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Examination of the colon

Most of the gastrointestinal (G.I.) tract from the esophagus to the anus can be examined by endoscopy (endo, inside; scope, see; to see inside the body). The endoscope is a long and flexible tube and contains a light source, lens system for focusing and fiber optics to conduct light into the bowel. A picture of the bowel wall is sent back to a video camera and displayed on a monitor. The tube also contains a working channel through which small instruments can be passed for various uses. Colonoscopy enables the physician to examine the lining of the colon (large bowel), and is done by inserting the flexible endoscope (called a colonoscope) into the rectum and then into the entire colon.

Anatomy and Physiology

The large bowel absorbs 90% of the water content of the digested food it receives from the small intestine. It also propels the residue towards the rectum, where it is stored and expelled with a bowel movement. The large bowel is composed of:

  • Colon. The colon averages 150 cms. (60 inches) in length. The colon is divided into four segments: the ascending colon, transverse colon, descending colon and sigmoid colon. There are two bends (flexures) in the colon. The hepatic flexure is where the ascending colon joins the transverse colon. The splenic flexure is where the transverse colon merges into the descending colon. (Figure 1)
    1. Cecum. This is the first portion of the large bowel and is joined to the small bowel at the ileocecal valve. (Figure 2) The appendix lies at the lowest portion of the cecum. (See Colectomy and Appendectomy)
    2. The ascending colon is about eight inches in length, extends upwards from the cecum to the hepatic flexure near the liver
    3. The transverse colon is usually over 18 inches in length and extends across the upper abdomen to the splenic flexure
    4. The descending colon, usually less than 12 inches long extends from the splenic flexure downwards to the start of the sigmoid colon
    5. The sigmoid colon is S-shaped and measures about 18 inches long. It extends from the descending colon to the rectum
  • Rectum. The rectum is a curved pouch that lies in the hollow formed by the sacrum and connects with the anal canal at its lower end
  • Normal colon wall is seen in Figure 3
Figure 1 - Anatomy of the colon from the junction with the ileum to the rectum.
Figure 2 - View of the ileocecal valve as seen from the cecum. Courtesy M. Takriti, MD Figure 3 - Normal colon wall as seen on colonoscopy. Courtesy M. Takriti, MD


  • Cancer of the colon and rectum is common in patients over age 50 and steadily rises thereafter. (Figure 4) Americans have about a five percent chance of developing colorectal cancer if they live to 70 years of age
  • Polyps are thought to progress to cancer (Figure 5A)
  • Diverticulosis is a condition that is common in western society. It increases with age and is present in approximately 75% of Americans over the age of 80. It is associated with diverticula, which are protrusions of the innermost lining of the colon through the muscular outer layers of the colon wall. The diverticula can become inflamed, a condition called diverticulitis, which can cause perforation of the bowel with abscess, bleeding, obstruction of the bowel or fistulae of the colon (a communicating hole between the colon and other organs such as the small bowel, urinary bladder, vagina or skin) (Figure 6)
  • There may also be inflammatory bowel disease namely Crohn's disease, ulcerative colitis and ischemic (decreased blood supply) colitis. These conditions result in inflammation of the colon that can involve the entire thickness of the colon wall (Crohn's disease, ischemic colitis) or only the mucosa, the innermost lining of the colon (ulcerative colitis, Figure 7)
Figure 4 - Cancer of the colon. Courtesy M. Takriti, MD


  • Indications for colonoscopy are:
  • Blood in the stool
  • Preventive colonoscopy. Periodic colonoscopy is desirable over the age of 50 to detect polyps
  • Polyp found on X-ray studies
  • Persistent diarrhea or constipation
  • Imaging studies (barium enema, CT scan, MRI) suggestive of an abnormality


  • The colon must be completely cleaned for the procedure to be accurate and complete. In general, preparation consists of being on a liquid diet the day before the test and taking of laxatives to clean the bowel (Figure 9)
  • Most medications may be continued as usual but some medications may interfere with the preparation or examination. Therefore, the physician should be told of the medications that the patient is taking as well as any allergies to medications. Aspirin products, arthritis medications, anticoagulants (blood thinners, i.e. Coumadin, Plavix), insulin and iodine products are examples of such medications. The patient should also alert the physician if he requires antibiotics prior to the procedures
  • Colonoscopy is usually done under sedation. It is common for patients to sleep during the procedure. Some discomfort, such as a feeling of pressure, bloating or cramping, or pain may be encountered at times
  • The patient lies on the left side or sometimes on the back during the procedure
  • The colonoscope is slowly inserted into the rectum and slowly advanced through the colon while the physician removes any residual material missed by the preparation and observes the wall of the bowel. As the colonoscope is slowly withdrawn, the lining is again carefully examined. In some cases, passage of the colonoscope through the entire colon to its junction with the small intestine cannot be achieved
  • The procedure takes between 15-30 minutes. If the examination is not complete, the physician will decide if other examinations are necessary
  • If an area of the bowel wall needs to be evaluated in greater detail, a forceps instrument is passed through the colonoscope to obtain a biopsy. The specimen is submitted to the pathology laboratory for analysis
  • If sites of bleeding or a potential bleeding site is found, the bleeding may be controlled by injecting certain medications or by coagulation with electricity, heat or laser
  • Polyps are removed (Figure 5B)
Figure 5a - Polyp of the colon before removal. Courtesy M. Takriti, MD Figure 5b - Colon after removal of polyp seen in A. Courtesy M. Takriti, MD
Figure 6 - Bleeding diverticula (arrows) as seen on colonoscopy. Courtesy M. Takriti, MD Figure 7 - Example of ulcerative colitis. Courtesy M. Takriti, MD


    1. Polyps are an abnormal growth from the lining of the colon which vary in size from 2-3 mm. to several centimeters
    2. The majority of the polyps are benign (non-cancerous), but the examining physician cannot always tell a benign from a malignant (cancerous) polyp by its appearance alone. For this reason, removed polyps are sent for tissue analysis. Most colon polyps are completely removed
    3. Removal of the colon polyps is an important means of preventing colon cancer
    4. Tiny polyps may be totally destroyed by fulguration (burning), but larger polyps are removed by technique called snare polypectomy. The doctor passes a wire loop (snare) through the colonoscope and severs the attachment of the polyp from the intestinal wall by means of an electrical current
    5. There is a small risk that removing a polyp will cause bleeding or result in a burn to the wall of the colon, which could require emergency surgery (Figure 9A,9B)
Figure 8 - Various endoscopes for examination of the colon and rectum. Each endoscope is positioned opposite the point in the colon to which that scope can reach. Only the colonoscope can reach the ileum.
Figure 9a - Jet of blood following removal of a polyp. Courtesy M. Takriti, MDFigure 9b - Bleeding stopped by cauterizing the vessel (arrow). Courtesy M. Takriti, MD
  • Following the procedure the colonoscope is removed


  • Perforation or tear through the bowel wall that may require surgery
  • Bleeding may occur from the site of biopsy or polypectomy. It is usually minor and stops on its own or can be controlled through the colonoscope. Rarely blood transfusions or surgery may be required
  • Other potential risks include:
    1. Reaction to the sedatives
    2. Complication from associated heart or lung disease
    3. Localized irritation of the vein where medication was injected. Applying hot packs or hot moist towels may relieve discomfort
  • Although complications after colonoscopy are uncommon, it is important for the patient to recognize early signs of any possible complication. The patient should contact the physician if any of the following symptoms are being observed:
    1. Severe abdominal pain
    2. Fever or chills
    3. Rectal bleeding of more than one-half cup. Bleeding can occur several days after polyp removal

After Care

  • After the test, patients are monitored in the recovery area for 30 - 45 minutes, until the effects of sedation have worn off. They will need to make arrangements for somebody to drive them home (not a taxi) and to stay with them for the remainder of the day because the sedation affects judgment and reflexes for the rest of the day. No driving or working is allowed until the next day. It is advised to have somebody stay with the patient for the rest of the day
  • There may be some cramping or bloating because of the air introduced into the colon during the examination. This disappears with the passage of flatus (gas)
  • Generally the patient should be able to eat after the endoscopy, but the physician may restrict the diet or activities, especially, after extensive endoscopic work (i.e. large polypectomy, control of bleeding, etc).
  • The doctor will discuss with the patient or designated companion any further instructions or need for follow up