Well-differentiated adenoma at the anorectal junction.

Twenty-six cases of patients having adenomatous polyps at the anorectal junction are presented. Most polyps in this region were well-differentiated, and atypical polyps were infrequently seen. Well-differentiated adenomatous polyps in the anorectal junction were larger in average size than ordinary colorectal polyps having the same grade of epithelial pseudostratification. The reason adenomatous polyps at the anorectal junction grow to large sizes with only a relatively rare occurrence of malignant degeneration is discussed in relation to their specific location. Some well-differentiated adenomas were considered to develop secondarily in the bases of hemorrhoids or in pre-existing fibrous polyp that were the end result of hemorrhoids.