Incidental Findings Found In Typical Screening Populations Undergoing Colorectal Cancer Screening with Computed Tomography Colonography: A Systematic Review
Background: CT colonography (CTC) is a noninvasive technology used to screen for colorectal cancer. Unlike other screening modalities, CTC provides a view of the abdomen and pelvis allowing radiologists to detect lesions in extracolonic organs. There is much debate on the balance of potential benefits versus potential harms of discovering, working up and treating these extracolonic findings. This debate might be especially relevant for asymptomatic populations receiving screening with CTC. Purpose: This systematic review aims to determine the frequency and clinical implications of finding incidental, extracolonic lesions during CT colonography (CT) in asymptomatic, screening populations. In addition, this review reports the frequency and clinical outcomes of clinically important lesions. Lastly, this review summarizes the various methods studies used to define the clinical significance of incidental findings. Data Sources: I carried out a systematic search of MEDLINE, Embase, the Cochrane Clinical Trials databases and published reviews up to March 2012. Study Selection: Two investigators independently reviewed 282 abstracts and 53 full text articles using a set of predefined inclusion and exclusion criteria. Both reviewers carried out independent critical appraisals of each study using criteria developed by the United States Preventive Services Task Force. Data Extraction: One reviewer extracted information on study samples, designs, populations, interventions and outcomes from six studies. A second reviewer verified this information for accuracy. Data Synthesis: The frequency of extracolonic findings (ECFs) ranged from 27.2% to 68.9% (mean 49.3%). Included studies used similar classification systems of clinical importance, which were primarily based on the likelihood of clinical workup. Studies reported that 5.6% of the reported ECFs were of high clinical importance and 15.5% of lesions were either moderate- or high-importance. A minority of these findings represented lesions that could have benefitted from early diagnosis and intervention. Studies reported that 0.09% to 1.2% of subjects were diagnosed with AAAs and 0.23% to 0.88% were diagnosed with extracolonic cancers. Studies used widely varying lengths and methods of following ECFs, making it difficult to estimate the true clinical implications of incidental findings. However, the range of moderate/high to high-importance findings (5.6% to 15.5%) provides a good estimate of the number of subjects requiring some clinical workup. Limitations: I identified several weaknesses of the available literature on ECFs from screening CTC. For instance, many included studies suffered from poor follow-up and incomplete reporting of outcomes. In addition, no studies properly addressed the potential physical and psychological harms of being diagnosed, worked up and treated for extracolonic findings. Lastly, the included literature does not address how ECFs are handled in non-academic settings. This systematic review also had several weaknesses. The decision to limit the review to screening populations might reduce the strength of my findings. I attempted to compensate by including populations at high risk of CRC and studies conducted outside the US, but this might have reduced the generalizability of my findings. Furthermore, I were unable to adjust for different follow-up time periods, making it difficult to compare the clinical outcomes of ECFs among included studies. Lastly, I attempted to develop an outcomes table for ECFs from screening CTC, but were unable to do so because of the imprecision of results, variable periods of follow-up and gaps in reported outcomes. Conclusions: Based on these results, a large proportion of individuals receiving CT colonography for colorectal cancer screening will have an extracolonic lesion discovered. Roughly one-fifth to one-third of these findings will receive some clinical workup and the majority of these will ultimately be diagnosed as benign. Since a small percentage of potentially important findings will result in clinical benefit, it is possible that the classification systems are overly sensitive. In addition, the reporting of all extracolonic findings might result in unnecessary testing and patient anxiety. Unfortunately, the existing data does not provide enough certainty to know which lesions can go unreported without putting the patient at harm. However, based on the evidence, it appears that most radiologists and primary care physicians err on the side of reporting findings, which also results in unnecessary harms to patients. Another source of unnecessary and potentially harmful care is the large variability in radiologist interpretation of extracolonic findings. Based on this review, there are no indications that the development of a standardized classification system of ECFs has successfully reduced this variation. There are two primary ways to improve this practice variability in the future. First, classification systems could be improved to provide more guidance, especially for findings that have an uncertain balance of benefits and harms. More primary research might be required before this is possible. Second, training programs for CTC should require specific training for interpreting ECFs, including the proper follow-up of specific findings.Master of Public Healt
