MINUTE ADENOMAS OF THE DEPRESSED TYPE IN FAMILIAL ADENOMATOUS POLYPOSIS OF THE COLON - A PATHWAY TO ORDINARY POLYPOID ADENOMAS

Background. It has been thought that colorectal adenomas are polypoid from their beginning. Although depressed adenomas have been described, they have been considered an unusual form and have not been studied s ystemically. Method. More than 5000 colorectal adenomas in 24 resected large intestines of patients with familial adenomatous polyposis were examined by dissecting microscopic study. These adenomas were classif ied by their surface appearance as depressed, flat, or polypoid type. The frequencies and sizes of the three types were determined. Results. In addition to ordinary polypoid adenomas, many adenomas of the depre ssed type were found. Of the 5287 adenomas detected, 635 (12.0%) were depressed, 967 (18.3%) were flat, and 3685 (69.7%) were polypoid. Depr essed adenomas constituted approximately 15% of all adenomas smaller t han 1.5 mm diameter. However, they were rare in those of 1.5-2.0 mm di ameter and were not found among those of more than 2.0 mm in diameter. Conclusion. These findings suggest that some ordinary polypoid adenom as originate from minute depressed adenomas.