The significance of ectopic crypt formation in the differential diagnosis of colorectal polyps

Background Ectopic crypts, defined as abnormally positioned crypts that have lost their orientation toward the muscularis mucosae, have been suggested to be the best defining histologic feature of traditional serrated adenoma (TSA). However, the significance of ectopic crypt formation (ECF) in the distinction between TSA and conventional adenoma (CA) has rarely been studied. Methods We designed this study to determine if ECF can be found in CA and its presence is exclusive to TSA. We studied 107 TSAs and 191 CAs including 106 tubular adenomas (TAs), 66 tubulovillous adenomas (TVAs), and 19 villous adenomas (VAs). Results ECF was identified in most (79.4%) but not all TSAs. Additionally, ECF was not infrequent in CA (62 of 191, 32.5%), and its presence correlated with the presence of a villous component and larger tumor size (each p <0.001). Conclusions Based on its strong association with the presence of a villous component and larger tumor size, ECF appears to be involved in the protuberant growth of colorectal CA. Because ECF can be found in CA, particularly in cases with a villous component, the possibility of CA should be considered before making a diagnosis of TSA when encountering colorectal polyps with ECF. Virtual Slides The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_212