Synonyms and related keywords
colonoscopic examination, distal rectum, cecum, large bowel, adenomas, polyps, colorectal cancer, colon cancer, fecal occult blood testing, FOBT, polypoid lesions, barium enema, pseudopolyps, sigmoidoscopy, bowel resection, familial adenomatous polyposis, Gardner syndrome, ulcerative colitis, Crohn disease, hereditary nonpolyposis colorectal cancer, HNPCC, colitis, gastrointestinal bleeding, GI bleeding, colonoscope, polypectomy, inflammatory bowel disease, IBD, pancolitis, hydrostatic balloon dilatation, colonic strictures
Author: Jennifer Lynn Bonheur, MD , Staff Physician, Department of Internal Medicine, Lenox Hill Hospital
Jennifer Lynn Bonheur, MD, is a member of the following medical societies: American Association for the Advancement of Science, New York Academy of Sciences, and Sigma Xi Editor(s): Alex Jacocks, MD , Program Director, Professor, Department of Surgery, University of Oklahoma School of Medicine; Francisco Talavera, PharmD, PhD , Senior Pharmacy Editor, Pharmacy, eMedicine; Michael A Grosso, MD , Department of Cardiothoracic Surgery, St Francis Hospital; Alex J Mechaber, MD, FACP , Director of Clinical Skills Program, Assistant Professor, Department of Internal Medicine, Division of General Internal Medicine, University of Miami School of Medicine; and John Geibel, MD, DSc , Director, Professor, Departments of Surgery and Cellular and Molecular Physiology, Yale-New Haven Hospital, Yale University School of Medicine
Colonoscopy enables visual inspection of the entire large bowel from the distal rectum to the cecum. The procedure is a safe and effective means of evaluating the large bowel. The technology for colonoscopy has evolved to provide a very clear image of the mucosa through a videocamera attached to the end of the scope. The camera connects to a computer, which can store and print color images selected during the procedure. Compared with other imaging modalities, colonoscopy is especially useful in detecting small lesions such as adenomas; however, the main advantage of colonoscopy is that it allows for intervention, since biopsies can be taken and polyps removed.
Screening for and follow-up of colorectal cancer are among the indications for colonoscopy. Although colorectal cancer is highly preventable, it is still the second leading cancer killer in the United States. Proper screening can help reduce mortality rates at all ages, and colonoscopy plays an important role in this effort.
Surveillance of asymptomatic people of average risk older than 50 years
Recommendations vary among the leading organizations in this field, namely the American Cancer Society (ACS), the World Health Organization (WHO), the US Preventive Services Task Force (USPSTF), and the American College of Physicians (ACP). Only the ACP recommends colonoscopy (at 10-y intervals) for routine screening in asymptomatic patients. Others advise annual fecal occult blood testing (FOBT) and periodic flexible sigmoidoscopy with follow-up colonoscopy as indicated.
Further evaluation of polyps
The finding of a polyp larger than 1 cm in diameter during sigmoidoscopy is an indication for examination of the entire colon because 30-50% of these patients have additional polyps. Though controversy continues regarding whether colonoscopy is indicated for patients with a polyp(s) smaller than 1 cm, the general belief is that most cancers arise in preexisting adenomatous polyps, which should lead to a full colonoscopic examination, regardless of size.
Histologic diagnosis should be based on examination of the completely excised polyp. In general, all polypoid lesions greater than 0.5 cm in diameter should be totally excised. Polypoid lesions observed on barium enema may represent pseudopolyps, true polyps, or carcinomas. Colonoscopy can be used to differentiate among these and can similarly be used to distinguish between benign and malignant strictures, which cannot be accurately accomplished with radiologic studies alone.
If clinical signs and symptoms suggest colon cancer or when screening (by radiography or sigmoidoscopy) identifies a large bowel tumor, a full colonoscopic examination should be performed in order to take a biopsy and to search for synchronous lesions. Findings on colonoscopy may also have implications for the surgical treatment plan.
Personal history of prior adenomas or colon cancer
In patients with multiple benign polyps observed and removed on initial examination, a follow-up colonoscopy should be performed in 1 year to search for polyps missed on the initial examination. In patients with only one polyp observed and removed on initial examination, or if the first follow-up examination finding after multiple polypectomy is negative, the optimal follow-up interval appears to be every 3 years. If the colon is free of polyps, some authorities believe that a 5-year interval is safe.
Because of the potential implications for the operative plan, preoperative colonoscopy should be performed in patients who are to undergo bowel resection for colon cancer. Patients who have already had a large bowel cancer removed should have a colonoscopy performed 6 months to 1 year after surgery, followed by yearly colonoscopy on 2 occasions. Some authorities believe that colonoscopy should then be performed every 3 years if results of all these studies are negative.
Family history of cancer
Individuals with a family history of familial adenomatous polyposis or Gardner syndrome are recommended to undergo genetic testing and flexible sigmoidoscopy beginning at age 10-12 years. Consider total colectomy for these individuals because they have a nearly 100% risk of developing colon cancer by age 40 years. Colonoscopy is not as effective in preventing colon cancer under these circumstances as it is with polyps in general. Individuals with a first-degree relative diagnosed with colon cancer or adenomas when younger than 60 years, or with multiple first-degree relatives diagnosed with colon cancer or adenomas, should undergo screening colonoscopy every 3-5 years beginning at an age 10 years younger than the youngest affected relative.
The diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) should be considered in people who have several relatives with colorectal cancer, particularly if one or more of the relatives developed cancer when younger than age 50 years. These patients should be evaluated colonoscopically beginning at age 25 years or at an age 5 years younger than that of onset in the index case. Suggested follow-up care includes annual FOBT with colonoscopy every 2-3 years. Perform annual screening in patients older than 40 years.
Inflammatory bowel disease
Although many patients do not require colonoscopy for the diagnosis of inflammatory bowel disease, the procedure is an important aid in the follow-up care and management of patients with ulcerative colitis or Crohn disease. Colonoscopy is more sensitive than barium enema in determining the anatomic extent of the inflammatory process and is useful when clinical, sigmoidoscopic, and radiologic studies are inadequate. Colonoscopy with multiple biopsies is indicated to differentiate ulcerative colitis from Crohn disease.
The cancer surveillance schedule varies in patients with inflammatory disease. Patients with pancolitis for more than 7-10 years and patients with left-sided ulcerative colitis for more than 15 years are at an increased risk of developing colon cancer. The current recommendation for screening colonoscopy for these groups is every 1-2 years. For patients with Crohn disease of the colon, the same schedule of colonoscopic surveillance is warranted. Ideally, because differentiating inflammatory changes from premalignant ones can be difficult, colonoscopy for surveillance purposes should not be performed during periods of active colitis, and biopsies from areas of less inflammation should be preferred.
Colonoscopy has been recommended as the initial diagnostic test for patients with acute lower GI bleeding requiring fewer than 3 units of blood in the first 48 hours. If the bleeding source cannot be determined by colonoscopy, angiography may be required.
Guidelines for colonoscopy during pregnancy are not available because of insufficient data. The largest reported series included 8 colonoscopies performed during pregnancy. In this study, 6 patients delivered healthy infants after colonoscopy. One patient suffered a miscarriage unrelated to colonoscopy, and another had an elective abortion. In general, colonoscopy may be considered for severe life-threatening conditions during pregnancy when the only alternative is colonic surgery, or if colon cancer is suspected. The procedure is best performed in a hospital setting rather than in a doctor's office. Defer surveillance colonoscopy for prior history of cancer or polyps, abdominal pain, or change in bowel habits until the postpartum period.
The colonoscopy technique must be modified in a pregnant woman. To avoid uterine trauma, only minimal, if any, compression should be placed on the abdomen. Similarly, even if the study is difficult, pregnant women should never be placed in a prone position as may be done with nonpregnant patients. If the study is so difficult that this maneuver becomes necessary, the procedure should be stopped. Moreover, if sedation is to be used, diazepam should be avoided because of unconfirmed reports of teratogenicity. (Meperidine has a better-documented fetal safety profile than midazolam.) Fetal cardiac monitoring during the procedure should also be considered.
Discontinue warfarin, aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and iron supplements on the days prior to examination. Insulin should not be taken while fasting prior to colonoscopy. Foods to avoid on the day prior to the test include those that may be misinterpreted during examination (eg, red or purple foods, jello, or drinks). Patients should drink only clear liquids (no solid foods) on the day prior to colonoscopy and during the night before.
To maximize the thoroughness and safety of the procedure, the colon must be completely empty prior to colonoscopy. Several options are available for precolonoscopy bowel cleansing. The most commonly used preparations include (1) 1.5 ounces of Fleet Phospho-Soda liquid mixed into half a glass of water followed by a full glass of water at 3 pm and again at 7 pm on the day prior to examination or (2) 4 liters of polyethylene glycol (PEG) solution (eg, GoLYTELY, NuLYTELY, CoLyte) administered orally over a 1- to 3-hour period on the evening prior to colonoscopy.
Visicol is a new prescription laxative pill designed to cleanse the colon prior to colonoscopy. In a recent study by Aronchick et al, this tablet form of sodium phosphate was equally as effective and safe as the existing aqueous preparations. However, as with Fleet Phospho-soda, Visicol contains a high phosphate load that may not be safe for patients with kidney, heart, liver, or certain intestinal diseases.
Regardless of the laxative method used, note that patients must drink at least fourteen 8-ounce glasses of water or clear beverages during the day prior to colonoscopy to prevent dehydration.
According to the most recent American Heart Association recommendations (1997), the rate of bacteremia associated with colonoscopy is 2-5%, and the typically identified organisms are unlikely to cause endocarditis. The rate of bacteremia does not increase with mucosal biopsy or polypectomy. For this reason, prophylaxis for colonoscopy, with or without biopsy, is only recommended as optional for high-risk patients (eg, those with prosthetic valves, previous history of endocarditis, complex cyanotic congenital heart disease, surgically constructed pulmonary shunts/conduits, joint replacements); the need for prophylaxis must be determined on an individual basis by the physician. The most commonly used preprocedure and postprocedure prophylaxis regimens are ampicillin/amoxicillin (2 g IV/IM or 1.5 g PO), gentamicin (1.5 mg/kg), or vancomycin (1 g IV).
Administration of sedative drugs at colonoscopy has drawbacks, including an increased rate of complications, higher cost, and longer recovery periods for patients. Some studies have demonstrated that routine use of conscious sedation does not seem to be necessary because some participants found the examination to be only modestly or not at all uncomfortable. However, some investigators have proposed that without conscious sedation, the rate of intubation of the cecum may decrease and the risk of missing adenomas and cancer may increase.
Intravenous benzodiazepines are the usual premedications used for colonoscopy, either alone or with a narcotic. Midazolam (2-5 mg) and diazepam (5-10 mg) are most commonly used. Meperidine (25-100 mg) may be added as needed. The combination of benzodiazepines and narcotics may achieve sedation more smoothly but is associated with a greater risk of respiratory depression. Monitor patients (eg, blood pressure, pulse, oxygen saturation) for the duration of the procedure, and watch for adverse effects of these medications.
With the patient in left lateral decubitus position, a long, flexible, lighted viewing tube (colonoscope) is inserted through the rectum into the colon. The scope is advanced and maneuvered while the lumen and walls of the colon are visualized by projections onto a television screen. The colonoscope has channels through which instruments can be passed in order to perform biopsies, remove polyps, or cauterize bleeding. Air, water, and suction can be applied to help provide a clearer visual field for inspection. The goal for a complete examination is to reach the cecum and, in some cases, the terminal ileum. Landmarks that may help to determine if this has been achieved include visualization of the appendiceal orifice and the ileocecal valve. Transillumination above the right inguinal canal also suggests cecal intubation.
The alternative use of pediatric colonoscopes in adults has been studied. (Pediatric colonoscopes are thinner, more flexible, and, generally, shorter.) Employment of a pediatric colonoscope was found to be as successful as use of adult colonoscopes in performance of total colonoscopy in all outcome measures, including frequency of reaching the cecum, time needed to reach the cecum, total procedure time, endoscopists' perception of procedure difficulty, patients' assessment of comfort, and likelihood of need for a repeat examination in the future. Whether particular subgroups exist for whom the use of pediatric colonoscopes actually has an advantage compared to adult colonoscopes remains to be shown.
Investigators have also recently looked into colonoscopic withdrawal technique. A preliminary study by Rex associated higher-quality withdrawal techniques with lower miss rates for adenomas. In light of these findings, the suggestion has been made that withdrawal technique be subjected to further study and that standards for these techniques be developed.
Colonoscopy is generally a safe procedure and complications are rare.
The risk of perforation of the colon is 0.2-0.4% after diagnostic colonoscopy and 0.3-1.0% with polypectomy. A higher rate (4.6%) is associated with hydrostatic balloon dilatation of colonic strictures. Perforation is more common (1) in patients who are oversedated or under general anesthesia, (2) in the presence of poor bowel preparation, or (3) with acute bleeding, and generally results from mechanical or pneumatic pressure or from biopsy techniques.
Mechanical perforation by the tip of the instrument occurs at sites of weakness of the colon wall (eg, diverticula, transmural inflammation) and proximal to obstructing points (eg, neoplasms, strictures). Pneumatic perforation of the colon or ileum results from distension by insufflated air. Perforation from polypectomy is an electrosurgical injury.
Free perforation into the peritoneal cavity may be recognized during the procedure if abdominal viscera become visible. A laceration so large that it can be observed directly through the colonoscope is a surgical emergency. In less severe situations, marked persistent abdominal distension or pain should prompt the ordering of radiographs; this imagery may reveal free air in the peritoneum. These symptoms may be delayed for several days if the leak is tiny and well localized. Retroperitoneal perforation, usually a pneumatic injury, can give rise to subcutaneous emphysema. Fever and leukocytosis may eventually develop with any of these perforations. When plain abdominal or chest radiographs show pneumoperitoneum, gross extravasation should be assessed; if present, surgical intervention is required. In the absence of leakage, treatment with intravenous antibiotics and close observation may be considered. This is a clinical determination.
Bleeding complicates approximately 1 of every 1000 colonoscopic procedures. Most cases resolve spontaneously. Following polypectomy, bleeding may occur immediately, but, in 30-50% of cases, it is delayed from 2-7 days until the eschar sloughs. Immediate bleeding can be treated by resnaring the remaining stalk and tightening the snare for 10-15 minutes, usually without further electrocoagulation. Another procedure that may be helpful is the injection of 5-10 mL of a 1:10,000 epinephrine solution into the stalk or the submucosa to achieve vasoconstriction. Delayed bleeding usually stops spontaneously, although transfusions, endoscopic therapy, angiography, and even laparotomy may be required in more severe cases.
Documented instances of transmission of infection from one patient to another or to endoscopic personnel are extremely rare. Bacteria reported to have spread include Salmonella species, Pseudomonas species, and Escherichia coli . To date, no reports of transmission of hepatitis B or C or HIV have been made. Disinfection of scopes and accessories is the main preventive measure. Universal precautions against contact with patient's blood or bodily fluids should always be employed.
Colonic distension during colonoscopy can cause notable discomfort and may also impair mucosal blood flow. Carbon dioxide rather than air insufflation during colonoscopy may offer some advantages, ie, it is absorbed from the colon, it is nonexplosive, and mucosal blood flow is less affected, thus decreasing the risk of colonic ischemia.
Postpolypectomy coagulation syndrome
The combination of pain, peritoneal irritation, leukocytosis, and fever after colonoscopy may represent a postpolypectomy burn injury. A conservative approach generally leads to a good outcome.
Although a very uncommon complication, the presumed mechanisms of splenic rupture during colonoscopy include direct trauma to the spleen, marked angulation of the splenic flexure, excessive splenocolic ligament traction, and decrease in the relative mobility between the spleen and the colon. Hemodynamic instability, clinical features of acute abdomen, leukocytosis, and/or acute anemia in patients with persistent abdominal pain after colonoscopy demand immediate attention. Intestinal perforation or bleeding must first be excluded, after which CT scans can be used for further evaluation.
Small bowel obstruction
Small bowel obstruction is another rare complication of colonoscopy, although it is perhaps more common in patients who have a history of abdominal surgery and postoperative adhesions. The mechanism is uncertain, but it may occur secondary to air insufflation into the small bowel as a result of an incompetent ileocecal valve causing distension and entrapment of the small bowel by adhesions. Colonoscopists should be aware of this possible complication, particularly as skills improve and the ileum is intubated more frequently. Patients with a history of abdominal surgery or bowel obstruction should be informed of this complication when consent is given.
Sedatives used during colonoscopy may cause complications from allergic reactions or, more importantly, from doses that may be excessive for certain individuals and lead to respiratory depression. Serious events may complicate up to 0.5% of procedures. More than 50% of deaths associated with endoscopy are related to cardiopulmonary events.
Adverse effects of benzodiazepines, other than respiratory depression, include anxiety and occasional injection-site reaction; the latter are more frequent with diazepam than with midazolam. Other adverse effects of narcotics include nausea, vomiting, and hypotension. Naloxone and flumazenil readily reverse the adverse effects of narcotics and benzodiazepines, respectively, within minutes. The proper technique and sequence of administration of these drugs, together with continuous monitoring of the sedated patient, can help minimize complications.
Of patients with colorectal cancer, 2-9% have a second synchronous tumor and 27-53% have concomitant multiple adenomatous polyps. For this reason, a complete examination should be performed during colonoscopy. This entails full inspection from the rectum through the cecum, although this is not always possible. For example, stenosing tumors, acute diverticulitis, adhesions from previous pelvic surgery, postradiation stenosis, or strictures due to Crohn disease or ulcerative colitis can obstruct the lumen of the intestine and make it difficult for the endoscopist to reach the cecum. In some cases, a double-contrast barium enema is necessary to complete an examination, although this procedure is less sensitive than colonoscopy in detecting tumors and polyps.
Virtual colonoscopy, also known as CT colography, refers to using spiral CT scanning and computers to simulate colonoscopy by generating high-resolution multidimensional views of the colon.
As with traditional colonoscopy, the bowel must be prepared and cleared prior to the study. At the time of the CT scan, a rectal tube is inserted and the colon is filled with air. Intravenous glucagon may be used to relax the smooth muscle. The spiral CT scan is then performed (no contrast is needed), and a specialized computer is used to process the images obtained.
Virtual colonoscopy is less invasive than traditional colonoscopy and has the potential to be more accurate in determining the size, shape, and location of lesions. Suggested indications for this method include detection of polyps and carcinomas and staging of cancers. Some researchers have even suggested the possibility of someday being able to make tissue diagnoses based on certain numerical values.
Disadvantages include increased cost, possible increased discomfort (patients complain of more pain and discomfort during virtual colonoscopy than during endoscopic colonoscopy with conscious sedation), poor sensitivity for small polyps, and inability to accomplish biopsy or polyp removal, thus necessitating additional studies.
Still in the investigational stages are faster scanners with increased resolution and capabilities; researchers suggest the possibility of oral labeling agents that may eliminate the need for bowel cleansing. Virtual colonoscopy holds promise as a safe and relatively noninvasive addition to the future of colon imaging.
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