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Virtual Colonoscopy

 

 

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In Singapore, colorectal cancer is the commonest cancer in both men and women combined*. However, it can be cured if detected at an early stage and even prevented if the precancerous colonic polyp can be identified and removed.

However, health officials estimate that 80 to 85 percent of people avoid screening, partly due to the discomfort of conventional colon screening examinations – the barium enema and optical colonoscopy. Unlike optical colonoscopy, virtual colonoscopy requires no sedation because it is a minimally invasive procedure.

About Virtual Colonoscopy
Virtual Colonoscopy (VC) is also known as CT colonography and is a procedure that makes use of computed tomography (CT) to examine the colon and rectum for the presence of cancer or pre-cancerous polyps.

VC offers a relatively non-invasive, patient friendly investigation whereby, a small thin flexible tube is inserted into the rectum and air is used to distend the bowel. The patient then undergoes a CT scan, lasting only a few seconds. A radiologist with the aid of specialized computer software then analyzes the images.

Virtual colonoscopy has a high sensitivity for the detection of polyps as small as 1 cm in size (90-100% sensitivity)**. The test is less sensitive for polyps smaller than 0.6 cm in size, but the likelihood of such polyps being cancerous is low (<1%). While conventional optical colonoscopy can take over an hour or more to perform, virtual colonoscopy can be completed in 15-20 minutes and is does not require sedation. However, polyps detected with VC cannot be removed and conventional colonoscopy may still be required to remove any polyps if found.

In 2008, the American Cancer Society (ACS), American Gastroenterological Association (AGA), American College of Radiology and Radiological Society of North America endorsed VC as a first line option in screening for colorectal cancer. Cancer screening guidelines published in 2010 by the Ministry of Health, Singapore, now include VC as one of the screening options.

*Data from Singapore Cancer Registry, 2001-2005.
**Pickhardt PJ et. al. New England Journal of Medicine 2003; Volume 349:2191-2200.

Indications of Virtual Colonoscopy

Screening for colorectal cancer and polyps.

To image the entire colon when optical colonoscopy has failed to do so due to technical failure or an obstructing lesion.

When optical colonoscopy is contraindicated.

As with conventional colonoscopy, you must follow a bowel-emptying regimen the day before the examination to enable a clear view of the colon. You will be placed on a low residue liquid diet and prescribed laxatives to eliminate all solid material from your colon.

Further preparations are described in an instruction sheet given to patients.

The test requires rectal insertion of a narrow, flexible tube, through which air is pumped to expand the folds of the colon. You will lie both on your front and on your back on a padded table that will move through the scanner. You will be asked to hold your breath for up to 10 seconds.

An injection of intravenous contrast (dye) is not usually given for screening examinations. It is sometimes given when there is a need to exclude problems in other organs in the abdomen and pelvis as part of the exam. An injection to prevent spasm of the bowel may also be given.

Side effects and complications
Patients may experience some intestinal gas and a cramping sensation when air is pumped into the colon. Perforation of the bowel can occur but is very rare, occurring in less than 0.01%*** (compared with 0.1-0.13% for optical colonoscopy).

***Pickhardt PJ et. al. Radiology 2006; 239:313-316.

A normal diet may be resumed after the scan. The results of the scan will be sent to your doctor who may make further recommendations.