An anorectal abscess is a collection of pus in the anal or rectal region. It may be caused by infection of an anal fissure, sexually transmitted infections, or blocked anal glands. Symptoms include painful, hardened tissue in the perianal area, discharge of pus from the rectum, a lump or nodule, tenderness at the edge of the anus, fever, constipation, or pain associated with bowel movements. Treatment involves drainage of the abscess.