Portal hypertension is an increase in the blood pressure within a system of veins called the portal venous system. Normally, the veins come from the stomach, intestine, spleen, and pancreas - then merge into the portal vein, which then branches into smaller vessels and travels through the liver. The most common causes are cirrhosis, hepatitis, alcohol abuse, and blood clots in the portal veins.
If the vessels in the liver are blocked, it is hard for the blood to flow causing high pressure in the portal system. When the pressure becomes too high, the blood backs up and finds other ways to flow back to the heart. The blood can travel to the veins in the esophagus (esophageal varices), in the skin of the abdomen, and the veins of the rectum and anus (hemorrhoids) to get around the blockages in the liver.