Clinical significance of small colorectal polyps

Since the concept of "advanced" or "dangerous" adenomas was introduced in 1992, less concern has been directed to diminutive colorectal adenomas. They apparently confer no increased risk of metachronous colorectal cancer and some investigators have suggested that they need neither follow-up nor treatment. This study is intended to discover how often small colorectal adenomas have unfavorable histologic features.

Since 1995 the details of all colorectal polyps have been entered into a database, along with data concerning patients, symptoms, treatment, and outcome. Using this database all adenomas were categorized into three groups: Group I, <6 mm diameter, Group II, 6 to 10 mm diameter, and Group III, >10 mm diameter. "High risk" adenomas were defined as those containing >25 percent villous architecture, those with severe dysplasia, and those over 10 mm in size. Thus all Group III adenomas are high-risk by definition. The effects of family history, patient age, and polyp location on the proportions of Group I and Group II adenomas that were histologically high risk were examined.

There were 5,722 polyps of which 4,381 (76.6 percent) were Group I, 666 (11.6 percent) were Group II, and 675 (11.8 percent) were Group III. These included 24 invasive cancers (2 in Group I, 1 in Group II, and 21 in Group III. Of the Group I adenomas, 91/2,064 (4.4 percent) were high risk compared to 65/417 (15.6 percent) in Group II. Of the 564 Group III adenomas, 326 (57.8 percent) had unfavorable histology. There was no effect of age, family history, or site of the polyp on the proportion of polyps that were high risk.

Four percent of adenomas less than 6 mm diameter and 16 percent of those between 6 and 10 mm have unfavorable histology. Small adenomas can still be clinically significant and should not be ignored. Since the concept of "advanced" or "dangerous" adenomas was introduced in 1992, less concern has been directed to diminutive colorectal adenomas. They apparently confer no increased risk of metachronous colorectal cancer and some investigators have suggested that they need neither follow-up nor treatment. This study is intended to discover how often small colorectal adenomas have unfavorable histologic features.