Updated: Feb 04, 2022
Author: David E Stein, MD, MHCM; Chief Editor: John Geibel, MD, MSc, DSc, AGAF 



Colonoscopy enables visual inspection of the entire large bowel (also called the colon or large intestine) from the distal rectum to the cecum. It remains the gold standard for the detection of polyps and colorectal cancer. 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 video camera attached to the end of the scope. The camera connects to a computer, which can store and print color images selected during the procedure.

Screening for and surveillance of colorectal cancer are among the indications for colonoscopy. Although colorectal cancer is highly preventable, it remains the second most common cause of cancer death in the United States. Both men and women face a lifetime risk of nearly 6% for the development of invasive colorectal cancer. Proper screening can help reduce mortality at all ages, and colonoscopy plays an important role in this effort.

Endoscopists should, when assigning appropriate screening and surveillance intervals, follow current guidelines. Repeat colonoscopy should be performed in 3 years on all patients with advanced adenomas. If, in average-risk patients, screening colonoscopies are normal or only small distal hyperplastic polyps are present, repeat examinations should not be performed before 10 years.[1]

Compared with other imaging modalities, colonoscopy is especially useful in detecting small lesions (eg, adenomas) that can develop into cancer; however, its main advantage is that it also allows for intervention, because biopsies and polypectomies can be performed.

See Benign or Malignant: Can You Identify These Colonic Lesions?, a Critical Images slideshow, to help identify the features of benign lesions as well as those with malignant potential.


Screening, evaluation, and follow-up of colorectal cancer

Screening in average-risk adults

Recommendations for colorectal cancer screening vary among the leading organizations in this field—namely, the American Cancer Society (ACS),[2, 3] the World Health Organization (WHO), the US Preventive Services Task Force (USPSTF), and the American College of Physicians (ACP), and the American Gastroenterological Association (AGA).[1] It is generally now recommended, however, that average-risk adults should begin colorectal cancer screening at age 45 years. There are a few approved screening options, of which colonoscopy every 10 years is the most common in the United States.

Other tests that screen for colon cancer include annual fecal occult blood testing (FOBT) and fecal immunohistochemical testing (FIT), as well as stool DNA testing (multitarget DNA testing). Barium enema is rarely performed today; newer modalities, such as computed tomography (CT) colonography, have gained wider acceptance.

Evaluation and removal 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. Although controversy continues regarding whether colonoscopy is indicated for patients with a polyp or polyps 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.

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.

When 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 to obtain biopsy samples and to search for synchronous lesions. Findings on colonoscopy may also have implications for the surgical treatment plan.

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. After a large (>2 cm) sessile polyp has been removed or if there is concern that an adenoma was not completely excised, repeat colonoscopy should generally be performed in 3-4 months. If residual tissue remains, it should be resected and colonoscopy repeated again in another 3-4 months.

In patients with polyps identified on initial examination, the American Cancer Society recommends that follow-up colonoscopy be performed on the basis of polyp number and type, as well as dysplasia grade, as follows[2] :

  • Patients with small rectal hyperplastic polyps can be treated as patients with an average risk of cancer, with colonoscopy or other screening on a similar schedule

  • Individuals with one or two sub-1-cm tubular adenomas with low-grade dysplasia should receive colonoscopy 5-10 years after polyp removal

  • Patients who have three to 10 adenomas or one adenoma larger than 1 cm or who have any adenomas with high-grade or villous features should receive follow-up colonoscopy 3 years after removal

  • Patients who have more than 10 adenomas on initial examination should undergo colonoscopy within 3 years

  • Patients with sessile adenomas that are removed in pieces should undergo follow-up colonoscopy 2-6 months after removal

Current or previous bowel resection for colon cancer

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 two occasions. Some authorities believe that colonoscopy should then be performed every 3 years if the results of all these studies are negative.

Family history of cancer

Individuals with a family history of familial adenomatous polyposis (FAP) or Gardner syndrome are recommended to undergo genetic testing and flexible sigmoidoscopy or colonoscopy every 12 months, beginning at age 10-12 years until age 35-40 years if negative. 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 who have a first-degree relative diagnosed with colon cancer or adenomas when younger than 60 years, or who have multiple first-degree relatives diagnosed with colon cancer or adenomas, should undergo screening colonoscopy every 3-5 years, beginning either at age 40 years or at an age 10 years younger than that of the earliest familial diagnosis, whichever comes first.[4]

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 50 years. HNPCC is an autosomal dominant disorder with an approximately 70% lifetime risk of developing colorectal cancer.

These patients should be evaluated colonoscopically every 1-2 years, beginning at age 20-25 years or at an age 10 years younger than that of onset in the index case (whichever comes first). Perform annual screening in patients older than 40 years.

Management of inflammatory bowel disease

Although many patients do not require colonoscopy for the diagnosis of inflammatory bowel disease (IBD), the procedure is an important aid in the follow-up care and management of patients with ulcerative colitis or Crohn disease (see the images below). 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.

Inflammatory bowel disease. Severe colitis noted d Inflammatory bowel disease. Severe colitis noted during colonoscopy. Mucosa is grossly denuded, with active bleeding noted. Patient had her colon resected very shortly after this view was obtained.
Colonoscopy. Ulcerative colitis as visualized with Colonoscopy. Ulcerative colitis as visualized with colonoscope.
Colonoscopy. Colonoscopic image of large ulcer and Colonoscopy. Colonoscopic image of large ulcer and inflammation of descending colon in 12-year-old boy with 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-side 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. It has been suggested that as many as 64 biopsies are needed to achieve 95% sensitivity in surveying for dysplasia in patients with IBD.

Newer technologies, including chromoendoscopy, magnification endoscopy, and narrow-band imaging, may improve detection of dysplasia during surveillance colonoscopy and allow endoscopists to take fewer but higher-yield biopsies.

For additional information on these topics, see Ulcerative Colitis, Inflammatory Bowel Disease, and Crohn Disease.

Identification and treatment of acute bleeding sites

In the case of lower gastrointestinal (GI) bleeding, colonoscopy can be useful not only for localizing the site of bleeding but also, potentially, for enabling therapeutic intervention. Endoscopic therapy using injection of epinephrine, electrocauterization, argon plasma coagulation (APC), band therapy, and/or clips can be used to treat various causes of lower GI bleeding, including postpolypectomy coagulation syndrome, diverticula, arteriovenous malformations (AVMs), hemorrhoids, and radiation-induced mucosal injury.

In the acute setting, the endoscopist may be limited by poor visualization in an unprepared colon and by the risks of sedation in an acutely bleeding patient. A purge preparation may be considered, using 4 L of polyethylene glycol (eg, GoLYTELY, CoLyte) either orally over 2 hours or via a nasogastric tube, as tolerated by the patient.

If the bleeding source cannot be determined by means of colonoscopy, angiography or a nuclear medicine scan may be required. Radiographic studies should be performed before colonoscopy when perforation or obstruction is suspected.

Decompression of colon

A volvulus is a twist of a segment of intestine, most commonly in the sigmoid colon and cecum, which often causes a bowel obstruction and can lead to ischemia. Patients present with abdominal pain, nausea/vomiting, obstipation, and abdominal distention. Surgical intervention is generally recommended for a cecal volvulus. Colonoscopy/sigmoidoscopy can be used to decompress the colon in the case of sigmoid volvulus by advancing the endoscope through the torsed segment of bowel. A large expulsion of air indicates a successful reduction.

Acute colonic pseudo-obstruction (Ogilvie syndrome) is a clinical condition characterized by signs and symptoms of an acute large-bowel obstruction in the absence of a mechanical cause. When supportive treatment fails, endoscopic decompression may be considered to prevent bowel ischemia and perforation. This is a technically difficult procedure and should be performed by using minimal air insufflation and without preceding oral laxative preparation.

Whereas colonoscopy appears to be beneficial in the management of patients with Ogilvie syndrome, it is associated with a greater risk of complications, and randomized trials have not been done to establish its efficacy.


Pregnancy is considered to increase the risk of colonoscopy. Guidelines for colonoscopy during pregnancy are not available, because of insufficient data. The largest reported series included eight colonoscopies performed during pregnancy. In this study, six 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 when 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.

Other relative contraindications for colonoscopy include known or suspected colonic perforation, toxic megacolon, and fulminant colitis or severe IBD with ulceration; these conditions increase the risk of perforation.[5]

Technical Considerations

Best practices

For a colonoscopy to be effective, the bowel preparation (cleansing) must be adequate,[6] or visualization suffers. Preprocedural patient instructions are important to ensure good colon preparation. Numerous regimens exist today, but polyethylene glycol (PEG) is still the most cost-effective preparation. PEG is an osmotic laxative and works by causing watery diarrhea so that the stool can be emptied from the colon. The medication also contains electrolytes to prevent dehydration and other serious side effects that may be caused by fluid loss as the colon is emptied.

Bowel preparation quality should be measured by endoscopy units, on a unit level, at least annually. Screening and surveillance colonoscopies should be associated with adequate bowel preparation (ie, a Boston Bowel Preparation Scale [BBPS] score ≥6, with each segment score ≥2) in at least 90% of procedures, with the aspirational target being 95% or above.[1]

In patients undergoing colonoscopy, split-dose bowel preparation should serve as the endoscopy unit's standard preparation strategy.[1]

High-definition colonoscopes should be used by endoscopy units for screening and surveillance colonoscopy.[1]

Many patients choose to have anesthesia for their colonoscopy. This can take the form either of conscious sedation with midazolam and fentanyl or moderate sedation handled by means of anesthesia.

Inflating the colon with air to facilitate visualization of the mucosa simulates abdominal cramps and can be uncomfortable.

The patient is most commonly positioned in the left lateral decubitus position. A digital rectal examination is mandatory. The scope is inserted gently and then advanced to the cecum. The cecum can be identified by three landmarks: the cecal strap, the appendiceal orifice, and the ileocecal valve. If it is difficult to identify one of the landmarks, transillumination (visualizing the light of the scope in the right lower quadrant) can be used as an aid for determining the location. The endoscopist should photographically document the cecum with a landmark.

The American Gastroenterological Association colonoscopy clinical practice guidelines include the following recommendations[1] :

  • To improve polyp detection, endoscopists should give the right colon a second look, either in retroflexed or forward view.

  • Endoscopy units should, at the endoscopist and unit level, routinely measure the adenoma detection rate and provide feedback on it, doing so at least annually or when 250 screening colonoscopies have been accrued by the endoscopists.

  • Individual endoscopists should have a goal adenoma detection rate of 30% or above, with the aspirational target being at least 35%. When these thresholds are not met, endoscopists "may consider extending withdrawal times, self-learning regarding mucosal inspection and polyp identification, peer feedback, and other educational interventions."

  • Serrated lesion detection rates should be measured by endoscopy units on an endoscopist and unit level, with the unit providing feedback on these values. For serrated lesion detection, an individual endoscopist should have a goal rate of 7% or higher, with the aspirational target being at least 10%. Low rates should be addressed with improvement efforts oriented toward colonoscopists and pathologists.

  • For nonpedunculated polyps 3-9 mm in size, cold snare polypectomy should be employed, with aim taken at "a small rim of normal tissue around the polyp." Polyps that are over 2 mm in size should generally not be addressed with forceps.

  • If overt malignant endoscopic features are not present and patient pathology is not consistent with invasive adenocarcinoma, individuals with complex polyps should be evaluated by an expert in polypectomy with regard to the use of endoscopic resection.

Withdrawal time should exceed 6 minutes so as to maximize the rate of polyp detection. Using minimal air during advancement keeps the colon length short and makes the procedure more comfortable for the patient.

Water immersion colonoscopy and water exchange colonoscopy are two newer techniques that use water instead of air. Use of these techniques results in less colon distention and more comfort and can enhance visualization.

Complication prevention

Several organizations and authors have made recommendations for safe colonoscopy during the COVID-19 pandemic.[7] The European Centre for Disease Prevention and Control (ECDC) has recommended using a filtering face piece of respiratory class 2 or 3, goggles or a face shield to protect the eyes, and long-sleeved water-resistant gowns and gloves. Use of a class 2 or 3 filtering face piece is recommended during interrogation and when the colonoscopy report is being written.


Colonoscopy is safe and effective and rarely leads to complications. There is a real risk of colon injury during the procedure,[8] but with only about one in 1750 cases resulting in perforation, colonoscopy is, on the whole, extremely safe. Currently, more aggressive techniques of polyp removal, such as endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD), are becoming more widely performed; these are associated with a higher rate of colonic perforation than routine screening is.


Periprocedural Care

Preprocedural Planning

Bowel preparation

To maximize the thoroughness and safety of colonoscopy, the colon must be completely empty before the procedure. Several options are available for precolonoscopy bowel cleansing. The most commonly used preparations are as follows:

  • 1.5 oz of Fleet Phospho-Soda liquid mixed into half a glass of water, followed by a full glass of water at 3:00 PM and again at 7:00 PM on the day prior to examination
  • 4 L of polyethylene glycol (PEG) solution (eg, GoLYTELY, NuLYTELY, CoLyte) administered orally over a 1- to 3-hour period on the evening prior to colonoscopy

A reduced-volume lavage regimen comprising 2 L of PEG solution plus four delayed-release 5-mg bisacodyl tablets (HalfLytely) was introduced in an effort to improve patient compliance. DiPalma et al found that this preparation was as effective as a standard 4-L PEG solution but had fewer reported adverse effects.[9] HalfLytely has been discontinued from the US market.

Several low-volume colon cleansing preparations are available with various options for dosage regimens (eg, evening before procedure, split dose, early morning before procedure)., Examples include sodium picosulfate/magnesium oxide/anhydrous citric acid (Clenpiq), sodium sulfate/magnesium sulfate/potassium chloride (Sutab), sodium sulfate/potassium sulfate/magnesium sulfate (Suprep), and two formulations of PEG/electrolytes/sodium ascorbate/ascorbic acid (MoviPrep, PlenVu).

The stimulant laxative activity of sodium picosulfate, coupled with the osmotic laxative activity of magnesium citrate (formed from magnesium oxide and citric acid components after mixing with water), produces a purgative effect, which, when these substances are ingested with additional fluids, produces watery diarrhea.

Approval of this preparation for use in the United States was based on data from two pivotal phase III noninferiority studies comparing it with the reduced-volume lavage regimen described above.[10, 11] In both studies, Prepopik achieved successful colon cleansing according to the Aronchick scale, demonstrating noninferiority to the comparator. Additionally, it demonstrated statistical superiority in cleansing of the colon as compared with the control preparation.

MiraLax with Gatorade is a low-volume bowel preparation regimen that has been used widely in community practice and has been reported by patients to be better tolerated than GoLYTELY. A 2012 study demonstrated that bowel preparation with MiraLax in Gatorade was as efficacious as using GoLYTELY and that split dosing was more effective than single dosing.[12] MiraLax was better tolerated and improved the patient experience. Given the anecdotal evidence suggesting that patients consider bowel preparation the worst part of a colonoscopy, it is possible that achieving equivalent cleansing with an easier preparation will eventually lead to better compliance with colonoscopy screening.

Visicol is a prescription laxative pill designed to cleanse the colon prior to colonoscopy. In a study by Aronchick et al, this tablet form of sodium phosphate was as effective and safe as the existing aqueous preparations.[13] However, like Fleet Phospho-soda, Visicol contains a high phosphate load that may not be safe for patients with kidney, heart, liver, or certain intestinal diseases.

Concerns have been raised about the risk for developing renal insufficiency after the use of oral sodium phosphate solution (Fleet Phospho-soda) or Visicol in patients without a history of underlying renal disease or a recognized contraindication to the usage of oral sodium phosphate preparation.

A trigger for these concerns was a study by Markowitz et al that identified 31 cases of nephrocalcinosis among 7349 native kidney biopsy samples processed from 2000 through 2004.[14] Of these patients, 21 presented with acute renal failure and had a history of recent colonoscopy preceded by bowel cleansing with oral sodium phosphate solution (Fleet Phospho-Soda) or Visicol. The average baseline creatinine was 1.0 mg/dL prior to colonoscopy.

At follow-up, four patients went on to require permanent hemodialysis, and the remaining 17 all developed chronic renal insufficiency (mean serum creatinine, 2.4 mg/dL).[14] The authors suggested that potential etiologic factors included inadequate hydration during colon preparation, increased patient age, a history of hypertension, and concurrent use of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker.

Regardless of the laxative method used, it should be kept in mind that to prevent dehydration, patients must drink at least 14 8-oz glasses of water or clear beverages during the day prior to colonoscopy.

It is not uncommon for patients to report being unable to tolerate the colon-cleansing preparation, often secondary to the unpalatable taste and large volume of the preparation, the occurrence of nausea and vomiting, or the presence of abdominal cramping and bloating. If the patient reports already passing clear liquid stool, discontinuance of further preparation may be considered.

The author frequently recommends placing the PEG preparations in the refrigerator 1 day before use or adding sugar-free flavor packets (eg, Crystal Light) in an effort to improve the palatability of the PEG solution. Prepopik should not be prepared in advance or refrigerated before use. Ensuring that patients ingest the cleansing agent at a particular rate is not as critical as determining that they have ingested the entire volume of the agent to ensure evacuation.

Antibiotic prophylaxis

The 1997 American Heart Association (AHA) recommendations stated that the rate of bacteremia associated with colonoscopy is 2-5% and that the typically identified organisms are unlikely to cause endocarditis.[15] The rate of bacteremia does not increase with mucosal biopsy or polypectomy.

The 2007 updates to the AHA recommendations stated that there is no role for antibiotic prophylaxis to prevent infective endocarditis from colonoscopy.[16] In high-risk patients (eg, those with prosthetic valves, a previous history of endocarditis, complex cyanotic congenital heart disease, surgically constructed pulmonary shunts or conduits, or joint replacements), the need for antibiotic prophylaxis should be determined by the physician on an individual basis. The most commonly used preprocedure and postprocedure prophylaxis regimens are as follows:

  • Ampicillin or amoxicillin, 2 g IV/IM or 1.5 g orally
  • Gentamicin, 1.5 mg/kg
  • Vancomycin, 1 g IV

Patient Preparation


Colonoscopies are routinely performed with the use of sedative medications. 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.

IV benzodiazepines have been 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.

Propofol, a short-acting IV sedative, has become more commonly used during colonoscopies. It provides no analgesia but leads to a deeper level of sedation with rapid onset and shorter recovery time in comparison with conventional narcotic-benzodiazepine combinations. Propofol is generally administered by an anesthesiologist present at the time of the colonoscopy. Patients must be monitored (eg, blood pressure, pulse, oxygen saturation) for the duration of the procedure, as well as observed for adverse effects of these medications.

Warfarin, aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and iron supplements should be discontinued on the days prior to examination. Insulin should not be taken during precolonoscopy fasting. Foods to avoid on the day prior to the test include those that may be misinterpreted during examination (eg, red or purple foods, Jell-O, or drinks). Patients should drink only clear liquids (no solid foods) on the day before colonoscopy and during the night before.


The procedure is performed with the patient in the left lateral decubitus position.



Standard Colonoscopy

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 means of 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. (See the videos below.)

Colonoscopy. Colonoscopy video shows narrowed area in colon in setting of diverticulitis. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video shows narrowed area in colon in setting of diverticulitis. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video shows diverticulosis (pockets within colon that can bleed or become infected). Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video shows removal of large polyp by hot snare polypectomy technique. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video shows removal of small polyp from cecum with snare polypectomy technique. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video shows pseudopolyps in colon. This is usually seen in inflammatory bowel disease (eg, Crohn disease or ulcerative colitis). Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video shows mass in colon suspicious for colon cancer. Mass is too large to remove endoscopically and will have to be tattooed so that surgeons can find it easily. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video shows placement of tattoo adjacent to colon mass in order to make it visible and easy to locate for surgeons. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Colonoscopy. Colonoscopy video depicts arteriovenous malformation (AVM) in colon. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.

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. The goal for a complete examination is to reach the cecum and, in some cases, the terminal ileum (see the images below). Landmarks that may help in determining whether this has been achieved include visualization of the appendiceal orifice and the ileocecal valve. Transillumination above the right inguinal canal also suggests cecal intubation.

Colonoscopy. Stricture in terminal ileum noted dur Colonoscopy. Stricture in terminal ileum noted during colonoscopy. Narrowed segment visible upon intubation of terminal ileum with colonoscope. Relatively little active inflammation is present, indicating that this is cicatrix stricture.
Colonoscopy. Inflammation in terminal ileum noted Colonoscopy. Inflammation in terminal ileum noted during colonoscopy. Areas of inflammation, friability, and ulceration in terminal ileum are consistent with mild-to-moderate Crohn disease.

Full inspection from the rectum through the cecum 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, though this procedure is less sensitive than colonoscopy in detecting tumors and polyps.

Additional considerations

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 over the use of adult colonoscopes remains to be determined.

Investigators have also looked into colonoscopic withdrawal technique. A study by Rex associated higher-quality withdrawal techniques with lower miss rates for adenomas.[17] In view of these findings, it has been suggested that withdrawal technique should be subjected to further study and that standards for these techniques should be developed.

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 does.) Fetal cardiac monitoring during the procedure should also be considered.

Alternative Approaches to Colonoscopy

Virtual colonoscopy

Virtual colonoscopy, also known as computed tomography (CT) colonography, refers to the use of spiral CT 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 before 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. Spiral CT is then performed (without any need for contrast), 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 on the basis of 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. In addition, computer-aided polyp detection systems as an adjunct to virtual colonoscopy are being studied for their ability to increase sensitivity for smaller polyps. Virtual colonoscopy holds promise as a safe and relatively noninvasive addition to the future of colon imaging.

Colon capsule endoscopy

Wireless capsule endoscopy (using a pill-sized capsule containing a wireless video camera that transmits images to a small recording device) is an accepted means for endoscopically visualizing the small bowel. Clinical trials have suggested that colon capsule endoscopy may be a safe alternative for patients unable or unwilling to undergo conventional or virtual colonoscopy.[18, 19]

High-definition colonoscopy

High-definition colonoscopy may provide better detection of colorectal polyps than traditional colonoscopy does.[20, 21]

In a retrospective study, Buchner et al compared high-definition colonoscopy (n = 1204) with standard white-light colonoscopy (n = 1226) for the detection of adenomas.[20] The investigators found that the adenoma detection rate and the polyp detection rate were higher among patients who underwent high-definition colonoscopy, which they concluded could reduce the number of missed adenomas and the subsequent risk for colorectal cancer.[20]

In a prospective, randomized study assessing colonoscopy with a high-definition wide-angle endoscope (n = 193) against colonoscopy using a standard colonoscope (n = 197) for the detection of polyps, Tribonias et al found significant differences between the two methods with respect to both the overall rate of polyps detected and the rate of small (< 5 mm) hyperplastic polyps detected; however, they found no differences between the two techniques regarding large (≥10 mm), medium-sized (5-10 mm), and small (< 5 mm) polyps.[21]

Tribonias et al also found no significant differences between high-definition, wide-angle endoscope and standard colonoscope for the detection rate of adenomas and hyperplastic polyps; large, medium, and small adenomas; and large and medium-sized hyperplastic polyps.[21]

Double-balloon enteroscopy

The small bowel has previously been one of the most endoscopically inaccessible areas of the gastrointestinal (GI) tract, with access limited by the distance achievable by using an enteroscope. Most diagnosis and treatment of lesions within the small bowel required open surgery.

Double-balloon enteroscopy, a method developed by Yamamoto et al, not only enables exploration of the entire small bowel but also allows for interventional therapy, including biopsies, hemostasis, polypectomy, and tattooing.[22] The double-balloon enteroscope has two balloons, one at the tip of the endoscope and the other on a transparent tube passing over the endoscope. Sequential inflation and deflation of these balloons as the endoscope is advanced allows for pleating of the bowel over the scope and forward movement through the small intestine. It can be used from either an oral (upper endoscopy) insertion or an anal (colonoscopy) insertion.


Colonoscopy is generally a safe procedure, and complications are rare. Such complications may include the following:

  • Colonic perforation [8]
  • Bleeding
  • Infection
  • Abdominal distention
  • Postpolypectomy coagulation syndrome
  • Splenic rupture
  • Small-bowel obstruction
  • Medication effects

Colonic perforation

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 in patients who are oversedated or under general anesthesia; in the presence of poor bowel preparation; and with acute bleeding. Generally, perforation 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 distention 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 distention or pain should prompt radiography, which 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 it is 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.

Immediate or delayed bleeding

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 for 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. Endoscopic hemostatic clips may also be used. Delayed bleeding usually stops spontaneously, though transfusions, endoscopic therapy, angiography, and even laparotomy may be required in more severe cases.

Transmission of infection

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 HIV have been made.

There have been a few cases reported of probable transmission of hepatitis C during colonoscopy. This was likely a result of inadequate cleaning and sterilization of the endoscope between procedures. Overall, the risk of transmission of hepatitis C during endoscopy remains small. 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.

Abdominal distention

Colonic distention during colonoscopy can cause notable discomfort and may also impair mucosal blood flow. Insufflation of carbon dioxide rather than air during colonoscopy may offer some advantages: carbon dioxide 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.

Splenic rupture

Splenic rupture during colonoscopy is a very uncommon complication; its presumed mechanisms 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 can be used for further evaluation.

Small-bowel obstruction

Small bowel obstruction is another rare complication of colonoscopy, though 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 distention 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.

Medication effects

Sedatives used during colonoscopy may cause complications from allergic reactions or, more important, 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. Administering these drugs with proper technique and sequencing, together with continuous monitoring of the sedated patient, can help minimize complications.