Extracolonic Findings

Computed tomography colonography (CTC), also referred to as virtual colonoscopy, is a noninvasive CT examination of the colon that has shown promise as a tool for colorectal cancer screening. In most cases, CTC is performed without i.v. contrast at a reduced radiation dose. Therefore, in addition to intraluminal images of the colon, a noncontrast CT of the entire abdomen and pelvis, and often the lower thorax, is obtained. This allows CTC to image many organs other than the colon during a routine study, unlike other colon screening examinations such as endoscopy or barium enema. This ability can be seen as a double-edged sword (Hara 2005). In fact, the ability to evaluate extracolonic structures can present a clinical dilemma. On the one hand, CTC may incidentally demonstrate asymptomatic malignant diseases or other clinically important conditions, thus possibly decreasing morbidity or mortality. On the other hand, CTC may reveal numerous find-ings of no clinical relevance. This could result in costly additional diagnostic examinations with an increase in morbidity and an overall negative effect on a patient's health (Sosna et al. 2005). Only a minority of the extracolonic findings observed by means of CTC are clinically important (Zalis et al. 2005; Pickhardt et al. 2003; Hara et al. 2000). Excessive caution and ambiguity in the description of findings, which are almost certainly benign, can lead to considerable follow-up examination costs and unnecessary anxiety for the patient (Zalis et al. 2005). But there are also technical considerations to put forth. In fact, it is also important for the interpreting radiologist to remain cognizant of the diagnostic limitations imposed by the reduced X-ray dose and infrequent use of intravenous contrast material that are typical when screening colorectal cancer via CTC.