The esophagus has small veins just beneath its surface lining. The nutrients absorbed from the intestine reach the liver and are processed. Blood flows through the liver into the inferior vena cava, then up into the heart. When cirrhosis (scarring) of the liver develops, the normal flow of blood from the portal vein through the liver is blocked (partially or even completely). Blood must then return to the heart by other routes. One such route is through the esophageal veins.
The esophageal veins are normally quite small but with the increased flow of blood become quite dilated and are then known as varices. Varices sometimes rupture if the blood flow becomes too great resulting in gastrointestinal hemorrhage. This is a serious situation and requires immediate medical attention. A physician can pass a scope called an endoscope through the mouth down into the esophagus and inject the varices with a chemical which will stop the bleeding. This technique is called endoscopic variceal sclerosis or sclerotherapy. Usually these injections need to be repeated to decrease the size of the varices and prevent further bleeding.