Virtual colonoscopy has gained the potential of being a diagnostic modality which may be tolerated better by patients and considered noninvasive by its rapid development in the recent years. Although it is not used routinely in the detection of colonic polyps and cancer today, the ongoing developments in the visualization and computerized systems allow CT to play an important role in detection of polyps and early-stage colon cancer [29]. However, when the current literature is checked, it can be seen that virtual colonoscopy is suggested to be used for a limited indication as a diagnostic tool in cases that optical colonoscopy could not completed (because of problems such as relative sensitivity, technical limitations, lack of standardization) [30].

In CT colonography, the patient’s bowel must be cleaned as in conventional colonoscopy. Hyoscine butylbromide (Buscopan®) or glucagon injection is needed in order to prevent peristaltism during the examination. The lesions in the lumen are evaluated by giving enough air to distend the bowels. Carbon dioxide or room air can be used for colonic distension. It is proposed that using carbon dioxide will cause a less painful distension than using room air. The use of smooth muscle relaxants is controversial, and it is not preferred because it may cause agitation [31].

Using volumetric data obtained from the patient in the prone and supine positions, multiplanar reconstructions and three-dimensional endoluminal column images are obtained by special computer softwares after CT examination (current spiral CT technology allows abdomen to be scanned in a period as short as 20 s) (Fig. 12.3). Getting the image sections of the patient in the prone and supine positions naturally increases the radiation dose received by the patient. However, it is necessary to evaluate the 3D sections taken in both positions along with the 2D sections for the differentiation of the residual liquid and fecal remnant in the colon lumen from polyps (Fig. 12.4). Getting sections in one position and examination with a low dose radiation in order to reduce the dose of radiation reduces the sensitivity of virtual colonoscopy [32, 33].

In large series conducted in recent years, the place of CT and MR colonoscopy has been being analyzed. In the literature there are a wide range of publications (55–100 %) on the sensitivity of virtual colonoscopy that may be contradictory.

In a comparative study on CT virtual colonoscopy and conventional colonoscopy performed by Fenlon et al. in 1999, 115 polyps and 3 cancers were detected in a high-risk group for colorectal cancer of a total case of 100 (60 men, 40 women). Both CT and conventional colonoscopy detected all three cancer cases. In 49 cases pathologically detected, while the effectiveness in the lesions smaller than 5 mm was 55 % for CT colonoscopy, it was found in 67 % for conventional colonoscopy. However, CT and conventional colonoscopy results in 6 mm and larger lesions were found to be close to each other (82 and 90 %) [15]. While Macari found the sensitivity of CT colonography as 11.5 % for polyps smaller than 5 mm in his study in 2004, Chunk reported the sensitivity as 84 % in 2005 [34, 35]. They reported the sensitivity of CT and conventional colonoscopy for polyps between 6 and 9 mm as 52.9 % and 94 %, respectively. In both studies, the sensitivity for polyps larger than 10 mm is 100 % [36].

In the study by Luboldt et al., published in August 2000, the conventional and MR colonoscopy results of 127 cases with predetermined mass in the colon were compared. Most of the lesions of 5 mm and smaller could not be detected by MR. MR was found effective in 67 % of the lesions between 6 and 9 mm and in 96 % of the lesions larger than 10 mm. For MR colonoscopy, 93 % sensitivity; 99 % specificity; 52 % positive predictive value; and 98 % negative predictive value were found for lesions larger than 10 mm [37].

In a series of 29 cases with occluding cancers, 2 synchronous cancers and 24 polyps were detected in the proximal colon by virtual colonoscopy. Two cancer cases were confirmed at surgery. In the postoperative colonoscopy performed for 12 cases, the presence of polyps that were detected with virtual colonoscopy were confirmed and two more polyps were found that had not been detected before [38].

Advantages and disadvantages of virtual colonoscopy compared to colonoscopy can be summarized as follows:

The purpose in virtual colonoscopy is to detect polyps of 10 mm and larger ones. Cancer rate is 1–5 %; adenoma rate is 80 % in polyps of 10–15 mm. The incidence of cancer for the adenomas detected within 10 years is 10–15 %, and generally the incidence of cancer for polyps of 10–15 mm within 10 years is 10–15 %. The risk of malignancy in polyps smaller than 5 mm is less than 0.1 % [39].

Despite all this information, even though the size of the lesions detected in virtual colonoscopy is larger than 10 mm, colonoscopy is needed for confirmation and treatment in practice [38].

Naturally, colonoscopic polypectomy is effective and a minimally invasive method and it prevents progression and is a precise curative technique in polyps that have not progressed up to submucosa but show malignant transformation [40].