A small adenomatous polyp (tubular adenoma) is seen here. This lesion is called a "tubular adenoma" because of the rounded nature of the neoplastic glands that form it. It has smooth surfaces and is discrete. Such lesions are common in adults.
Diminutive and small polyps are virtually always benign. Adenomas can be classified as diminutive (1 to 5 mm in diameter), small (6 to 9 mm), and large (≥10 mm). Advanced adenomas are either ≥10 mm or are <1 cm with at least 25% villous features, high-grade dysplasia, or carcinoma. Tubulovillous denomas have 25 to 75% villous features. Villous adenomas have >75% villous architecture. Those larger than 2 cm carry a much greater risk for development of a carcinoma, having randomly collected mutations in genes such as APC, K-RAS, p53, and DNA mismatch repair over the years.
The colonoscopic appearance of rectal polyps that proved to be tubular adenomas are seen below.