A hernia in the upper stomach, or hiatal hernia, is caused when weakened muscles allow part of the stomach to push up through the diaphragm, according to Mayo Clinic. Doctors are not sure why this happens.
A hiatal hernia is caused by injury or heavy and persistent pressure on the muscles around the hiatus, which is the opening in the diaphragm that allows the esophagus to pass into the stomach, says Mayo Clinic. This pressure is caused by the frequent lifting of heavy objects, strenuous vomiting, coughing or straining at stool. Pregnancy and childbirth is also a cause of hiatal hernia, according to Cleveland Clinic. Some people are born with an uncommonly large opening in the diaphragm that allows the stomach to bulge through. Other things that put people at risk for a hiatal hernia are obesity and being 50 years old or older.
There are two types of hiatal hernia, says Cleveland Clinic. In a sliding hiatal hernia, the area where the esophagus and the stomach join both slide up into the patient's chest cavity. In a paraesophageal hernia, part of the actual stomach pushes up through the hiatus and is squeezed in next to the esophagus. This puts the stomach at risk for having its blood flow cut off.