Flat elevated lesions of the colon and rectum: a spectrum of neoplastic and nonneoplastic entities

The aim of this prospective study is to establish the frequency and the type (neoplastic and nonneoplastic) lesions defined endoscopically as flat elevated lesion (FEL) in the colon and rectum, as well as to compare flat adenomas (FAs) to polypoid lesions of the same size with morphometric and immunohistochemical analysis. One hundred nineteen patients were studied through fibrocolonoscopy with chromoscopy (indigo carmine spray). All detected lesions (total of 195) were removed, and FELs measuring 10 mm or smaller were also selected. Using histopathologic criteria, they were divided in neoplastic (adenomas and carcinomas) and nonneoplastic ones. In neoplastic lesions, the following parameters were evaluated to compare FAs with polypoid lesions: morphometric studies with Index of Structural Atypia (ISA) and Stratification Index (SI), evaluation of cellular proliferation with label index of Ki-67, and expression of p53 protein. Of 195 lesions resected, only 33 (17%) met the endoscopic requirements for FELs. Twelve (36.4%) were neoplastic and 21 (63.6%) considered nonneoplastic. Among the FAs, there were a percentage of high-grade (severe dysplasia) significantly more frequent than observed in polypoid lesions (16.7% vs 2.6%). In addition, the SI, Ki-67 label index and p53 positivity were significantly higher in FAs. The ISA also reached significant differences between both groups of adenomas. Non-neoplastic FELs included different entities such as hyperplasic polyps, focuses of colitis, normal mucosa, and scars. The endoscopic elements analyzed were shared between nonneoplastic FELs and FAs. A central depression, when air was properly insufflated, considered typical in neoplastic lesions, was frequently observed in nonneoplastic lesions. Following the endoscopic criteria of FELs, nonneoplastic lesions predominated over the adenomatous lesions, demonstrating that FELs and FAs are not homologous terms. The frequency of high-grade dysplasia was significantly more elevated in the adenomatous FELs than in polypoid adenomas. The ISA, SI, p53 expression, and Ki-67 label index were helpful in differentiating adenomatous FELs from polypoid lesions. Flat elevated lesions selected by endoscopic criteria are, in fact, a heterogeneous population of lesions.