtual colonoscopy is a new non-invasive technique for screening for colon polyps and cancer. The colon is cleaned out using potent laxatives just as it is for a standard colonoscopy. Instead of obtaining pictures through the insertion of a colonoscope, virtual colonoscopy uses X-ray images from a computerized tomography (CT) scan or magnetic resonance imaging (MRI) to create through computer manipulation two- and three-dimensional pictures of the colon.
Virtual colonoscopy offers several advantages. The procedure is non-invasive. It does not require patients to be sedated or put under anesthesia and is a good option for individuals who cannot or will not undergo standard colonoscopy. The procedure can be performed in less than one minute, compared with about 30-60 minutes plus recovery time required for standard colonoscopy. Another benefit of the CT scan is that it can find polyps that occasionally are missed by colonoscopy because the polyps lie behind folds within the colon.
Disadvantages of virtual colonoscopy include:
- It has difficulty finding small polyps (<0.2 in [5 mm] in size) that are easily seen in a colonoscopy.
- It is less able to find flat polyps compared to a colonoscopy.
- Small pieces of stool can look like polyps on the CT scan and lead to a diagnosis of polyp when there is none.
- It is not possible to remove suspect polyps or take a biopsy. If polyps are found by virtual colonoscopy, a standard colonoscopy must be done to remove the polyps. As a result, the individual must undergo two procedures.
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American College of Gastroenterology, P.O. Box 342260, Bethesda, MD, 20827-2260, (301) 263-9000, http://www.acg.gi.org.
Colorectal Cancer Network (CCNetwork), P.O. Box 182, Kensington, MD, 20895-0182, (301) 879-1500, http://clickonium.com/colorectal-cancer.net/html/.
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Jennifer E. Sisk, M.A.
Crystal H. Kaczkowski, M.Sc.
Tish Davidson, A.M.