Abdominal hernias, also called external hernias, are when an abdominal organ, or part of an abdominal organ protrudes through the abdominal wall, usually at a site of weakness. They can be classified into midline hernias and groin hernias. Most frequent types of midline hernias are the epigastric and umbilical hernias, while groin hernias can further be classified into inguinal and femoral hernias. There’s also incisional hernias, which is when contents herniate through an incisional scar from a previous abdominal surgery
Now, the abdominal wall is made up of a few layers. The deepest layer is the visceral peritoneum, which covers many of the abdominal organs and lines the peritoneal space. That layer wraps around to form the parietal peritoneum. Then, moving externally, there is the extraperitoneal fat, the transversalis fascia, the muscle layer with the internal and external oblique and transversus abdominis aponeurosis and a layer of fascia which has different names in different regions. Ok, so anything that increases the pressure of the abdominal cavity may result in a sac that forms in the abdominal wall through which organs might protrude.
When organs protrude through the midline, that results in a midline hernia. Midline hernias include the epigastric hernia, which is when abdominal organs herniate through the linea alba, or the part of the midline between the xiphoid process and the umbilicus. With umbilical hernias, on the other hand, the organ protrudes through the umbilicus.
And then there’s groin hernias, which can be classified into inguinal hernias, the more common type, and femoral hernias.