The public health need for colorectal cancer screening is compelling. Colorectal cancer is common, accounting for approximately 50,000 deaths yearly in the USA [1]. The benign precursor, adenoma, can be detected by several different imaging techniques and removal can prevent malignant transformation. The approximately 10-year polyp dwell time allows ample opportunity for patients to be screened and polyps detected and removed. Potentially, under ideal screening circumstances, an entire class of cancers could be prevented. However, barriers exist to ideal screening, including suboptimal performance of many existing colorectal screening tests, reluctant compliance by patients to follow recommended screening guidelines, and variable insurance coverage of examination charges. In many ways, computed tomography colonography (CTC) approaches an ideal screening test by addressing issues and problems inherent with other techniques. This syllabus highlights many key issues for CTC.

The performance of CTC has undergone exhaustive testing. The Department of Defense (DoD) trial conducted by Pickhardt et al. demonstrated sensitivity similar to colonoscopy [2]; however, concerns were raised that community practices might not be able to replicate these results. The National CTC trial findings were similar to those of the Pickhardt trial and have reassured many groups that the test can be performed with high accuracy in both academic and private-practice settings [3].

Training and preferably testing of radiologists in CTC is a requirement for optimal reader performance [4]. Participation in a dedicated training program is recommended. These training sessions should provide enough time for the radiologist to become facile with a specific colonography software package and experience interpreting at least 50 proven cases. Polyp-detection testing will allow individuals an opportunity to assess whether additional training is needed before clinical implementation. In order to continue to improve reader performance, it is recommended that patients who undergoing both CTC and subsequent colonoscopy be reviewed retrospectively to assess for CTC false-positive and false-negative detections. This quality improvement review offers a rich experience for learning and gaining expertise, confidence, and competence. Strict adherence to state-of-the art CTC protocol requirements is also recommended, including stool- and fluid-tagging regimens, mechanical insufflation of the colon, thin-section data acquisition, and lowdose CT techniques [5]. It is clear that meticulous attention to all aspects of the examination and interpretation is required to achieve the best results.

Approximately 40 million US adults aged ⩾50 have not undergone a sigmoidoscopy or colonoscopy within the previous 10 years or a fecal occult blood test (FOBT) within the preceding year [6]. The major disincentive for patients undergoing a full structural colorectal examination is the laxative purgation [7]. Work is being done to reduce the burden of laxation either with the use of a partial colon preparation [8] or without cathartic preparation [9]. Although not considered standard of care, evidence from feasibility trials is promising and may translate to better patient acceptance.

The advantages of CTC include the lack of required sedation and intravenous line placement, a quick return to work following the examination, and the convenience of no driving restrictions following the test; the disadvantage is that if a significant polyp is identified, patients must undergo colonoscopy and polypectomy. If same-day colonoscopy is not offered, then the patient must undergo a second bowel preparation, spend another day away from work, and experience added worry and inconvenience. In a screening population, including false-positive interpretations, the prevalence of patients being referred from CTC to colonoscopy for polypectomy is 12% when a 6-mm threshold is applied [2, 3]. This translates into an 88% chance that an individual patient will not require a second procedure, thereby mitigating concerns for redundancy. Those with a high likelihood of polyps may best be triaged to colonoscopy screening.

The main risk for patients at CTC is colorectal perforation. The symptomatic perforation rate is estimated to be 1:20,000 examinations, and likely safer when screening patients [10]. In contrast, colonoscopy perforation rates are in the range of 1:1,000 [11], often but not always related to biopsy procedures. Bleeding can also occur following colonoscopy intervention and is more common than perforation.