Virtual colonoscopy: overview, indications, preparation, procedure and limitations

Colonoscopy is a procedure during which the inside of colon is visualized. Colon is a hollow tube-like part of our large intestine that absorbs mainly water from the digested food to convert them into feces. Traditional colonoscopy requires an endoscope known as colonoscope to be inserted into the colon. Virtual colonoscopy is a method in which colon is visualized without any insertion of an endoscope. That’s why it is called as virtual. It is also known as computerized tomography (CT) colonography. Virtual colonoscopy is used for the early detection of cancers of colon and rectum.

Virtual colonoscopy is different from colonoscopy in many ways. During a colonoscopy procedure, a long, narrow and flexible tube with a camera and light fitted on the tip is used to see the inside of the colon and rectum. The tube needs to be inserted through the anal opening and anesthesia is required but virtual colonoscopy doesn’t utilize this method and has the following advantages

• Less invasive: a scope or colonoscope is not required as it uses a CT scan which takes hundreds of images of the large intestine. These images are later combined with the help of software to produce a detailed view of the inside of the wall of colon and rectum
• No requirement of anesthesia
• Takes less time
• Does not require specialists to insert the scope as the scope is not used
• Since other organs like kidney, liver or pancreas also get visualized while taking pictures of the large intestine, potential abnormalities with these organs may also get detected.

Indications

Virtual colonoscopy is used for screening or early detection of polyps or cancers of colon and rectum. Colorectal cancers have become more common nowadays. Early detection of disease has higher chance of getting cured. Polyps are the outgrowth of the wall of the intestine into the lumen. Not all polyps are cancerous, they can be non-cancerous too but detection of polyps raises a suspicion. In healthy people who are not at being a risk of developing colon cancer, it is recommended that they get screened for colorectal cancer at the age of 50. Virtual colonoscopy can be also done when

Colonoscopy can’t be done due to some health issues of the patient like increased risk of bleeding that doesn’t clot.

Patients suffering from bowel obstruction

Screening is done at younger ages when the individual is at risk and colonoscopy is preferred in these individuals.

The risk factor which makes an individual more likely to have colorectal cancer are

• When the individual has a history of inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis.
• Family history of colorectal cancer or a history of polyps.
• Too much weight
• History of smoking
• Intake of low fiber diet

Preparation

Prior going for virtual colonoscopy, you need to prepare your body. Your doctor will ask questions about your current medical illness, medical history, past or current medications. Virtual colonoscopy can’t be performed in pregnancy. Implanted medical devices may interfere with the procedure such as a pacemaker.

You need to change your diet to clean out your bowel. It is called as bowel prep. To get a good visualization of the inner wall of the colon and rectum, the bowel should be stool free. Therefore, the patient is shifted from the solid diet to liquid one and the procedure is not started unless the patient is passing clear-liquid stools. The instructions about the clear liquid diet specifying the time duration and the content of the diet will be provided to you. Your liquid diet may consist of

• Plain tea or coffee without milk and cream
• Sports drinks
• Clear fruit juice
• Water

You will drink a contrast medium the night before the procedure. It will spread over the inner walls of the colon and rectum. It appears opaque on the x-rays, therefore, making the wall appear visible too. Any abnormality or irregularity in the wall structure will get visible.

Procedure

You will lie on a table with an overlying circular tunnel-like machine under the supervision of specially trained x-ray technician. A thin tube will be inserted through the anus to inflate the large intestine to provide better visualization. Anesthesia is not required for the insertion of this tube. You may be asked to hold your breath several times to obtain steady images. You will also need to turn to different positions to capture images at different angles.

The entire procedure lasts for around 10 to 15 minutes and the individuals can resume their daily activities after a few minutes.

Results

Radiologist will look at the images and would give comments. The report will be sent to your doctor as well. If any polyp or abnormality is detected, your doctor may suggest performing a colonoscopy to take the sample of the polyp. If abnormalities with other organs are suspected then your doctor may advise some additional tests.

Limitations

Virtual colonoscopy is a good method for screening but it has the following disadvantages over colonoscopy

• It is not as much effective in finding a certain type of polyps which are small in size.
• This method is not therapeutic that means, unlike colonoscopy it can’t be used to take the tissue samples from the polyps and remove them.

Complications

Side effects such as nausea, vomiting, abdominal cramps are associated with every bowel preparation. Inflating the large intestine with the help of gas can rarely perforate the bowel which need to be treated with surgery. If an individual experience severe abdominal pain, fever or weakness after undergoing virtual colonoscopy, he or she need to seek urgent medical attention.

References

• Levine MS, Yee J. History, evolution, and current status of radiologic imaging tests for colorectal cancer screening. Radiology 2014; 273:S160.
• Levin B, Lieberman DA, McFarland B, et al. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: a joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. Gastroenterology 2008; 134:1570.
• U.S. Preventive Services Task Force. Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2008; 149:627.
• Pickhardt PJ. Incidence of colonic perforation at CT colonography: review of existing data and implications for screening of asymptomatic adults. Radiology 2006; 239:313.
• Pendsé DA, Taylor SA. Complications of CT colonography: a review. Eur J Radiol 2013; 82:1159.