Histological assessment of colorectal adenomas by size. Are polyps less than 10 mm in size clinically important?

To define the relative risk of malignant transformation in colorectal adenomas less than 10 mm in diameter.

Prospective study.

District general hospital, UK.

1228 polyps detected endoscopically in 445 patients over the 10-year period 1989-1999.

Site, size, histological type and dysplastic grade of polyp.

657 of the 1228 polyps were adenomas: 281 (43%) tubular, 339 (51%) tubulovillous and 37 (6%) villous. In the 357 adenomas less than 10 mm in diameter, 11 (3%) were severely dysplastic and 2 carcinomas were detected, though neither was less than 5 mm in size. The relative risk of malignancy or severe dysplasia in adenomas of 10 mm or more compared with those of less than 10 mm was 3.8 (p < 0.0001).

Although severe dysplasia and malignancy do occur in adenomas less than 10 mm in size, they are rare in lesions of less than 5 mm. We recommend routine destruction of all polyps 5 mm or more in size, though it is not essential to remove those of less than 5 mm if they are kept under surveillance.