Screening Colonoscopy
MD Anderson Cancer Center 2011

Hello. Part of MD Anderson's mission is to eliminate cancer by providing prevention and early detection programs. One of these programs screens for colon cancer which is the third most common cancer in the United States. When detected early, there is nearly a 90 percent chance for a cure of colon cancer. However, there are often no symptoms in its early stages. It is recommended that men and women at average risk for colon cancer begin screening at age 50. Fortunately, several screening exams are available to find colon cancer early when it is easiest to treat and has the greatest chance for cure.

MD Anderson recommends optical colonoscopy or virtual colonoscopy because both of these exams screen for and prevent colon cancer. Optical colonoscopy uses a flexible tube with a tiny camera which allows the doctor to view the inside of the colon. Virtual colonoscopy uses computerized tomography, CT scanning and 3D computer technology to make images of the inside of the colon.

Both exams require you to cleanse your bowels and get rid of stool. This helps your doctor see your colon clearly. It involves limiting your diet to clear liquids, drinking a special cleansing solution and taking oral laxatives.


 The most widely used diagnostic exam is optical colonoscopy. During this procedure, the doctor inserts a long flexible lighted tube into your colon to look for precancerous lesions called polyps. The tube is about as wide as a finger. It is inserted through the anus and is gently guided to the other end of the colon. The tube has a tiny video camera on the end, so your doctor can see the inside of your colon to look for polyps. You will be given medicine to help you relax and sleep during the exam and you will feel little to no discomfort.


The scope takes the shape of the colon very easy without causing any stretching or pain. So, when a patient is undergoing a procedure, for example, a full colonoscopy, there should not be any pain.


If a polyp is found during the optical colonoscopy, the doctor will remove it at that time. A small instrument is passed up through the colonoscope to remove the polyp. The polyp is then sent to the pathologist who looks at it under a microscope to see if it contains cancer. If no polyps are found, the exam usually lasts about 30 minutes. You will then stay in recovery for 30 minutes while the effects of the sedation wear off. A responsible adult must come with you to the appointment to drive you home.

The greatest advantage of optical colonoscopy is that the doctor can find and remove polyps immediately. Removing polyps is the best way to prevent colorectal cancer.

There are also several disadvantages of optical colonoscopy, most notably, sedation is used. This means a responsible adult must come with you to the appointment. There is also a risk of complications from using the sedative. Also there is a small risk of tearing of the colon from the insertion of the tube.



Virtual colonoscopy uses CT scanning and 3D computer technology to create pictures of the colon and to find any polyps that might be there. A CT scanner is a type of x-ray machine that can look inside the human body. To see your colon clearly during CT scanning, an iodine containing solution and carbon dioxide gas are given through a small tube inserted about 4-inches into the colon. The solution and gas fill and expand your colon so it is easier to see. The CT scanner then takes images of the colon which are used by a computer to create 3D images.

No sedation is used during virtual colonoscopy so you will be awake and able to talk the entire time. You may feel some discomfort such as bloating as the gas fills your colon. The exam usually lasts about 10 to 20 minutes. Since you are not sedated, there is no recovery time.

You will have an appointment with the healthcare provider several hours after the exam to go over the results. If polyps are found, you will need to have an optical colonoscopy to remove the polyps. The optical colonoscopy may be done on the same day or at a later time. It is recommended that you continue to not eat or drink until you find out whether an optical colonoscopy is needed.

An advantage of the virtual colonoscopy is that it can spare many people from having to undergo the more invasive optical colonoscopy.

So, the goal of doing virtual colonoscopy is to eliminate unnecessary colonoscopy in those patients that have a normal colon. Only about 10 percent of the population has a polyp that needs colonoscopy for polyp removal. So, what we hope to do is eliminate unnecessary colonoscopy in about 90 percent of the population with this virtual technique for screening.


Another advantage of virtual colonoscopy is that sedation is not used, so you can return to your normal activities after the exam.

There are also several disadvantages of virtual colonoscopy. Most notably, polyps cannot be removed during a virtual colonoscopy. If a polyp is found, an optical colonoscopy must be performed to remove the polyp. You are exposed to a very low dose of radiation, there is a small risk of an allergic reaction to the iodine containing solution, and there is a small risk of tearing of the colon from the insertion of the tube.


If you have any questions about optical or virtual colonoscopy, talk with your healthcare provider. Together, you can decide what the best colorectal cancer screening test is for you.