MSH: Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body.,MEDLINEPLUS: <p>A fistula is an abnormal connection between two parts inside of the body. Fistulas can happen because of injury, infection or inflammation. They may develop between different organs such as between the esophagus and the windpipe, or the bowel and the vagina. They can also develop between two blood vessels such as between an artery and a vein, or between two arteries. </p>,NCI: An abnormal opening or passage between two organs or between an organ and the surface of the body. Fistulas may be caused by injury, infection, or inflammation, or may be created during surgery.