One of the promising methods for the diagnosis of a tumor of the colon is a virtual colonoscopy – an approach based on spiral computed tomography with highly thin sections and three measurement diameters. The sensitivity of virtual colonoscopy is 93.8%, and the specificity is 96% for polyps with a diameter of> 10 mm (Lambert et al., 2015). The value of virtual colonoscopy as a diagnostic method is not in doubt, but its place in the preoperative examination and stage determination of colon cancer has not yet been conclusively determined. When analyzing the causes of false-positive and false-negative results, it was found that one of the advantages of virtual colonoscopy compared to optical imaging is the ability to identify the submucosal component of tumors.
Virtual colonoscopy is performed using a PQ 5000 helical computed tomography scanner with the following parameters: beam collimation 5 mm, tomograph table speed 6.25 mm / s, step 1.25, 110 mA, 110 kV (Hellström, 2014). Images for virtual colonoscopy are obtained 4-6 hours after flexible colonoscopy. The diagnostic procedure is performed after standard preparation of the intestine with additional parenteral administration of antispasmodics. Before scanning, the intestinal lumen is filled with a moderate amount of air, the extra amount of air necessary for full visualization of the intestinal lumen is introduced after the first tomograms are obtained.
Visualization of the lumen of the colon is carried out with the movement of the virtual camera in the forward and retrograde direction. The resulting images are compared with the relevant and adjusted colonoscopy data. The total duration of the procedure is, on average, 40 minutes, and the analysis of the data obtained, on average, takes 15 minutes (Lambert et al., 2015).
The protocol of virtual colonoscopy records the number, localization, and size of all detected neoplasms. Evaluation of the results of the work is carried out using the method of descriptive statistics. The mean value is determined, the error of the mean, standard deviation, amplitude, differences were considered significant at p <0.05.
Virtual colonoscopy shows itself as a highly informative method for examining the colon, especially for malignant tumors obstructing the lumen, when assessing the state of the intestine proximal to the neoplasm is impossible using other imaging methods. In such situations, optical colonoscopy is ruled out due to the impossibility of introducing a colonoscopy, and irrigoscopy data cannot be considered final due to the difficulties in adequately filling the intestinal lumen with barium suspension. Virtual colonoscopy, even in these conditions, allows obtaining additional data on the localization and prevalence of the malignant process, as well as polypus lesions.
At the same time, it is important to carry out a multi-position scan, which allows realizing the full diagnostic capabilities of virtual colonoscopy, which is especially important in the case of multicentric synchronous malignant growth (Hellström, 2014). Combined virtual and optical colonoscopy seems to be optimal at the stage of preoperative diagnosis since it makes it possible to obtain maximum information about the localization, prevalence, and nature of neoplastic lesions based on histological examination of biopsy specimens.
In conclusion, virtual colonoscopy is the method of choice for topical diagnosis of neoplasms of the colon, especially in the presence of subtotal obstruction of the lumen by the tumor. A virtual colonoscopy with mandatory scanning in various positions of the patient can be considered full-fledged. The optimal stage of the examination is a combination of optical and virtual colonoscopy methods.
Hellström, M. (2014). CT colonography: A guide for clinical practice. Acta Radiologica, 55(5), 543-544.
Lambert, L., Danes, J., Jahoda, J., Masek, M., Lisy, J., & Ourednicek, P. (2015). Submilisievert ultralow-dose CT colonography using iterative reconstruction technique: A feasibility study. Acta Radiologica, 56(5), 517-525.