Colorectal cancer is the third most common cancer and the second leading cause of cancer-related death in Western countries. As with other malignancies, screening and early detection is fundamental for successful management of colorectal cancer. Computed tomographic (CT) colonography is a noninvasive, rapidly evolving technique that has been shown in some studies to be comparable with conventional colonoscopy for the screening of colorectal cancer. CT colonography is being increasingly applied as a routine screening method for the detection of colorectal cancer in last few years as it is more convenient and less invasive than colonoscopy. In addition, it has an upper hand in diagnosis of small lesions less than 10mm  (Choi, et al., 2011).
Patients and methods:This prospective double blind comparative study will be conducted on 23 patients with colorectal symptoms and signs as altered bowel habits, bleeding per rectum, abdominal pain, weight loss, unexplained fatigue and loss of appetite.An informed written consent was obtained from all patients and approval of the faculty research ethics committee was obtained.
Results:  Total of 108 colonic lesions were analyzed in 23 patient; Seven colonic masses were diagnosed in 6 patients, 41 polyps in 8 patients and 60 diverticulae in 5 patients.
Six patients had incomplete colonoscopy. Of them, 2 patients had a large polypoidal mass that prevents further colonoscopic introduction. Using CT colonography we were able to evaluate those polypoidal masses. Moreover, we could complete the examination and evaluation of the proximal colon and one of them had a polypoidal sigmoid colon mass and showed another proximal annular mass.
Four patients presented with colonic obstruction and good preparation to the proximal parts of the colon failed, So completing the colonoscopy was difficult. After  undergoing CT colonography, 2 patients were normal and 2 patients had annular masses causing proximal obstruction and marked distension.
ConclusionCT Colonography (Virtual Colonoscopy) is a reliable tool and more sensitive for detecting colonic mass lesions larger than 5 mm, polyps larger than 5 mm, strictures and diverticulosis. CTC is of value in evaluating the colonic segment lying proximal to colonic cancers including those with occlusive growths or strictures. Contrast-enhanced CTC is also useful in identifying extra-colonic findings.Virtual Colonoscopy is a good screening tools for malignant or premalignant lesions in patients presented with colorectal symptoms.