Colonoscopy is an endoscopic medical procedure that uses a long, flexible, lighted tubular instrument called a colonoscope to view the rectum and the entire inner lining of the colon (large intestine).
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, control hemorrhaging, and excise tumors.
The test also enables physicians to check for bowel diseases such as ulcerative colitis and Crohn's disease and is an essential tool for monitoring patients who have a past history of polyps or colon cancer. Colonoscopy is being used increasingly as a screening tool in both asymptomatic patients and patients at risk for colon cancer. It has been recommended as a screening test in all people 50 years or older.
Colonoscopy can be performed either in a physician's office or in an endoscopic procedure room of a hospital. For otherwise healthy patients, colonoscopy is generally performed by a gastroenterologist or surgeon in an office setting; when performed on patients with other medical conditions requiring hospitalization, it is often 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 inserted into a vein in the patient's arm to administer, in most cases, a sedative and a painkiller.
During the colonoscopy, patients are asked to 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 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 out. 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 observed, tiny biopsy forceps or brushes can be inserted through the colon and tissue samples can be obtained. Small polyps or inflamed tissue can be removed using tiny instruments passed through the scope. For excising 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 prior to the colonoscopy. 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 intraperitoneal bleeding.
The physician 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 can be administered to prevent infection. The risks 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 two or more 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 during the colonoscopy. The patient is advised to drink plenty of water to avoid dehydration. A day or two 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.
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. However, vitamins with iron, iron supplements, or iron preparations should be discontinued for a few weeks prior to 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.
For patients with abnormal results such as polyps, the gastroenterologist will recommend another colonoscopy, usually in another year or so.
The procedure is virtually free of any complications and risks. Rarely, (two in 1,000 cases) a perforation (a 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 masses that appear abnormal in the lining.
Abnormal results indicate polyps or other suspicious masses in the lining of the intestine. 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.
Morbidity and mortality rates
In 2003, an estimated 57,100 people will die from colorectal cancer. Although screening could find precancerous growths (polyps), which lead to colorectal cancer, screening rates in the United States remain low. Removing polyps before they turn into cancer could prevent the disease and potentially reduce deaths. Scientific evidence shows that more than one-third of deaths from colorectal cancer could be avoided if people aged 50 years and older were screened regularly.
Despite recent advances in screening and treatment for colon cancer, it is still one of the most common cancers among men and women in the United States. According to a report in the American Journal of Gastroenterology, there has been no improvement in colon cancer survival in the United States since the 1980s. As well, the number of patients surviving five years after their cancer diagnosis did not improve.
Recent National Cancer Institute-funded clinical trials show that taking daily aspirin for as little as three years could reduce the development of colorectal polyps by 19–35% in people at high risk for colorectal cancer.
The Center for Disease Control and Prevention recommends that everyone 50 years of age and over have one or a combination of the four recommended screening tests: fecal occult blood test, sigmoidoscopy , colonoscopy, or barium enema.
New research suggests that a simple blood test may identify people at risk of colorectal cancer. The blood test detects a genetic alteration that may identify people who are likely to develop the disease and who would benefit from additional screening; however, further research has to be done before this test becomes available.
Virtual colonoscopy is a new technique under development and evaluation for screening for colon polyps and cancer, and is undergoing continual improvement. One technique uses images from a magnetic resonance imaging (MRI) scan, and the other uses the x-ray images from a computerized tomography (CT) scan. They both provide views of the colon that are similar to those obtained in a colonoscopy. The images of the colon are produced by computerized manipulations rather than direct observation through the colonoscope.
While the CT scan technique is available in many radiology units, the MRI scan technique is still experimental. The colon is cleaned out using potent laxatives for both types of studies. A virtual image of the colon is formed after the scans are performed, and the images are analyzed and manipulated.
One 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. Nevertheless, criticisms of the CT scan include:
- It cannot find 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.
- The procedure does not require patients to be sedated or put under anesthesia, and it can be performed in less than one minute, compared with about 30–60 minutes, plus recovery time required for standard colonoscopy.
- Small pieces of stool can look like polyps on the CT scan and lead to a diagnosis of polyp when there is none.
- If colonic polyps are found by virtual colonoscopy, then standard colonoscopy must be done to remove the polyps. As a result, the individual must undergo two procedures.
Although the CT scan is a good option for individuals who cannot or will not undergo standard colonoscopy, it has not been determined if it should be a primary screening tool for individuals at either normal risk or high risk for polyps or cancer.
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Jennifer E. Sisk, MA Crystal H. Kaczkowski, MSc