Flat polyps of the colon: accuracy of detection by CT colonography and histologic significance

There is controversy regarding the prevalence, clinical importance, and appropriate screening methods for nonpolypoid (flat and depressed) polyps in the colon. Investigators in Japan have reported higher prevalence of nonpolypoid adenomas in the general population and there have been several reports of higher incidence of high-grade dysplasia in flat adenomas in these Eastern studies. Historically, many Western gastroenterologists have been skeptical of these findings and there have been conflicting studies regarding the prevalence of flat adenomas and incidence of high-grade dysplasia in these lesions. Multiple reasons have been postulated for this apparent difference. Therefore further research into this topic is needed to clarify these issues. In this article we will review the controversy related to the definitions and clinical importance of nonpolypoid neoplasms in the colon, demonstrate the appearance of these unique lesions at CT colonography (CTC) and discuss the accuracy of CTC.