Rectal disorders. Artwork of a section through the rectum. Rectal polyps (centre left, red and lower centre, pink) are small benign growths on the rectal lining. They could potentially become a rectal carcinoma (pink) and therefore should be removed. Internal and external haemorrhoids (blue) are blood vessels that have become dilated and swollen due to high internal pressure. An anal fistula (below internal haemorrhoid) is a split in the rectum that forms into a channel that opens in the skin. It is caused by infection and inflammation. An abscess (lower right), is a pocket of pus formed due to a bacterial infection.