Colonic polyp. Coloured barium X-ray of a pedunculate (stalked) polyp (yellow/pink, upper centre) growing in a colon (large intestine). Part of the colon is seen, running from bottom left to top left then down to lower right. A polyp is a growth which protrudes from the mucous lining of an organ. Although usually harmless, polyps in the colon can eventually become malignant, and so are often removed surgically.