Rectal Bleeding (cont.) What are the causes of rectal bleeding? Many diseases and conditions can cause rectal bleeding. Common causes include anal fissures, hemorrhoids, cancers and polyps of the rectum and colon, diverticulosis, abnormal blood vessels (angiodysplasia), ulcerative colitis, ulcerative proctitis, Crohn’s colitis, infectious colitis, ischemic colitis, and Meckel’s diverticula. an anal fissure is a [...]