Content Reviewers:Viviana Popa, MD
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.
With inguinal hernias, the contents of the abdominal cavity, usually fat or part of the small intestine, protrude through the inguinal canal.
The inguinal canal lies between the muscles of the anterior abdominal wall.
The canal is bound superiorly by the internal oblique and transversus abdominis muscles, anteriorly by the external and internal oblique aponeurosis, inferiorly by the inguinal ligament, and posteriorly by the transversalis fascia and conjoint tendon.
Finally, the inguinal canal also has two openings: an internal one, called the deep inguinal ring, which is an orifice of the transversalis muscle fascia, located lateral to the inferior epigastric vessels, and an external one, called the superficial inguinal ring, which is an opening in the external oblique muscle aponeurosis.
Now, remember that the inguinal canal forms during embryological development.
The process begins when a projection of peritoneum called the processus vaginalis herniates through the abdominal body wall, to allow the gonads, testes in males, and ovaries in females, to descend from the abdomen, where they formed, to their final location in the scrotum, or pelvis, respectively.
When the gonads have descended completely, the processus vaginalis is obliterated, closing off the tunnel.
But even though both males and females have inguinal canals, since the testes have a longer journey ahead, this makes the inguinal canals larger and more prominent in males, creating a physiological site of weakness in the abdominal wall.
This makes inguinal hernias far more common in genetically male individuals, so we’re going to be referring to this population moving forward.
Now, inguinal hernias can be classified as indirect, or direct.
Indirect inguinal hernias occur when the processus vaginalis fails to close during after the testes have passed through it, so this is considered a congenital hernia.
Due to the congenital aspect associated with it, indirect inguinal hernia typically occurs in infants and children, but it can also be discovered in adulthood.
When the processus vaginalis remains open, intra-abdominal organs, like the intestines, can herniate through the inguinal canal.
Specifically, with indirect inguinal hernias, the organs herniate lateral to the inferior epigastric vessels, through the internal and external rings of the inguinal canal, and end up in the scrotum.
On the other hand, direct inguinal hernias are acquired hernias that result from the weakening of the transversalis fascia.