sentences:  Traumatic intestinal fistulas usually occur between two loops of intestine (entero-enteric fistula) or intestine and skin (enterocutaneous fistula).Portacaval anastomosis, by contrast, is a veno-venous anastomosis between a vein of the portal circulation and a vein of the systemic circulation, which allows blood to bypass the liver in patients with portal hypertension, often resulting in hemorrhoids, esophageal varices, or caput medusae.Circulatory anastomoses between monochorionic twins may result in twin-to-twin transfusion syndrome.