An abnormality in the liver which can impede the return of blood from the intestine to the liver; it can lead to distention and increased pressure in the veins around the esophagus, the stomach, and the intestine. This can rupture, leading to possibly life-threatening gastro-intestinal bleeding. In addition, portal hypertension can cause spleen enlargement and hypersplenism resulting in low red blood cell, white blood cell and platelet counts.