Definition and Overview
Colonoscopy is a commonly used diagnostic test that enables doctors to visually inspect the large bowel. It provides very clear images of the intestines through a video camera attached to one end of the scope (colonoscope), which is passed through the patient’s large bowels. It is most commonly used to check for colorectal cancer, purely for diagnostic purposes. However, it can also be used to remove lesions as a form of treatment.
Who Should Undergo and Expected Results
Lesion removal colonoscopy is highly recommended for patients who are suspected of having colon polyps, or abnormal growths in the colon. Patients with colon polyps may experience any of the following symptoms:
Abnormal or sudden changes in bowel habits
Rectal bleeding or bloody stools
This test is also recommended for those who are at risk of colon cancer. These include:
Men and women over the age of 50 – These patients are considered to have an average risk of developing colorectal cancer and are advised to undergo colonoscopy every 10 years
Patients with colorectal polyps - Even if what they have are small hyperplastic polyps, they are still considered to be at high risk, and should therefore undergo the procedure immediately followed by a more intensive follow-up care plan
Patients who have first-degree relatives with colon cancer – Patients who fall under this category should start undergoing colonoscopies at age 35-40
Studies show that only 5% of patients who have colorectal polyps develop colorectal cancer. This means that the majority of bowel polyps are not malignant. Nevertheless, their removal via colonoscopy still contributes to the prevention of colon cancer. In fact, colonoscopy in general is considered as one of the most effective cancer prevention methods. Studies show that up to 60% of colon cancer deaths could be prevented if everyone over the age of 50 regularly undergoes colonoscopies.
There are many different types of lesions or polyps that can grow in the colon. These include:
Adenomatous polyp – These are common, gland-like growths that form on the mucous membrane, or the lining of the large intestine. They are also called adenomas or tubular polyps. These polyps have a high chance of becoming cancerous, in which case they become known as adenocarcinomas, the most common type of colon cancer.
Flat polyp – These are considered as some of the most dangerous types of lesions, particularly due to their flat appearance that makes them easy to miss or overlook during a colon cancer screening. They are also likely to be more cancerous.
Hyperplastic polyp – This type of lesion does not commonly develop into cancer.
Serrated polyp – This is a less common type of colon lesion that has the potential to develop into cancer over time.
Sessile polyp – Sessile serrated polyps are also considered as flat polyps since they do not have a stalk. They usually grow on the inside wall of the colon and have a tendency to turn into cancer. Fortunately, sessile polyps can be removed during a colonoscopy.
Patients who have polyps removed via colonoscopy should continue having diagnostic colonoscopies. The time between tests depends on the size or severity of their previous lesions. Patients with 1 or 2 small lesions should undergo a colonoscopy every 5 to 10 years, whereas patients with 3 or more larger lesions found on a single exam should undergo the procedure every 3 years. Lastly, patients with sessile polyps should undergo colonoscopy 2 to 6 months after the polyps are removed.
How is the Procedure Performed?
Colonoscopy, whether performed for diagnostic or therapeutic purposes, is a minimally invasive, relatively painless procedure. It involves inserting a flexible scope into the patient’s large intestines. This instrument, called colonoscope, is specially designed to evaluate the entire large intestine (around 3 to 4 feet in length). It is also designed so that other procedures can be performed while it is in the colon. These include biopsies and lesion removal.
The colonoscope works by taking a video of the colon and transmitting it to a computer screen. If a polyp or lesion is found, the doctor will determine if it is possible to remove it during the same procedure. The patient is placed under intravenous sedation throughout the whole procedure, which means that they are drowsy but very comfortable and able to breathe on their own.
Prior to undergoing colonoscopy, there are some preparatory steps involved. Patients are advised to undergo a colon cleansing procedure, which will make the visual examination more effective. Most doctors recommend drinking polyethylene glycol (PEG), which causes the patient to experience diarrhea to effectively remove the contents of the colon. 50% of the solution is taken in the late afternoon or evening on the day prior to the test, while the other half is taken around 5 hours before the test.
Patients are also asked to consume clear liquids the day before the test up until 2 hours before it. On the night before the test, some patients are also advised to take laxatives.
Aside from PEG, patients can also take a phosphate solution or phosphate tablet, which are very effective in cleansing the colon.
Possible Risks and Complications
While very effective, colonoscopies do have some disadvantages. Colonoscopies tend to be more effective at detecting cancer in the left side of the colon than in the right. This may be due to the fact that the right side of the colon is more prone to flat and pale lesions that are difficult to detect, and even when detected, difficult to remove through colonoscopy.
The accuracy of a colonoscopy is also affected by the experience level and skill of the doctor performing the procedure. For best results, the test should be done by a skilled gastroenterologist, and the patient should be adequately prepped for the procedure.
Colonoscopy is also not without potential complications, although the risk is small and relatively insignificant. These include colon perforation and bleeding.
There are also some complications related to the use of sedation and these may include some cardiac and respiratory issues. The risk, however, is quite low, especially when compared to the risk of developing colon cancer.
“American Cancer Society recommendations for colorectal cancer early detection.” American Cancer Society. https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/acs-recommendations.html
“Do you need a colonoscopy?” April 1, 2012. Berkeley Wellness, University of California. http://www.berkeleywellness.com/self-care/preventive-care/article/do-you-need-colonoscopy