Esophageal varices are caused by an increase in pressures in the portal vein, the blood vessel that connects the liver to the digestive organs. This elevated pressure is called portal hypertension. This increase in pressure causes a back up of blood that makes the blood vessels in the esophagus (and/or stomach) enlarge, swell and become very fragile. The increase in pressure is typically caused by liver disease, such as cirrhosis or hepatitis.
The swollen blood vessels are sensitive, and can bleed easily. When the vessels rupture, the bleeding can be life-threatening and requires immediate medical attention.