Endoscopic and histologic correlates of colorectal polyp bleeding.

Until now, the exact mechanism of bleeding from colorectal polyps has not been demonstrated. The present study aimed to identify macroscopic factors and the main source of polyp bleeding. One hundred fifty-seven cases of single colorectal polyp from a variety of clinical situations were investigated to determine whether surface area, shape, color, and location in the colon were correlated with a positive result in the fecal occult blood test. We also searched for the site of bleeding on the surface of polyps under a dissecting microscope and investigated the relationship between bleeding and microerosion and thin surface epithelium on the maximal vertical cross-section of the polyp. The presence of fecal occult blood was found to be correlated with the surface area of colonic polyps. We demonstrated that a red color tone of polyps was caused largely by microerosion and that the area of both microerosion and thin surface epithelium was significantly larger on polyps associated with a positive fecal occult blood test result. The extent of microerosion and thin surface epithelium was found to be correlated with the polyp surface area and villous component. These observations strongly suggest that the area of microerosion and thin surface epithelium tends to increase as the surface area expands, resulting in a higher rate of detection of polyps with malignant potential by the fecal occult blood test.