A fistula is an abnormal connection between an organ, vessel, or intestine and another organ, vessel or intestine, or the skin. Fistulas can be thought of as tubes connecting internal tubular structures, such as arteries, veins, or intestine, to one another or to the skin. Fistulas are usually the result of trauma or surgery, but can also result from infection or inflammation. Inflammatory bowel disease, such as ulcerative colitis or Crohn's disease, is an example of a disease which leads to fistulas between one loop of intestine and another (enetero-enteral fistula) or intestine and skin (enterocutaneous fistula). Trauma can lead to fistulas between arteries and veins (arteriovenous fistulas).