Flat, depressed and polypoid colorectal lesions: a comparative study using a index of histological advance]

It has been described that the histological changes in flat and depressed colon lesions are more advanced than the ones in polypoid lesions.To compare the histological findings in flat or depressed (non polypoid) and elevated (polypoid) colon lesions. To validate the use of a newly developed Histological Advance Index to compare results.Prospective observational study. Population in study consisted of adult patients programmed for an elective colonoscopy at a private endoscopy center in Lima- Perú. Two groups: 417 found to have non polypoid lesions (which included flat, depressed and lateral spreading tumors or LST), and 405 with polypoid lesions.Total of 8,248 patients, with 417(5%) in the non polypoid group; 368(4.5%) in the flat lesion group, 27(0.32%) in the depressed and 22 (0.26%) LSTs. According to our index, flat and polypoid lesions showed no difference in histological findings. LSTs had a more advanced histology and depressed lesions reached the highest index scores. Flat lesions were found more often in right colon compared with polypoid ones (31% vs 22%, p<0.01), with a higher percentage of serrated lesions (9% vs 2%, p<0.01) and high grade dysplasia (5% vs 3%, NS). In contrast, depressed lesions, showed high grade dysplasia in 3.7% (NS) but cancer in 18% (p<0.01) LSTs were found mainly in right colon and rectum, showing villous component in 23%(p< 0.01) and high grade dysplasia in 32%(p <0.01), but no cancer was found.Flat and polypoid lesions showed similar histological findings, but LSTs were found to have a higher prevalence of villous lesions and high grade dysplasia. Depressed lesions were found to have a higher prevalence of malignancy. Histological Advance Index proved to be a useful tool to compare groups and quantify differences. .