Current Status of Virtual Colonoscopy

Current Status of Virtual Colonoscopy

Hassan Cesare , Laghi Andrea
European Gastroenterology & Hepatology Review - Volume 4 - Issue I
Published: January 2009
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2008 will be remembered as the beginning of a new era for virtual colonoscopy (VC), also known as computed tomography colonography (CTC). In fact, it was on 5 March 2008 that the major scientific societies – including the American Cancer Society (ACS), the American Gastroenterological Association (AGA) and the US Multi-Society Task Force on Colorectal Cancer – released the new guidelines for colorectal cancer (CRC) screening, which for the first time included VC among the optional available tests.1 This is the result of a long process that began in 1994, when VC was proposed by Vining and Gelfand,2 and is still ongoing, since the results of major multicentre trials have been presented at meetings but are still going through the peer-review process.

What Is Virtual Colonoscopy?
VC is a minimally invasive imaging modality for the evaluation of the colon based on volumetric, thin-collimation CT acquisition of a cleansed and air-distended colon; CT data sets are edited off-line in order to produce multiplanar reconstructions (coronal and sagittal images) and 3D modelling, including endoscopic-like views (see Figure 1). The major difference compared with optical colonoscopy is that on VC an image of the entire wall is obtained, including the internal surface (the mucosa) as well as the outer layers; extracolonic findings residing in the surrounding abdomen and pelvis can be analysed as well. On the other hand, the major limitations of VC compared with optical colonoscopy are the ‘unreal’ colour of the mucosal surface (preventing the identification of abnormal mucosal pigmentation, i.e. melanosis coli) and the impossibility of mucosal or lesion biopsy.

What About the Technique?
The technique is extremely easy and it is less labour-intensive than barium enema and conventional colonoscopy. It consists of four consecutive steps: bowel cleansing, patient preparation, scanning protocols and image analysis.

Bowel Cleansing
As in conventional colonoscopy, bowel cleansing is critical in VC, and an optimal examination requires a clean colon. In fact, the presence of stool may mimic an endoluminal lesion and faeces may hide the presence of either a polyp or a colonic carcinoma. The ideal colonic preparation is still under debate. It is the general consensus that patients should undergo a low-residue diet for two to three days before the examination, and should ingest a cathartic agent (polyethylene glycol electrolyte solution, phospho-soda, magnesium citrate) the day before.3 A low-volume preparation (i.e. phospho-soda or magnesium citrate) might be preferred because of the lower amount of residual fluids, negatively affecting the evaluation of colonic mucosa (the colon is ‘drier’).4

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