MODEL RELEASED. Hernia operation. Surgeons performing surgery to repair an epigastric hernia in a patient's abdomen. A hernia is the abnormal protrusion of an organ or tissue through an opening. The most common site of hernias is the abdomen, when a weakness in the abdominal wall evolves into a localized hole, or 'defect', through which adipose (fat) tissue, or abdominal organs covered with peritoneum (the lining of the abdominal cavity), may protrude. An epigastric hernia occurs in the epigastrum, the upper central region of the abdomen.