Colonoscopy and sigmoidoscopy
Colonoscopy and sigmoidoscopy are medical procedures used to examine the lower gastrointestinal tract. A colonoscopy involves the inspection of the entire large intestine, while a sigmoidoscopy focuses on the sigmoid colon, the section closest to the rectum. Sigmoidoscopy is typically quicker and can often be performed without sedation, although colonoscopy is generally preferred for comprehensive assessments, particularly for colon cancer screening. Both procedures require bowel preparation to ensure clear visibility during examination, which usually involves a clear liquid diet and a purgative the day before.
These procedures can also be used to investigate symptoms like blood in the stool, chronic diarrhea, and abdominal pain. Findings may include polyps, diverticula, or specific tissue changes indicative of certain diseases. Though mostly safe, there are risks associated with colonoscopy, such as perforation or bleeding, which are rare but can be serious. Patients are monitored post-procedure, especially if sedation was used. Overall, colonoscopy and sigmoidoscopy play crucial roles in gastrointestinal health and early detection of conditions like cancer.
Colonoscopy and sigmoidoscopy
Anatomy or system affected: Gastrointestinal system, intestines
Definition: The insertion of a flexible tube into the rectum to look at the inside surface of the colon
Indications and Procedures
Colonoscopy and sigmoidoscopy are common procedures to evaluate the lower part of the gastrointestinal tract. Colonoscopy refers to examination of the entire large bowel, whereas sigmoidoscopy examines only the part closest to the rectum (known as the sigmoid colon). The advantage of sigmoidoscopy is that it is less time-consuming and can be performed without sedation. Since sigmoidoscopy evaluates only part of the colon; however, full colonoscopy is often preferred. The most common reason for having a colonoscopy is to screen for colon cancer. If sigmoidoscopy is used for this purpose, it must be combined with a barium enema and an X-ray to evaluate the upper part of the colon.
Prior to colonoscopy, the bowel must be cleaned of stool to enable the physician to see the underlying mucosa. Patients are often asked to go on a diet of clear liquids (such as chicken broth, gelatin, and juice) for one to three days prior to the procedure. The night before the procedure, patients ingest a purgative to clear out any residual stool. The two most common preparations are polyethylene glycol (GoLytely) and a sodium phosphate mix (Fleet Phospho-Soda). Following ingestion of these solutions, patients should have clear or very light-colored liquid bowel movements. Regular medications that may cause excessive bleeding from biopsy sites, such as aspirin, warfarin, and nonsteroidal anti-inflammatory drugs (NSAIDs), are often discontinued prior to the procedure. Patients should also discontinue iron supplements, since they may create a black coating that makes it difficult for the physician to see the mucosa.
When patients enter the colonoscopy suite, they are given an intravenous (IV) catheter to administer fluids, as well as sedative and analgesic medications. Patients are asked not to eat or drink anything on the day of the procedure. Sedative medications sometimes cause nausea, and any food that is present in the stomach may be vomited. Blood pressure, pulse, and oxygen saturation are monitored throughout the procedure. The patient is positioned on his or her left side, and a colonoscope is inserted through the rectum into the colon. The colonoscope is a long, flexible tube with a fiber-optic channel connected to a camera. The image of the inside of the colon is transmitted to a television screen. The colonoscope also has channels to administer air or water, as well as a suction channel. Air is introduced to expand the walls of the colon, enabling better viewing. Water is used to remove residual stool that may obstruct the view of the colon. The colonoscope is advanced to the cecum (the first part of the large bowel) or even the terminal ileum (the last part of the small bowel). The instrument is then slowly withdrawn while any abnormalities in the mucosa are noted. Following the procedure, patients are often observed for a period of time to make sure that no complications occur. If sedative medications were used, patients should not drive or operate machinery for the rest of the day.
Uses and Complications
In addition to screening for colon cancer, colonoscopy and sigmoidoscopy can be used to evaluate blood in the stool, chronic diarrhea or other changes in bowel habits, and unexplained abdominal pain. Common findings include polyps, which may be biopsied. It is common practice to remove a polyp completely, in case it turns out to be the precancerous type (known as an adenomatous polyp). Other findings include diverticula, small outpouchings of the colon, which have very thin walls and are prone to spontaneous bleeding. They may also become infected, resulting in a condition known as diverticulitis. Other findings during colonoscopy may be useful in establishing the presence of a particular disease. Yellowish pseudo-membranes line the gut in colitis associated with the bacterium Clostridium difficile. A dusky hue is often seen in cases of ischemic colitis caused by diminished blood supply to the colon. Characteristic findings are also seen in inflammatory bowel disease.
Colonoscopy is a very safe procedure. One common aftereffect is abdominal discomfort as a result of the air used to distend the colon. This condition usually resolves over a few hours as the air is passed. The most serious complications of colonoscopy are perforation and bleeding. Perforation refers to a hole in the colon. It is an extremely rare occurrence, but it can be deadly. Patients with perforations often have severe abdominal pain and a rigid abdomen. If it is large and results in free air in the abdomen, a perforation requires emergency surgery. Rarely, very small perforations can be treated with observation and antibiotics. Bleeding is a risk if a biopsy is taken during the procedure. Most of the time, the bleeding stops by itself, but in some cases, a repeat colonoscopy may be required to control the bleeding. Rarely, bleeding may occur a few hours to several days after colonoscopy, so patients should report these symptoms to their physician. Whenever sedation is used, there is a risk of too much being given, which can lead to respiratory or cardiac arrest. Other possible complications include pain and inflammation at the site of the catheter and allergic reactions to sedative or analgesic medications.
Bibliography
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"Colonoscopy." MedlinePlus, 5 Dec. 2022, medlineplus.gov/colonoscopy.html. Accessed 20 July 2023.
"How to Prepare for a Colonoscopy." WebMD, 25 Mar. 2023, www.webmd.com/colorectal-cancer/prepare-for-colonoscopy. Accessed 20 July 2023.
Longstreth, George F. "Sigmoidoscopy." MedlinePlus, medlineplus.gov/ency/article/003885.htm. Accessed 20 July 2023.
Waye, Jerome D., Douglas K. Rex, and Christopher B. Williams, eds. Colonoscopy: Principles and Practice. 2nd ed., Blackwell, 2009.