Yener, Nese ArzuMidi, AhmetCelikel, Cigdem Ataizi2024-07-122024-07-1220141300-494810.5152/tjg.2014.26982-s2.0-84902593325https://dx.doi.org/10.5152/tjg.2014.2698https://hdl.handle.net/20.500.12415/8570Background/Aims: Colorectal flat adenomas (FAs) may represent a different histogenesis, since their malignant potential is thought to be higher than polypoid adenomas of the same size. In this study, we classified FAs of <= 5 mm into three subgroups-superficially elevated adenomas (SEAs), completely flat adenomas (CFAs), and depressed adenomas (DAs)-based on their low microscopic shapes and compared their clinicopathological features with polypoid tubular adenomas (pTAs) with the same size. Materials and Methods: One hundred one pTAs and 46 FAs with tubular morphology with the same size (<= 5 mm) were studied. Results: The percentages of high-grade dysplasia in FAs and pTAs were 19.56% and 12.87%, respectively. The percentages of the high-grade dysplasia were 28.57%, 13.63%, and 20.00% in the DA, SEA, and CFA subgroups, respectively. FAs had a significantly higher number of normal epithelium at the basal crypts of the lesion than the pTAs (p=0.001). The presence of pericryptal mesenchymal cells was higher in pTAs than the FAs (78.21% vs 10.86%) (p<0.001). Conclusion: Flat adenoma represents a distinct type of colorectal adenoma with special histopathological properties-existence of a normal epithelium at the basal crypts, lack of pericryptal mesenchymal cells, and a high percentage of high-grade dysplasia-especially when it has a depressed shape at low magnification.eninfo:eu-repo/semantics/openAccessFlat colorectal adenomanon-polypoid colorectal neoplasiacolorectal carcinogenesiscolorectal adenomacolorectal adenomatous polypArticle28124918126Q32422122925WOS:000338051700004Q4