Colonoscopy Technique

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

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.