What is the most important radiographic predictor of malignancy arising in a polyp?
Size is the most important predictor of malignancy present in a polyp; the larger the polyp, the greater the chance of malignancy. The amount of villous change is a much less important factor. About 1% of tubular adenomas smaller than 1 cm are malignant; 10% of tubular adenomas 1 to 2 cm are malignant, and 35% of tubular adenomas larger than 2 cm are malignant. About 10% of villous adenomas less than 2 cm are malignant, and about 50% of villous adenomas larger than 2 cm are malignant. The presence of a pedicle longer than 1 cm means that a pedunculated polyp has a greater than 95% chance of benign behavior, regardless of the histology in the head of the polyp.